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Issued under the authority of the Home Office(Fire and Emergency Planning Directorate)

Fire Service Manual

Volume 2Operational

Firefighting Foam

The Fire ServiceCollege

* 0 0 0 8 6 3 8 3 S *

HM Fire Service Inspectorate Publications Section

London: The Stationery Office

•

Firefighting Foam

© Crown Copyright 1998Published with the permission of the Home Officeon behalf of the Controller of Her Majesty's Stationery Office

Applications for reproduction should be made inwriting to The Copyright Unit, Her Majesty's Stationery Office,S1. Clements House, 2-16 Colegate, Norwich. NR3 ISQ

ISBN 0 11 341186 3

Cover photograph:

Northern Ireland Fire Brigade

Half-title page photograph:

Northern Ireland Fire Brigade

Printed in the United Kingdom for The Stationery OfficeJ67054 12/98 C50 5673

Preface

This manual, Volume 2, Fire Service Operations ­Firefighting Foam. deals with the production offoam, categories of fires and foams, applicationrates and the operational use of foam. Specificpractical scenarios are also discussed.

A second manual is also [Q be provided underVolume 1, Fire Service Technology, Equipmentand Media. This will deal with the technicalaspects of foam concentrates, standards andequipment.

These books will replace:

The Manual of Firemanship Book 3. Part 3

Dear Chief Officer Letter 2/97 - FoamApplication Rates.

The Home Office is indebted to all those who havehelped in the preparation of this work, in particular:

Mr Bryan Johnson BSc.;Home Office Fire Experimental Unit;S.D.O. M. George, Mid and West Wales

Fire Brigade:Angus Fire Armour Ltd;Williams Fire and Hazard Control Inc.:Civil Aviation Authority;British Fire Protection Association Ltd;Cheshire Fire Brigade:London Fire Brigade:Fire Service College: andOr Tony Cash.

Home Office, September 1998

Firejighling FoamIII ~

_______________________11

Firefighting Foam

Contents

Preface

Chapter 1 Introduction

Chapter 2 Production of Finished Foam

2.1 General2.2 Percentage Concentration2.3 Aspiration2.4 Foam Expansion Ratios

Chapter 3 Categories of Fir and Firefighting Foams

3.1 Classes of Fire3.2 Electrical Fires3.3 Types of Liquid Fuel Fire

Chapter 4 Re 'ommended linimum Application Rates

4.1 General4.2 Fires Involving Water-immiscible Class B Liquids4.3 Fires Involving Water-miscible Class B Liquids

Chapter 5 Operational Use of Foam on Cia B Liquid Fuels

5.1 General5.2 Low Expansion Foam5.3 Medium Expansion Foam5.4 High Expansion Foam

Chapter 6 Practi al cenario

6.1 General6.2 Preplanning6.3 Scenarios

Chapter 7 Storag Tank Fires

iii

1

33445

99

1313

17171717

2121222829

35353535

497.17.27.37.47.5

IntroductionCommon Problems With Refineries and Storage Tank FarmsTank SizeFire DevelopmentPractical Scenarios

4949505052

Firejighling Foam V [

__________________--------..;.J

Chapter 8 Logi tic of Dealing With Larg

8.1 Introduction8.2 Conventional Fire Attack8.3 Technical Options

References

Further Reading

Glossary of Terms - Firefighting Foams

VI Fire Service Mallual

Storage Tanke

1 ire 65

656574

87

87

89

Firefightin Foam

Firefighting Foam Ch pte

Chapter 1 - Introduction

The main properties of firefighting foams include:

Some firefighting foams have also been developedspecifically for use against class A fires.

• Knockdown and extinction: the ability ofthe finished foam to control and extinguishfires.

• Expansion: the amount of finished foamproduced from a foam solution when it ispassed through foam-making equipment.

Burn-back resistance: the ability of the fin­ished foam, once formed on the fuel, tostay intact when subjected to heat and/orflame.

• Stability: the ability of the finished foam toretain its liquid content and to maintain thenumber, size and shape of its bubbles. Inother words, its ability to remain intact.

leads to the complete destruction of the foamblanket. Consequently, special firefighting foams,generally known as 'alcohol resistant' foam con­centrates, have been developed to deal with theseparticular types of liquid.

• Fluidity: the ability of the finished foam tobe projected on to, and to flow across, theliquid to be extinguished and/or protected.

• Sealing and resealing: the ability of thefoam blanket to reseal should breaks occurand its ability to seal against hot and irregu­lar shaped objects.

• Contamination resistance: the ability of thefinished foam to resist contamination by theliquid to which it is app[ied.

•

Firefighting foams have been developed primarilyto deal with the hazards posed by liquid fuelfires.

Water is used for most firefighting incidents,however it is generally ineffective against firesinvolving flammable liquids. This is becausewater has a density that is greater than most flam­mable liquids so, when applied, it quickly sinksbelow their surfaces, often without having anysignificant effect on the fire. However, whensome burning liquids, such as heavy fuel oils andcrude oi Is, become extremely hot, any water thatis applied will begin to boil. The resulting rapidexpansion as the water converts to steam maycause burning fuel to overflow its containmentand the fire to spread - this event is known as aslop-over. Also, the water that sinks below thefuel will collect in the container and, should thecontainer become full, this will result in the fueloverflowing.

Finished firefighting foams, on the other hand.consist of bubbles that are produced from a com­bination of a solution of firefighting foam concen­trate and water that has then been mixed with air.These air filled bubbles form a blanket that floatson the surface of flammable liquids. In so doing,the foam suffocates the fire and can lead to theknockdown and extinction of the flames.

The low density of firefighting foam blankets alsomakes them useful for suppressing the release ofvapour from flammable and other liquids. Specialfoam concentrates are available which allowvapour suppression of many toxic chemicals.

Water-miscible liquids, such as some polar sol­vents, can pose additional problems for firefight­ers. These quickly attack finished foams byextracting the water they contain. This rapidly

Firefighting Foam 1

Firefighting Foam Chapter

The performance of firefighting foams can begreatly influenced by:

• The type of foam-making equipment usedand the way it is operated and maintained.

• The type of foam concentrate used.

It must be stressed that this Manual only givesgeneral information on the use of firefightingfoams. Incidents requiring the use of foam arevaried and preplanning in support of an effec­tive risk assessment at the commencement of anincident is of the utmost importance to ensurethat the correct foams, equipment and tacticsare selected and employed.

Chapter 2 - Production of Finished Foam

• The type of fire and the fuel involved.

2.1 General

Finished foam is produced from three main ingre­dients; foam concentrate, water and air. There areusually two stages in its production. The firststage is to mix foam concentrate with water toproduce a foam solution. The foam concentratemust be mixed into the water in the correct pro­portions (usually expressed as a percentage) inorder to ensure optimum foam production andfirefighting performance. This proportioning isnormally carried out by the use of inductors (orproportioners) or other similar equipment. Thisresults in the production of a 'premix' foam solu­tion. In other words, the foam concentrate andwater have been mixed together prior to arrivingat the foam-making equipment. Occasionally, pre­mix solutions are produced by mixing the correctproportions of water and foam concentrate in acontainer. such as an appliance tank, prior topumping to the foam-making equipment. In addi­tion, some types of foam-making equipment are

FinishedFoam

fitted with a means of picking up foam concen­trate at the equipment; these are known as 'self­inducing' with [he mixing taking place in thefoam-making equipment itself.

The second stage is the addition of air to the foamsolution to make bubbles (aspiration) to producethe finished foam. The amount of air addeddepends on the type of equipment used. Hand-heldfoam-making branches generally only mix rela­tively small amounts of air into the foam solution.Consequently, these produce finished foam withlow expansion (LX) ratios, that is to say, the ratioof the volume of the finished foam produced by thenozzle. to the volume of the foam solution used toproduce it, is 20: I or less. Other equipment isavailable which can produce medium expansionfoam (MX) with expansion ratios of more than20: 1 but less than 200: I, and high expansion foam(HX) with expansion ratios of more than 200: I andpossibly in excess of 1000: 1.

1Venturi

ProportionerWater

Figure 2./ The

production offinished

foam

• The tactics of foam application.

This Volume of the Manual describes all aspects ofthe operational use of firefighting foam and in par­ticular its use against class B liquid fuel fires.Topics covered include recommended minimumapplication rates and application techniques; prac­tical scenario considerations; and the logisticsinvolved in dealing with fires in storage tanks.

The most effective and efficient use of firefightingfoam can only be achieved after full considerationhas been given to all of the above factors.

• The length of pre-burn.

• The quality of the water used.

• The rate at which the foam is applied.

The section on firefighting foams in Volume I ofthe Manual describes the technical aspects of fire­fighting foam and discusses the types of equip­ment typically used by the fire service to produceit. Topics covered include the properties of foamconcentrates, finished foams and foam equipment:application rates; and the classes of, and types of,fire for which foam can be used. However, themore important operational aspects included inVolume I are also summarised in Chapters 2,3 and4 of this Volume. At the rear of this Volume, thereis a glossary of terms used in this Manual andother terms that may be used in connection withfirefighting foams.

2 Fire Sel'l'ice Manual Firefighting Foam 3

•

• As it leaves the branch.

• 'Non-aspirated' implies that no aspirationof the foam solution has taken place.

• When it strikes an object. This causes fur­ther turbulence and air mixing. • Low expansion less than or equal

to 20: I

• Medium expansion greater than 20: Ibut less than orequal to 200: I

• High expansion greater than 200: I

such as wetting agents, may be formulated so thatthey do not foam; use of these types of additivewould result in non-aspirated application, eventhrough purpose designed foam-making equipment.

2.4 Foanl Expansion Ratios

(a) General

As mentioned previously, finished foam is usuallyclassified as being either low, medium or highexpansion. The expansion, or more strictly theexpansion ratio. of a foam is the ratio of the vol­ume of the finished foam to the volume of thefoam solution used to produce it.

(b) Equipment Used For GeneratingDifferent Expansion Ratio Foams

Typical firefighting foam expansion ratio rangesare:

Secondary aspirated foams generally have anexpansion ratio of less than 4: I.

Primary aspirated low expansion foams are usual­ly produced by using purpose designed foam-mak­ing branches or mechanical generators.

Secondary aspirated low expansion foams are usu­ally produced by using standard water deliverydevices. Some purpose designed large capacitymonitors have also been produced for this particu­lar type of application (see Chapter 8, Section 3).

Medium and high expansion foams are usually pri­mary aspirated through special foam-makingequipment. This equipment produces foam byspraying the foam solution on to a mesh screen ornet. Air is then blown through the net or mesheither by entrainment caused by the spray nozzle,or by an hydraulic, electric or petrol motor drivenfan.

As it travels through the air due to the tur­bulence produced by the stream.

•

• Primary aspirated foam - finished foamthat is produced by purpose designed foam­making equipment.

Secondary aspiration will normally result in a poorquality foam being produced, due to insufficientagitation of the foam/air mixture. That is to say, thefoam will generally have a very low expansionratio and a very short drainage time. However,foam blankets with short drainage times can beadvantageous if rapid film-formation on a fuel isrequired (see this Chapter, Section 4c).

To more accurately describe the different types offinished foam produced, the terms 'primary' or'secondary' aspirated are preferred:

• Secondary aspirated foam - finished foamthat is produced by all other means, usuallystandard water devices.

There is sufficient air entrained by these processesto produce a foam of very low expansion (oftenwith an expansion ratio of less than 4: I).

Consequently, the term 'non-aspirated foam' isoften used incorrectly to describe the product of afoam solution that has been passed through equip­ment that has not been specifically designed toproduce foam, such as a water branch. However,the use of this type of equipment will often resultin some aspiration of a foam solution. This isbecause air is usually entrained into the jet or sprayof foam solution:

It is highly unlikely that a foam solution can beapplied operationally to a fire in such a way that noaspiration occurs. However, should such circum­stances occur, then this would be referred to as anon-aspirated application. Some water additives,

Water

Foam Concentrate

Figure 2.2 6% Foam Concentrate 94% Water

2.3 Aspiration

It is also very important to have compatibility offoam-making equipment and induction equipment,and just as importantly, foam induction equipmentmust be checked regularly to ensure that it is oper­ating correctly and giving an accurate rate ofinduction.

a foam solution rich in foam concentrate. Not onlywill this result in the foam supply being depletedvery quickly and an expensive waste of foam con­centrate, but it will also lead to finished foam withless than optimum firefighting performance, main­ly due to the foam being too stiff to flow ade­quately. Alternatively, using 3% foam concentratewhere the system is set for I % will result in a solu­tion with too little concentrate to make foam withadequate firefighting performance.

Once the correctly mixed foam solution has beendelivered to the end of a hose line, there are a num­ber of forms in which it can be applied to the fire.Generally, foam application is referred to as beingeither 'aspirated' or 'non-aspirated':

• Aspirated foam is made when the foamsolution is passed through purpose designedfoam-making equipment, such as a foam­making branch. These mix in air (aspirate)and then agitate the mixture sufficiently toproduce uniformly sized bubbles (finishedfoam).

• 3% concentrates3 parts foam concentrate in 97 parts water,

All foams are usually supplied as liquid concen­trates. These must be mixed with water, to form afoam solution, before they can be applied to fires.They are generally supplied by manufacturers aseither 6%, 3% or I% foam concentrates. Thesehave been designed to be mixed with water asfollows:

• 6% concentrates6 parts foam concentrate in 94 parts water,

I % concentrate is basically six times as strong as6% concentrate. and 3% concentrate is twice asstrong as 6% concentrate. However. the firefight­ing characteristics of finished foam produced from1%, 3% and 6% concentrates of a particular typeof manufacturer's foam should be virtually identi­cal.

The following Sections describe in more detailsome of the important factors of foam productionthat were introduced above.

2.2 Percentage Concentration

• 1% concentratesI part foam concentrate in 99 parts water.

The lower the percentage concentration, the lessfoam concentrate that is required to make finishedfoam. The use of say 3% foam concentrate insteadof 6% foam concentrate can result in a halving ofthe amount of storage space required for the foamconcentrate, with similar reductions in weight andtransportation costs, while maintaining the samefirefighting capability. Not all foam concentratesare available in the highly concentrated I% form,e.g. alcohol resistant and protein based foam con­centrates. This is because there are technical limitsto the maximum usage concentrations of some ofthe constituents of foam concentrates.

It is extremely important that the foam inductionequipment used is set to the correct percentage. If3% concentrate is induced by an induction systemset for 6% concentrate, then twice the correctamount of foam concentrate will be used creating

4 Fire Service Manila! FireJighting Foam 5

(c) Foam Concentrates •

Figure 2.3Diagrammaticillustration ofexpansion of differentfoam types.

Primary Aspirated Finished Foams

warehouses, aircraft hangars, cellars,ships holds, mine shafts, etc.Large cable ductsVapour suppression (including cryogenicliquids such as LNG/LPG)

• Secondary Aspirated Finished Foams

Large flammable liquid fires (i.e. storage tanks,tank bunds)HelidecksAircraft crash rescuePortable fire extinguishers

Low expansion finished foams can be projectedover reasonably long distances and heightsmaking them suitable in many situations for useagainst fires in large storage tanks.

Medium expansion finished foam can only beprojected over small distances. However, withexpansions of between 20 and 200, large quantitiesof foam are produced from relatively small quanti­ties of foam solution. This, combined with its abil­ity to flow relatively easily, makes medium expan­sion foam ideal for covering large areas quickly.

such as aircraft crash rescue. However, the foamblanket tends to collapse quickly, so providingvery poor security and resistance to burnback.

Secondary aspirated foam can be thrown over agreater distance than is possible with primary aspi­rated low expansion foam. This has resulted inequipment being designed specifically to projectsecondary aspirated foam into large storage tankfires (see Chapter 5, Section 2b) (iv) and Chapter8, Section 3). Manufacturers of this equipment rec­ommend the use of film-forming foam concentratetypes for such applications. They claim that thefinished foam produced usually has an expansionratio of less than 4: I.

The amount that a foam solution can be aspiratednot only depends on the equipment, but also on thefoam concentrate that is used. For instance, syn­thetic detergent (SYNDET) foam concentrates arethe only type that can be used to produce low,medium and high expansion foams; protein foamconcentrates can only be used to produce lowexpansion foam and the remaining commonly usedfoam concentrates (i.e. AFFF, AFFF-AR, FP, FFFPand FFFP-AR), are mostly intended for use at lowexpansion, although they can also be used to pro­duce medium expansion foam.

For flammable liquid fuel fires, effective sec­ondary aspirated foam can only be produced usinga film-forming foam concentrate.

(d) Typical Uses and Properties of Low,Medium and High ExpansionFinished Foams

The various expansion ratios are typically used forthe following applications:

Low expansionLarge flammable liquid fires (i.e. storagetanks, tank bunds)Road traffic accidentsFlammable liquid spill firesVapour suppressionHelidecksJettiesAircraft crash rescuePortable fire extinguishers

Medium expansionVapour suppressionFlammable liquid storage tank bundsSmall cable ductsSmall fires involving flammable liquids,such as those following road trafficaccidentsTransformer protection

High expansionKnockdown and extinction in, andprotection of, large volumes such as

t

High expansion finished foam flows directly outof the foam-making equipment and is not project­ed any appreciable distance. Its coverage of largeareas can also be slow but the immense quantity offoam produced (expansion ratios are sometimes inexcess of 1000: I) can quickly fill large enclosures.Often, flexible ducting is required to transport thefoam to the fire. Due to its volume and lightness,high expansion foam is more likely than low andmedium expansion foam to break up in moderate­ly strong wind conditions (Reference I).

The equipment used to produce secondary aspirat­ed foam is often standard water type branches andnozzles although there are some specificallydesigned nozzles available. The foam produced inthis way is not well worked, has a very low expan­sion ratio and short drainage time, and tends to bevery fluid. These properties, combined with thefilm-forming nature of the foam concentrates used,can result in a finished foam blanket that canquickly knockdown and extinguish fires of someliquid hydrocarbon fuels. This ability can makethem ideal for use in certain firefighting situations

6 Fire Sen'ice Manual Firejighting Foam 7

Firefig ting Foam h pt

Chapter 3 - Categories of Fire andFirefighting Foam

SecondaryAspiratedFinished Foams

Figure 2.4

LolV expansion.

Typical Effective

Projection: 2' metres

Figure 2.5

Medium expansion.

Typical Effective

Projection: 14 metres

Figure 2.6

High expansion.

Minimal Projection.

(Photos: Mid and West Wales

Fire Brigade)

)

.1 Cia, e, of ire

In the UK the standard classification of fire typesis defined in BS EN 2 : 1992 as follows:

Class A: fires involving solid materials, usuallyof an organic nature, in which combus­tion normally takes place with the for­mation of glowing embers.

Class B: fires involving liquids or liquefiablesolids.

Class C: fires involving gases.

Class D: fires involving metals.

Electrical fires are not included in this system ofclassification (see this Chapter, Section 2).

In the following Sections, the general principles ofextinguishment, particularly in relation to fire­fighting foams, are reviewed for each of the aboveclasses of fire.

(a) Class A fires

Class A fires are those which involve solid materi­als usually of an organic nature such as wood,cloth, paper, rubber and many plastics.

Some manufacturers of AFFF, AFFF-AR, FFFP,FFFP-AR and SYNDET foams state that theirproducts may be used as wetting agents at between0.1 % and 3% concentration to assist in the extinc­tion of class A fires. For these fires, AFFF, AFFF­AR. FFFP and FFFP-AR may be used at low andmedium expansion while SYNDET foams may beused at low, medium or high expansion.

There are said to be advantages in the use of wet­ting agents when fires become deep seated. Inthese conditions, water can be slow to penetrate. A

wetting agent that reduces the surface tension ofwater is claimed to greatly improve penetration tothe seat of these types of fire. When a wettingagent is employed, a deep seated fire is predomi­nantly extinguished by the cooling effect of thewater mix rather than by the smothering effect ofany foam that may be produced.

Surfactant based foams display some wettingagent properties, but are more expensive thanproducts sold purely for their wetting agent char­acteristics. From time to time, a few brigades takeadvantage of these wetting agent properties byusing AFFF not only for class B fires (see (b)below), but also, they claim, to make better use oflimited water supplies on Class A fires. It isclaimed that the increased cost in agent is oftenjustified by reduced water damage to the property.

Tests have indicated that in some circumstancesthe addition of some foam concentrates to watercan help in reducing the severity of a Class A firewhen compared to the use of water alone(Reference 2). In particular, when applied by sprayto wooden crib fires, secondary aspirated AFFF,and to a slightly lesser extent, FFFP, AFFF-AR andSYNDET, performed significantly better thanwater. Several wetting agents were also tested butthey did not perform much better than water. Theseresults seem to indicate that wetting propertiesmay not alone quickly and effectively deal withClass A fires involving wood. The smotheringcharacteristics of the foams may also be helping.(In fact, this is the principle under which American'Class A' foams have been developed).

During these tests, because of the size and shape ofthe fires, some areas of the cribs were not ade­quately reached by the spray. Consequently, testswere also performed using jet applications ofwater, primary aspirated AFFF and secondary

..

8 Fire Service MWIl/(/! Firefighting Foam 9

aspirated AFFF. There was little difference in thefirefighting performances of these indicating thatif adequate amounts of water can be applied to allareas of a wood fire, it will perform just as well asa primary aspirated or secondary aspirated foamwhen used in the same conditions.

Medium and high expansion foam have beenadvocated for indoor use on class A fires. The con­finement provided by the walls of buildings allowsthe foam to accumulate into a thick blanket andalso protects the foam from being torn apart bywind. The mechanism put forward for extinguish­ment is that the foam cuts down the movement ofair which supports combustion. There is a coolingeffect as water from the foam evaporates, and thesteam generated will also tend to reduce the oxy­gen level in the air surrounding the fire. If the foamblanket is deep enough, it will exert enough down­ward pressure to enable it to refill holes opened upwhen the foam is destroyed by the heat from thefire. Materials and structural members that wouldotherwise be exposed are shielded from heat radi­ation by the foam.

Although high expansion foam can be effective,the main practical drawback is that firefighterscannot be sure that the fire has been extinguished(see Chapter 5, Section 4). It can be dangerous toenter a deep foam blanket to track down the seat ofa fire since there is a chance of sudden exposure toheat and products of combustion. Under someconditions, the fire can continue to burn for a con­siderable period at a reduced rate supported by theair released from the foam as it breaks down.

The use of medium expansion foam against indoorclass A fires, such as in warehouses, could be amore effective and efficient use of foam. It shouldbe possible to restrict the foam application so thatthe area of origin of the fire is kept under observa­tion whilst maintaining sufficient foam flow toforce the foam onto the fire.

(b) Class B Fires

(i) General

Class B fires are those which involve flammableliquids, liquefiable solids, oils, greases, tars, oilbased paints and lacquers (i.e. flammable and

combustible liquids). Combustion of these occursentirely in the vapour that is present above the sur­face of the liquid. For firefighting purposes, ClassB liquids can be subdivided into three categories,each requiring different properties from firefight­ing foams in order to achieve effective and effi­cient fire control and extinction.

The categories are:

• high flash point water-immiscible Class Bliquids;

• low flash point water-immiscible Class Bliquids:

• water-miscible Class B liquids;

Some high flash point liquid hydrocarbon fires,such as those involving fuel oils, can, under verycontrolled conditions, be extinguished using onlythe cooling effect of water.

However, most low flash point hydrocarbon fires,such as those involving petrol, cannot be extin­guished by water alone as the fuel cannot be low­ered to a temperature where the quantity of vapourproduced is too small to sustain burning. In addi­tion, water is generally much denser than liquidhydrocarbons, consequently, when applied duringfirefighting, it immediately sinks below their sur­faces without having any beneficial effect, in fire­fighting terms, on the fire. In fact, the applicationof water may cause the surface area of the fire toincrease and spread to previously unaffected areas.

Foam is generally applied to both high and lowflash point hydrocarbon fuel fires because it pro­vides a visible blanket which controls and extin­guishes these fires faster and more effectively thanwater.

The three categories of Class B liquids and theirfirefighting characteristics are described in the fol­lowing Sections.

(ii) High Flash Point Water·immiscibleClass B Liquids

Water-immiscible liquids with high flash points, orclass C petroleum liquids, are those with a flash

point above 55°C such as gas oils, sbme diesel oils,heavy fuel oils and heavy lubricating oils. At nor­mal ambient temperatures these liquids have lowvapour pressures and so do not generate flamma­ble concentrations of vapour.

Water spray can be used to extinguish fires in highflash point liquids since the cooling effect of wateris sufficient to reduce the generation of vapour tobelow the concentration needed to sustain com­bustion.

Firefighting foams are very effective against thistype of fire giving very rapid control and securityagainst reignition, however, use of water spray canbe perfectly satisfactory and far less expensive inmany cases.

The primary mechanisms by which foams extin­guish high flash point liquid fires is by cooling theliquid surface and cutting out back radiation fromthe flames. The smothering action of foam plays arelatively insignificant role.

(iii) Low Flash Point Water-immiscibleClass B Liquids

Water-immiscible liquids with low flash points, orclass A and B petroleum liquids, have flash pointsbelow 21°C and 5SOC respectively. These includeclass A petroleum liquids such as aviation gaso­line, benzene, crude oil, hexane, toluene and petrol(including lead-free), and class B petroleum liq­uids such as avtur jet fuel and white spirit.

Spills or pools of low flash point liquids can pro­duce flammable vapour under normal ambienttemperatures, and flammable or explosive concen­trations can accumulate at low level, since most ofthe vapour will be heavier than air.

Water sprays are unsuccessful in extinguishingfires in low flash point liquids because vapour gen­eration is not sufficiently reduced by the degree ofcooling achieved. However, considerable reduc­tions in flame height and radiation intensity can beachieved with water spray application. Obviously,care should be taken to ensure that the fuel doesnot overflow any containment. Where the fuel isnot contained, the application of water will resultin further fuel and fire spread.

Firefighting foams are effective on low flash pointliquids because they trap the vapour at, or justabove, the liquid surface. The trapped vapour thensets up an equilibrium with the liquid which pre­vents further vapour generation. Where deep foamblankets can be formed, such as in storage tankswith a large ullage, this process may be assisted bythe increased pressure exerted by the heavier blan­ket. Film-forming foams produce a thin film on thesurface of some of these class B liquids which mayalso prevent vapour escaping.

Additional benefits of using firefighting foams onthese liquids are that they cool the liquid surface,reduce the vapour generation rate, obstruct radia­tion from the flame to the liquid surface and reducethe oxygen leveL by the production of steam, wherethe foam, flame and liquid surface meet.

Lead, as lead tetra-ethyl (or lead tetra-methyl) hasbeen used for more than 60 years to improve thepelformance (octane rating) of the hydrocarbonmixtures that constitute petrol. However, since[974, health and environmental concerns have

Figure 3./ Large scale leSI in progress.

(PhOfO: Fire E.\perirnenlal VIIi' J

10 Fire Service ManualFirejighling Foam 11

resulted in the progressive reduction in theamounts of lead in petrol. This reduction of thelead content has led to the use of oxygenates, forexample ethers and alcohols. as alternative octaneimprovers. Oxygenates are only used in eitherleaded or lead-free fuels when the octane ratingcannot be achieved cost effectively by refineryprocesses.

Large scale fire tests have been carried out in theUK to establish whether lead-free petrol, conform­ing with current British and European standards.would present any problems to the fire serviceusing their standard low expansion foam equip­ment and techniques (Reference 3). The resultsshowed that providing brigades follow the HomeOffice recommended minimum application rates(see Chapter 4), no problems would be expectedwhen using good quality AFFF or FFFP againstpetrol formulations permitted by current and like­ly future standards. However, FP gave poor extinc­tion pert'ormances against lead-free petrols con­taining oxygenates although its burnback pelfor­mances were better than either AFFF or FFFP.

In recent years liquefied flammable gases havebecome an increasingly important source of fuel incommerce and industry. Increased use bringsincreased transportation of these liquids through­out the country by road, rail, and in UK coastalwaters, which in turn increases the possibility ofaccidental spillage. The product group includesLPG (Liquefied Petroleum Gas, usually propaneor butane) liquid ethylene and LNG (LiquefiedNatural Gas, i.e. methane).

Boiling points for these liquefied gases are lowand so in the event of spillage, rapid vapour pro­duction occurs. Due to the greater amounts ofvapour produced and the low buoyancy of coldvapour, the dispersal of this vapour is more prob­lematical than from spilled flammable liquids suchas petrol. In still air conditions, and where theground is sloped or channelled. this vapour cantravel long distances from its source. Liquefied gasvapour has been known to travel 1,500 metresfrom a spilled pool of liquid whilst retaining a con­centration above the lower flammability limit.

phosphorous pentoxide. Other metal fires are treat­ed as class A fires, but in general the use of mediaother than foam or water is found to be more suit­able.

3.2 Electrica Fires

Firefighting foams are unsuitable for use on firesinvolving energised electrical equipment. Otherextinguishing media are available. Fires in de­energised electrical equipment are treated as eitherclass A or B as appropriate (see this Chapter,Section I).

3.3 Types of Liquid Fuel F're

(a) General

The classes of fire discussed in the previousSection have a strong bearing on the tactics andtechniques of using firefighting foam. However,the size, shape and general appearance of a fire isalso of particular importance when tackling class

B or class C fires. Firefighters often refer to spillfires, pool fires and running fires and the variationsin firefighting technique required to tackle each.This Section describes these types of fire and howtheir characteristics can affect the approach to fire­fighting.

These descriptions relate to ideal conditions whichin practice are unlikely to occur exactly asdescribed and in some situations, such as incidentsinvolving aircraft, more than one of these situa­tions may occur simultaneously. Even so, theyillustrate the principles involved.

(b) Spill Fires

Spill fires occur in unconfined areas oftlammable,or combustible liquids with an average depth ofaround 25mm or less. There is often variation inthe depth of the spill due to unevenness of the sur­face on which the liquid stands. Because it isunconfined, a spill fire may cover a very largearea.

(iv) Water-miscible Class B Liquids

Polar solvents and hydrocarbon liquids that aresoluble in water (water-miscible) can dissolve nor­mal firefighting foams. Such liquids include somepetrol/alcohol mixtures (see above), methyl andethyl alcohoL acrylonitrile. ethyl acetate, methylethyl ketone, acetone, butyl alcohol, isopropylether, isopropyl alcohol and many others.

Water-miscible class B liquids, such as some polarsolvents, require the use of alcohol resistant typefoam concentrates for firefighting and for vapoursuppression. These foams form a polymer mem­brane between the water-miscible and the foamblanket which virtually stops the destruction of thefoam and allows vapour suppression and coolingto continue. Alcohol resistant foam concentrateslose effectiveness unless they are applied gently tothe surface of polar liquids, avoiding plunging (seeChapter 5, Section 2).

(c) Class C Fires

Class C fires are those involving gases or liquefiedgases.

Medium and high expansion foams are suitable forliquefied gas spills both for fire extinguishmentand vapour suppression. The surface of the foam incontact with the liquid forms an icy slush whichinsulates and protects the upper layers of foam,and which in turn acts by reducing the evaporationrate from the liquid. A further important advantageis the relatively low amount of heat transmitted tothe liquid by water draining from medium andhigh expansion foams.

Low expansion foam is not suitable since itincreases the rate of evaporation from the liquid.For a liquefied gas spillage any reduction in therate of evaporation of the liquid is beneficial inthat it limits the size of the flammable (or explo­sive) cloud generated and hence reduces the possi­bility of ignition.

(d) Class D Fires

Class 0 fires are those which involve combustiblemetals such as magnesium, titanium, zirconium,sodium, potassium and lithium. Firefighting foamsshould not be used with water reactive metals suchas sodium and potassium, nor with other waterreactive chemicals such as triethyl aluminium and

Figure 3.2 Foam in use following de-energising of Iron.lformel: (NOle posilion of sand 10 conIC/in spillage.)(PhOlo: NOr/hem Irl'lolld Fire Brigade)

..

12 Fire Service Manllal

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Firefighlinf{ Foam ] 3

The main characteristic of spill fires is their rela­tively short burning times. If an average burn rateof 4mm of the depth of fuel per minute is assumed,then most of the fuel involved in a spill fire willhave burnt away within 7 minutes of ignition. Suchbrief burn times are. however. unlikely to occur inpractice. Flammable liquid may remain in a rup­tured fuel container and burn for a considerabletime. continuous leakage may replenish the spill ornumerous deep localised burning pools of fuelmay form over a large area.

(c) Pool Fires

Pool fires occur in confined pools of flammable, orcombustible, liquids which are deeper than 25mmbut not as deep as the contents of storage tanks. Apool fire may cover a large area depending on thevolume of the fuel source and the area of the con­fined space. It may take the form of a bunded areain a tank farm or a hollow pit or trench withinwhich flammable liquid has collected from a rup­tured process vessel, road or rail tanker.

The difference between pool fires and spill fires isthat pools may, depending on depth. continue toburn for a considerable period of time. As a result,firefighters are more likely to encounter a welldeveloped fire burning evenly over a large area.rather than the more isolated, scattered fires whichare characteristic of an unconfined spill. Foammay also be subject to more fuel contamination ifforceful application is used due to the depth of thefuel. Consequently techniques. such as playing thefoam stream agai nst a sol id surface and allowingthe foam to run onto the fire, may be both desirableand a practical possibility if suitable surfaces areavailable (see Chapter 5, Section 2).

The sustained high levels of heat output maydemand more effort to be made in cooling exposedstructures both to minimise damage during the fireand to prevent reignition after extinguishment. Itshould be remembered that if water is used forcooling. it will break down any existing foam blan­ket in that area, allowing any remaining flames toburn back and preventing further blanket forma­tion until the water application ceases.

The pool fire. therefore. requires a foam with ahigh fuel tolerance and heat resistance as well as

fast flowing characteristics. Adequate post firesecurity is also required.

(d) Spreading Fires

Spreading fires can be described as unconfinedspill or pool fires in which the liquid fuel is beingcontinuously supplemented by a spray, jet orstream from a ruptured tank or equipment. Thecontinuous supply of fuel often results in burningliquid flowing into inaccessible areas, such asdrainage systems and floor voids.

An early step in fighting a spreading fire is to stopthe flow of product to the flames whenever possi­ble. Water spray provides an excellent screenbehind which to approach the fire and close leak­ing valves for instance. The flow from a storagevessel can also be stopped by water displacementif there is sufficient ullage above the source of theleak. This method has been successful in the caseof a ruptured storage tank line. Water is pumpedinto the tank to raise the liquid fuel above the levelof the outlet line so that water, instead of product,flows from the broken line.

[f the flammable liquid is a high flash point fuel.the burn back rate of flames through the spray, jetor stream of fuel leaking from the container maybe less than the rate at which the fuel is dischargefrom the leak. In this situation, the discharging fuelwill not be on fire. Consequently, the fire can beextinguished with a foam blanket or water spray ina similar fashion to a pool fire, the only additionalprecaution being to ensure that the level of fueldoes not rise sufficiently to over spill the contain­ment. Sand bagging, diversion channels andpumping out are all useful techniques to help pre­vent breakdown of containment.

If, on the other hand, the burn back rate of flamesthrough the spray, jet or stream of fuel leakingfrom the container exceeds the rate at which thefuel is coming out of the container, then the dis­charging fuel will also be on fire. It may be neces­sary to use dry powder to extinguish fires in flow­ing jets of liquid or gas in conjunction with foamapplication to the spreading fuel. Water sprays areeffective in reducing the heat output from burningjets although they will break down any foam blan­ket already formed.

(e) Running Fires

This term refers to the case when a burning liquidis moving down a slope on a broad front. The situ­ation is rare but extremely hazardous because ofthe rapidity with which objects and people in thepath of the flow can be enveloped. It is not possi­ble to advise any course of action other than rapidevacuation from the oncoming flow. If monitorsand hoses are immediately available they couldprovide sufficiently rapid knockdown.

On some fuels, film-forming foams are consideredparticularly effecti ve at fast knockdown. althoughother foams can have similarly rapid effects.Another technique is to lay a band of foam at thelower end of the path of flow so that any pool thatbuilds up will do so beneath a foam blanket. Forthis type of application fluoroprotein or film-form­ing alcohol resistant foams might be consideredmost suitable because of their stability. althoughother foams would also satisfactorily perform thetask.

The main method of combating running fires is byprevention. Firefighters must be aware of anypotential for a pool fire to breach or over spill itscontainment. Firefighting efforts should be adjust­ed to reduce such a risk. for example, minimisingthe use of cooling water which could drain into thecontained pool and cause overflowing, monitoringthe integrity of containing bund walls and evacuat­ing in advance any area which could possiblybecome inundated.

(I) Other Terms

Various other terms are used for different types offire and explosion incident such as BLEVE (seeGlossary of Terms - Firefighting Foams, at therear of this Volume), vapour cloud explosion, gasflare, etc. These have not been covered separatelysince the use of firefighting foam is not directlyinvolved.

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14 Fire Service Manual

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Firejighling Foam 15

Firefighting Foam

Chapter 4 - Recommended MinimumApplication Rates

Ch pt r

4.1 General

The application rate of a foam onto a fire is nor­mally expressed as the amount of foam solution, inlitres per minute, to be applied to every squaremetre of the total area to be covered with foam.

The Recommended Minimum Application Rate isthe minimum rate at which foam solution is recom­mended to be applied to a fire. The rate assumesthat all of the foam made from the foam solutionactually reaches the surface of the burning fuel.

The recommended minimum application rateincludes a 'safety margin' to help to take intoaccount factors such as:

• variations in the quality of foamconcentrate;

immiscible class B liquids. Also, reconunended dura­tions of foam application are included in the tables.

It should be noted that the figures given in Tables4. J and 4.2 relate to minimum foam solution appli­cation rates and times and assumes that all of thefinished foam produced from the foam solutionactually reaches the surface of the liquid on fire.These rates should not be considered as beingdefinitive; allowances must be made to compen­sate for losses due to circumstances such as fall outof finished foam from the foam stream, adverseweather conditions, breakdown of foam due toflames before it reaches the fuel surface, and lossof foam due to the thermal convection currentscaused by the fire. For storage tank fires, theserates need to be increased by up to 60% to accountfor foam losses.

• variations in the quality of finishedfoam produced;

In addition, it is recommended that applicationrates should be reviewed if, after 20-30 minutesappJication, there has been no noticeabJe reductionin the intensity of the fire.

) )

• some of the detrimental effects offorceful application.

The Home Office recommended minimum appli­cation rates for use by the UK fire service for firesinvolving water-immiscible class B liquids aregiven in Section 2 below. Advice is given concern­ing the application rates for fires involving water­miscible class B liquids in Section 3 below.

4.2 Fires Involving Water­immi cible Clas B Liquid

Tables 4. I and 4.2 give the minimum applicationrates of foam soJution recommended by the HomeOffice for use by the UK fire service when usingmanual firefighting equipment to apply low andmedium expansion foam to tires involving water-

In practice, the recommended minimum applica­tion rates are of great importance in pre-planningthe resources needed for a foam attack. It has adirect bearing on the quantity of concentrate, andwater required, and also should dictate the amountof delivery equipment, i.e. appliances, monitors,branches, proportioners and hoses.

4.3 Fire Involving Wa er O1i IblCia s B Liquid

Application rates for water-miscible fuels varyconsiderably depending on the following factors:

• the type of fuel;

• the depth of fuel;

Firefighting Foam 17

Table 4.2: Home Office Recommended Minimum Application Rates Of Foam Solution For theProduction of Medium Expansion Foam For Use on Liquid Hydrocarbon Fuel (Class B) Fires

Table 4.1: Home Office Recommended Minimum Application Rates of Foam Solution For theProduction of Low Expansion Foam For Use on Liquid Hydrocarbon Fuel (Class B) Fires

Minimum Application Rate of Foam Solution Minimum Application Time(lpm/m2) (Minutes)

----------------

the type of foam;

the manufacturer of the foam;

the method of foam application.

Some of the most widely used water-miscibleliquids include:

Due to the large number of water-miscible fuels inuse, and the varying firefighting performance ofdifferent foams on each of them, information onthe recommended application rates for a particu larwater-miscible risk should be obtained from themanufacturer of the alcohol resistant foam concen­trate to be used.

Alcohols (e.g. Methanol, Ethanol,Isopropanol)

Ketones (e.g. Acetone, Methyl EthylKetone)

Vinyl AcetateAcrylonitrile

Typical recommended foam application rates forwater-miscible liquid fires range between 4 and 13litres per minute per square metre. However, it isrecommended that the minimum application timefor a spill of water-miscible fuel should be 15 min­utes and for tanks involving these fuels it shouldbe a minimum of 60 minutes.

••

•Tanks TanksFuel FuelFlashpoint Flashpoint>40°C <=40°C/

Bund

15 NR NR

15 45 60

15 45 60

15 45 60

15 45 60

15 45 60

Spill

Minimum Application Time(Minutes)

TanksD>=81m

TanksD>=45mD<81m

NR NR NR

8.0 9.0 10.0

6.5 7.3 8.1

6.5 7.3 8.1

6.5 7.3 8.1

6.5 7.3 8.1

<=- less than or equal to>= - more than or equal toIpm/m 2 - litres per minute offoam solutionper square metre of hurning area offireNR Not Recommendedji)r this use

5.0

4.0

4.0

4.0

6.5

4.0

SpilllBund TanksD<45m

Minimum Application Rate of Foam Solution(Ipm/m2)

Protein

AFFF-AR

Foam Type

Fluoroprotein

FFFP

AFFF

m - metre

Notes to Table 4. I< - less than> - More thanD - Diameter of tank

FFFP-AR

Foam Type

SYNDET

FI uoroprotei n

AFFF

FFFP

AFFF-AR

FFFP-AR

Spill/Bund

6.5

5.0

4.0

4.0

4.0

4.0

Spill Bund

15 60

15 60

l5 60

15 60

15 60

15 60

On water-miscible liquids. application must besuch that the foam blanket is delivered gently ontothe liquid surface without submerging the foam oragitating the liquid surface (see Chapter 5, Section2). If some submergence and agitation is unavoid­able, the foam blanket will be destroyed at a highrate and much higher application rates and appli­cation times will be required.

Note to Tahle 4.2 :Ipm/m 2

- litres per minute offomn solution per square metre of huming area offire

18 Fire Service Manual Firefighting Foam 19

Firefig ting Foam

Chapter 5 - Operational Use of Foamon Class B Liquid Fuels

Cbapller

5.1 General

This Chapter mostly concerns the main fire serviceoperational use of foam, that is on class B liquidfuels.

mean that the firefighters will be able tostand as far away from the fire as is possiblebut, also, the wind wil.l cause the fire plumeto angle away from them and so furtherreduce the radiant heat being experienced bythem.

When using foam operationally, there are a num­ber of basic, common sense procedures that needto be followed to help to ensure success, these are:

• Objective of Foam Application: On arrivalat an incident, an immediate decision needsto be made on whether foam needs to beused and, if so, what is the objective that ishoped to be achieved by its application. Forinstance, is the objective to provide a tem­porary break in order to attempt a rescue orclose a valve, or is the objective to totallyextinguish the fire?

•

•

Collect Sufficient Resources: Before com­mencing foam application, ensure thatenough resources of foam, water, equip­ment, personnel etc. are collected togetherto enable the objective of foam applicationto be carried out successfully. Home Officerecommended minimum foam applicationrates (see Chapter 4) should. where possible,be used as the basis for calculations. If a fireis to be totally extinguished, then runningout of foam concentrate during applicationwill probably result in a complete re­involvement of the fire and completewastage of the resources already used.

Wind Direction: Obviously, foam can onlybe effective when it reaches the intendedtarget. Wherever possible, the foam streamshould be directed downwind in order toproject the foam over the maximum possibledistance. In fire situations, this will not only

•

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Correct Operation of Equipment: Thefoam-making equipment must be usedunder the correct operating conditions offlow and pressure. Inductors and foam-mak­ing branches must be matched and the cor­rect foam concentrate for the fuel and thecorrect foam induction rate must be chosen.Care should be taken not to cover the airinlet holes of the foam-making branchbecause this will result in poor quality foambeing produced.

Gentle Foam Application: Foam applica­tion should be as gentle as possible.Forceful application, which is applyingfoam directly to the surface of a fuel, willgenerally result in fuel contamination of thefoam, increased breakdown of the foam, andincreased flame intensity and radiated heatfrom the area of application due to vigorousdisturbance of the surface of the fuel. Theoverall effect will be a dramatic reduction inthe effectiveness of the foam. In addition,forceful application to an existing foamblanket may cause breaks which reveal theunderlying fuel. If complete extinction hasnot been achieved when this occurs, then asignificant amount of burnback could result.

Continuous Foam Application: Once foamapplication has commenced, it should con­tinue without interruption until at Ileast theobjective of the foam application has beenachieved. Interruptions in foam application

Firefighting Foam 21

(ii) Forceful Application

• finger/hand deflection application.

• gentle direct application;

• front sUIface indirect application;

• waJllobject indirect application;

Of these, the front surface and wall/object indirectmethods are likely to produce the most gentleapplications of foam to the fuel surface during nor­mal firefighting operations. The finger/handdeflection method is best suited for nearby appli­cation of foam to residual flames. Each of thesegentle application methods is described below:

• Gentle direct application involves applyingfoam to the surface of the fueL with the foam-mak­ing branch as far away from the fire as possible,

(Photo: A1id om) West Wales Fife Brigade)

of mixing of the foam with fuel causing the foamto become contaminated. Inevitably, some of thefuel within this contaminated foam will burn off,causing the partial destruction of the foam blanketas it does so.

Figure 5. J Low expansion foam-making branch in use.

In addition, when the foam stream hits the burningfuel, it causes a great deal of disturbance to the fuelsUlface which results in a considerable increase inflame intensity and hence radiant heat. This wi IIcause the partial breakdown of any existing foamblanket and also makes it very uncomfortable forthe firefighters to maintain their position.

(iii) Gentle Application

There are several gentle foam application tech­niques available which will reduce the impactvelocity of the foam stream. These are:

General

making capability should be maintained,resources replenished and remain ready forimmediate use until all hazards have beenremoved or neutralised.

(i)

• Beware of Ignition of the Foam Blanket:Even with a thick foam blanket in place,operations involving possible ignitionsources, such as hot cutting, should be car­ried out with great care. Fuel contaminationof foam can occur during application andthe vapour from some fuels will penetratethe foam blanket. Complete involvement ofthe foam blanket in flame can happen with­in seconds if a contaminated foam blanket isignited - this can occur with all types offoam concentrate. Foam production capabil­ity must be maintained throughout any suchoperations.

Further discussion of these basic and other proce­dures follows with particular reference to the typeof finished foam (i.e. Iow, medium or high) beingused.

(a) Primary Aspirated Foams

5.2 Low Expansion Foam

Low expansion foam-making branches throw theirfoam over much longer distances than medium orhigh expansion foam-making equipment. Thislength of throw is generally enough to allow fire­fighters to tackle large, open, liquid fuel fires whilestanding at a distance from the fire where the radi­ated heat is bearable.

Forceful application of the foam, such as whenaiming a foam stream directly onto the sUIface ofa burning fuel, causes the foam to impact heavilyon, and penetrate below, the surface of the fuel('Plunging'). This leads to a considerable amount

Ideally, the application of the foam to the sur­face of the fuel should be as gentle as possible inorder to achieve the most effective performancefrom the foam.

Edge Fires: Long after the main bulk of afire has been extinguished, flames are likelyto persist around the edges of the foam blan­ket where it meets and attempts to sealagainst objects, such as hot metal containerwalls. These last flames are likely to requirea great deal of time and foam to extinguish.If stocks of foam run out at this stage, thefire may burn back completely. Applicationshould continue to be as gentle as possible,with consideration being given to usingmedium expansion foam if access andequipment permit. It is often better to rein­force the foam blanket near to persistentflames so that it flows over the area of itsown accord. Using water to cool the exter­nal walls of a metal container around thearea of flame can help to reduce the rate ofvaporisation of the fuel, and hence the inten­sity of the flames. In addition, the cooler themetal walls of a container, the easier it willbe for a foam blanket to seal against them,suffocating the remaining flames as it doesso.

will result in wasted resources. The foamapplication should at least be maintained atthe Home Office recommended minimumapplication rate (see Chapter 4).

Maintaining the Foam Coverage: Once afire has been extinguished or a toxiclflam­mable fuel has been covered with a foamblanket, foam application should continueuntil a thick foam blanket has been built up.However, the foam blanket will break downand loose its water content with time.Consequently it is important that the foamblanket is regularly replenished in order toensure continued protection from re-ignitionor vapour release. Where possible, the useof water jets or sprays should be avoided inthe vicinity of a foam blanket as these canalso cause the foam to break down.

Maintain Foam-making Capability: Evenafter the fire has been extinguished (or thevapour from flammable and/or toxic mater­ial has been suppressed) and a thick foamblanket has been built up, a significant haz­ard still remains. Consequently, the foam-

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22 Fire Service Manual Firejighting Foam 23

using the full trajectory of the foam stream. Thisreduces the impact velocity of the foam due to theloss of speed of the foam stream as it travels throughthe air and the dispersion of the foam in the streamduring transit.

Another similar method is known as the 'rain­down' technique. This involves directing the foamstream almost vertically up into the air so thatwhen the foam stream reaches its maximumheight, it breaks up and the resulting chunks offoam 'raindown' onto the fire. This has two poten­tially serious drawbacks; the first is that any ther­mal updraft from the fire plume is likely to carrythe foam upwards and away from the surface ofthe fuel; the second is that the technique requiresthe foam-making branch, and the firefighter, to bepositioned relatively near to the fire.

• Front surface indirect application involvesfoam being rolled or pushed onto the surface of thefuel by aiming the foam stream at a point in frontof the fuel and allowing the foam to build up. Withfurther applications of foam to this area, a raft offoam will begin to gently flow across the surfaceof the fuel. This method leads to very little fuelcontamination of the foam.

• Wall/object indirect application involvesaiming the foam stream at a surface behind the fire(such as the sides of a storage tank) or at an objectin, or to the side, of the fire. By positioning thebranch at a suitable distance away from the object,the foam stream will have lost much of its energyby the time it hits the object. Further energy will belost on impact with the object with the result thatthe foam will slide slowly down the object andgently onto the surface of the fuel. A raft of foamwill form which, with further application of foamto the object. will increase in size and spread overthe surface of the burning fuel. This method hasthe additional advantage that it can be used to coolhot metal objects which might otherwise causeedge sealing problems.

• Finger/hand deflection application invol vesthe firefighter placing his hand or fingers directly infront of the outlet nozzle of the foam-makingbranch so that the foam issues as a spray rather thana jet: greatly reducing the impact velocity of thefoam. This method is most suited to extinguishing

small residual fires from very close range. Onedrawback of this method is that it may disturb theexisting foam blanket and reveal some of theunderlying fuel.

Suitable hand protection must be worn. This tech­nique is not acceptable for use with large through­put foam-making branches where fingers may bebent back by the force of the foam stream. Careshould also be taken when using long foam-mak­ing branches to ensure that the firefighter is not putoff balance by trying to use this technique.'Blabber-mouth' foam-making branches haveflaps that can be opened and closed at the outletend of the nozzle. These deflect the foam stream inmuch the same way as when using this method offoam application.

(iv) Single Point of Application

In order to achieve a quick flame knockdown withthe minimum of foam with a single branch, foamshould only be applied to one point and the branchshould be held still. This will allow a foam raft (or'bite') to form which will then spread over the sur­face of the fuel.

Moving the branch will result in many smallerapplications of foam which will not sufficientlycool the fuel locally or suppress the fire to allow anadequate foam blanket to form. This will lead to agreat deal of foam destruction, and hence wastage,of the finished foam.

When using more than one branch, a single pointof application should stiJl be used wherever possi­ble.

However, it should be noted that foam will onlyflow over a liquid fuel a maximum distance of 30metres from the edge of the foam application area(see Chapter 7, Section 5b(x)). Consequently,where the fire area is very large, several foamapplication points, and hence branches, will berequired. In such cases, the number of applicationpoints should be kept to the absolute minimum thatallows the foam blanket to cover the whole of thefire area.

One method of assisting in the spreading of foamover the surface of a fuel once a bite has been

achieved is by producing a swirling motion inthe whole surface area of the fuel. This can bedone by moving the branch or branches so that thestream(s) lands slightly off centre of the liquid sur­face (see Chapter 7, Section 5b) (xi»).

(v) Assistance Required to Apply FoamAccurately

Usually, when applying low expansion foam, thefirefighter at the foam-making equipment will beunable to see where the foam stream is landing.Consequently, the firefighter may require helpfrom someone standing to the side who can seewhere the foam is being applied and can indicate,perhaps by the use of a radio or arm signals, whatmovements to the foam stream the firefighter mustmake in order to ensure the required applicationcan be achieved.

(vi) Extinction of Residual Flames

As mentioned previously, the extinction of anyresidual flames should, where possible, be by :

• the use of medium expansion foam;

• foam applied using the finger/hand deflec­tion application technique;

• the gentle application of foam to the sur­rounding foam blanket in order to allowexisting foam to flow over the flames.

Some combination foam-making branches areavailable that allow the operator to easily switchfrom low expansion to medium expansion foam,these have obvious applications here. However,tests carried out by the Home Office FROG on onecombination 225 litre per minute foam-makingbranch indicated that it produced very poor lowexpansion foam which was unable to sufficientlycontrol a 56m2 petrol fire. Consequently, the fire­fighter was unable to get close enough to the firein order to use the medium expansion capability.

Forceful application of low expansion foam toresidual flames should be avoided due to the like­ly disturbance of the existing foam blanket whichmay reveal larger areas of underlying fuel and pos­sible re-ignition.

(vii) Continued Application After Extinction

Foam application should always continue afterextinction in order to produce a very thick protec­tive foam layer. It can take less than 4 minutes forhalf of the liquid content of a foam blanket to drainout. This may not have any effect on the appear­ance of the blanket but the loss of this amount ofwater will make the blanket less resistant to burn­back, less able to seal any breaks that may occur inthe blanket, more likely to allow vapour to perco­late through it, and make it more susceptible tobeing blown away by wind. Consequently, it isessential that the foam blanket is replenished atregular periods in order to maintain its effective­ness.

When replenishing, care should be taken to avoidapplying water initially to the foam blanket.Applying water will break down the foam blanket,cause gaps in the blanket to reveal the underlyingfuel and, in some situations, may produce a staticdischarge that could reignite the fire.

(viii) Precautions to Prevent Ignition of theFoam Blanket

Precautions should be taken to ensure that an igni­tion source does not come into contact with thefoam blanket. Rescue operations that take placewithin the foam blanket will inevitably lead tomuch disturbance of the foam blanket and furtherfuel contamination. Should foam that has beencontaminated with fuel ignite, then large areas ofthe foam blanket are likely to become involved inintense flames within seconds. These flames wjllprobably die down relatively quickly but leavingthe upper layer of foam badly damaged. Generally,the shorter and more forceful the foam application,the more severe any resulting fire is likely to be.

Crews should be on constantshmdby while operations takeplace to ensurc that adequatefoam and firefighting cover aremaintaincd. Should ignition uccur,the response must be immediate.

24 Fire Service Manual Firefighting Foam 25

Figure 5.2 Primary aspirated foam in use.

rPhoto: WeSl Midlands Fire Service)

(ix) Ignition of Fuels Due to the StaticDischarge During FoamlWaterApplication

There have been several reports of floating rooftank fires that may have been ignited by the dis­charge of static electricity that had been generatedby the over-the-top application of water and/orfoam to refined hydrocarbon liquids (e.g. naphtha)following the sinking of the roof.

As a precaution, if foam is to be applied to a largehydrocarbon storage tank (greater than 500m3

)

where the roof is no longer present, and there is arisk of ignition of the contents of the tank, thenfoam should be applied via the sides of the tank.This gentle application method will allow foam toflow down on to the surface of the fuel and form acontinuous raft of foam. Islands of foam that arenot attached to the main raft should be avoidedbecause these may cause a static discharge whenthey reach the tank sides.

The impact of water or foam streams directlyon the tank contents should also be avoided asthis may produce a static discharge.

(b) Secondary Aspirated Foams

(i) General

At low expansion, film-forming foams (e.g. AFFF,AFFF-AR, FFFP, FFFP-AR) can be applied prima­ry aspirated, with the techniques described above,or they can be applied secondary aspirated. Onlyfilm-forming foams can be applied secondary aspi­rated, non film-forming foams such as P, FP andSYNDET must not be applied in this way.

(H) Application Techniques

Film-forming foams can be applied secondaryaspirated by using standard water-delivery branch­es set to wide angle spray or fog. The use of sprayor fog produces a relatively gentle application and,

on some fuels, this will allow a film to form on thesurface of the fuel.

Application should be made directly to the surfaceof the burning fuel. This requires the firefighter toget very near to the fire although a suitable spraypattern should provide sufficient protection fromradiant heat. The method of application generallyrecommended is to spray the secondary aspiratedfoam across the burning fuel with a sweepingaction, back and forth.

See Section (iv) below regarding the applicationtechnique when using purpose designed secondaryaspirated foam making branches.

(iH) Limitations of Use

The expansion of secondary aspirated foam is verylow, generally less than 5. On some fuels fires, itsuse can result in very quick control and extinc­tions. However, tests have indicated that secondaryaspirated film-forming foams can take up to twiceas long to extinguish a petrol spill fire as that takenby the same film-forming foams when used prima­ry aspirated (Reference 4).

On some of the more volatile hydrocarbons(including some blends of petrol), secondary aspi­rated foam has limited security and burnback resis­tance. Consequently, it should not be used forvapour suppression. If possible, after its use toextinguish a fire, a primary aspirated foam blanketshould be applied to provide adequate burnbackprotection.

Secondary aspirated foam is not suitable for use onwater-miscible fuels, even when alcohol resistantfilm-forming foam concentrates are employed.

(iv) Use in Specialised FirefightingEquipment

Some purpose designed secondary aspirated foam­making branches have been designed for use inprocess areas and/or for incidents involving largestorage tanks. This equipment is claimed to throwfoam solution over a greater distance, and up to agreater height, than is possible with primary aspi­rating equipment. This makes this type of equip­ment suitable for the protection of large storage

tanks. However, with this type of equipment, bythe time the foam solution has been projected to itstarget, its expansion ratio can be of the order of 4: Ito 6: I. Consequently, application techniquesshould, where possible, be as those given abovefor primary aspirated foam.

(c) Water-miscible Fuels

Only primary aspirated alcohol resistant typefoams should be used to fight fires that involvewater-miscible fuels. These should be applied asgently as possible to the fuel surface using thetechniques described in this Chapter, Section 2.Forceful application of alcohol resistant foams towater-miscible fuels will drastically reduce theirfirefighting capabilities due to contaminationwhich will quickly break down the finished foam.Non-alcohol resistant foams such as AFFF, FFFP,FP and so on, should not be used on these types offuels because the finished foam disintegrates oncontact with the fuels.

(d) Large Fuel Storage Tanks

For many years, the recommended technique forthe application of foam to fully involved largestorage tank fires required a number of foam-mak­ing monitors to be positioned around the tank, eachapplying foam to a small area. This technique wasknown as 'surround and drown'.

This required long periods of foam applicationbefore sufficient cooling of the fuel and knock­down of the flames occurred to allow small areas offoam to become visible on the surface of the fuel.

This technique has now been mostly rejected infavour of applying large quantities of foam to asmall area of the burning fuel surface. This pro­vides a very high localised foam application ratewhich relatively quickly results in the localisedknockdown of flames and the formation of a raft offoam (or 'bite') in the foam application area. Onceformed, this raft of foam gradually enlarges andspreads across the surface of the fuel. The maxi­mum distance this will spread is 30 metres in alldirections (see Chapter 7, Section 5b(x» from theedge of the foam application area. Consequently,when fighting fires with large fuel surface areas,more than one main foam application point will be

26 Fire Service Manual Firefighting Foam 27

needed in order to ensure that the rafts of foamformed meet and hence cover the whole of the areaof fuel. The number of monitors this requires willobviously depend on their capacity but should alsotake in to account the maximum foam spread dis­tance of 30 metres. The aim should be to use theminimum number of foam application points pos­sible and, where necessary, several monitors canbe positioned to apply foam to the same point onthe fuel surface.

Once a bite has been achieved, the spread of foamacross the surface of the fuel can be aided by caus­ing the fuel to slowly swirl around the tank. Thismovement can be achieved by allowing the streamfrom a monitor to land slightly off centre of thefuel surface (see Chapter 7, Section 5b) (xi)).

5.3 Medium Expansion Foam

(a) General

Medium expansion foam can have relatively lowstability and poor burn back resistance and it is thesheer volume of foam produced, combined with itsinherent gentle application, that makes it an effi­cient and effective firefighting medium.

Figure 5.3 Medium expansion/oam in use i/1 a tank bUild.(PholO: A1id and We.\'{ ~yl/('s Fire Brigade)

For example, MX foam has a much greater volumethan low expansion foam. From the same amountof foam solution, a medium expansion foam gener­ator producing finished foam with an expansionratio of 100: 1 creates 10 times more finished foamthan a low expansion foam-making branch produc­ing foam of an expansion of 10: 1. Typically, medi­um expansion foam-making equipment producesfoam of expansions of between 50 and 100: l.

In order to make medium expansion foam, largequantities of air need to be mixed with the foamsolution. This mixing takes place within the foam­making equipment and this greatly reduces thespeed at which the foam emerges from it.

As a result, using medium expansion foam againstlarge fires can require firefighters to approach veryclose to the flames, exposing them to dangerouslevels of radiated heat. The risk to firefighters canbe reduced by the use of tloor standing mediumexpansion foam generators which, once in posi­tion, can be left unattended. It should be noted thathand-held medium expansion foam-making gener­ators should not be put on the ground while oper­ating because they may suck in debris which couldblock or break the internal foam-making mesh.

I II

The very gentle application characteristics and highvolume output of medium expansion foam makes itparticularly useful for rapid vapour suppression ofhydrocarbon liquids (and water-miscible liquidswhen using alcohol resistant film-folTIling foamconcentrates). It can also be used to fill, up to a max­imum height of around 3 metres, small volumessuch as those found in engine test cells and trans­former rooms.

The most common type of concentrate used to producemedium expansion foam is standard SYNDET,although FP and film-forming foams may also be used.

The Home Office recommended minimum appli­cation rates for medium expansion foam are virtu­ally the same as those for low expansion foamwhen used on hydrocarbon liquid fuel fires (seeChapter 4). However, Protein foam concentratemust not be used for the production of mediumexpansion foam and the limited throw of mediumexpansion foam is among the reasons why it can­not be used to fight large storage tank fires.

Medium expansion FP foam has been successful incontrolling crude oil bund fires with long pre-burntimes. The disadvantage of using medium expan­sion foams in these circumstances is that they donot release their water content quickly and there­fore their cooling ability is limited. Other disad­vantages of the use of medium expansion foam arethat they do not flow well, particularly in verywindy conditions and their heat resistance andability to seal against hot surfaces is also poor.

(b) Application Technique

To achieve the best possible fire knockdown,medium expansion foam should be applied in frontof a liquid pool fire and an initial foam raft ('bite')should be formed with little movement of thebranch. Further application of foam should then bethen be used to widen the raft to allow it to spreadover the surface of the fuel. This further applica­tion of foam should be to the edges of the raft, itshould not be to the flames in front of the raft.

(c) Use as a Fire Break

The Forestry Commission has experimented withthe use of MX foam in laying a barrier to grass,

heath and brush fires. Providing there is not toomuch wind, the foam remains in position and,besides the direct effect of stopping flames, thedrainage helps to create a wet surface to impedeany creeping fire. Application should be made notless than 5 minutes nor generally more than 60minutes before the fire front hits the barrier.

5.4 High Expan ion oam

(a) General

High expansion foam is produced from SYNDETsynthetic detergent concentrate. The finished foamhas an expan-sion ratio that can range from 200: 1to 2000: I although the high expansion foam gen­erating equipment used by the fire service normal­ly produces finished foam of expansion ratiosbetween 300: I and 1200: 1. High expansion foamcan be effective in extinguishing fires in a widerange of solid and liquid fuels.

From the same amount of foam solution, fire servicehigh expansion foam generating equipment can pro­duce, in terms of volume, in excess of 10 timesmore finished foam than medium expansion foam­making equipment and 100 times more finishedfoam than low expansion foam-making equipment.

The high expansion foam is very slow-flowing andis poured on to a fire rather than projected. It ismainly intended for use to totally 'flood' enclosedareas such as basements, warehouses, machineryspaces and ships' holds. It has also been used inhazardous areas where it can be unsafe to send per­sonnel, such as refrigerated rooms, mine shafts andcable tunnels. Due to the large volume of foamproduced from small amounts of foam solution,high expansion foam can also be used in instanceswhere there is a limited water supply and wherewater damage needs to be kept to a minimum.

High expansion foam can be very effective out­doors but only if the wind speed is very low.Outdoor uses include vapour suppression and, atlower expansions of the range, e.g. 300: J to 500: 1,in controlling fires in spiIJages of hydrocarbonfuels. Obviously. due to its density and the waythat it is produced, high expansion foam can onlybe applied very gently.

28 Fire Service Manual Firejighting Foam 29 r___________________________________________________...t.... .JI

Figure 5.4 A high expansion foam unit in operation.

(PhOlo: Mid and Wesl Wales Fil,' Brigade)

The major disadvantages of using high expansionfoam for firefighting are:

• the release of the water content of the foamis very slow and therefore this provides onlylimited cooling, particularly for deep seatedfires in combustible solids;

• the foam does not flow well, consequentlythe foam will be at its lowest depth at thefurthest point away from the generator;

• its poor flowing characteristics may alsolead to large air pockets in the foam wherecombustion can continue even after thecompartment has apparently been complete­ly filled,

• the heat resistance of the foam and its abili­ty to seal against hot surfaces is poor;

• due to large expansion ratios, high expan­sion foam is very light and can be blownaway by even a minor breeze and by the up­draughts caused by fires;

• the foam cannot be projected and so thefoam generating equipment must be posi­tioned very close to fires. However, in cer­tain situations, flexible ducting can be usedto transport the foam to the required appli­cation area.

• High expansion foam should not be used tofight fires involving chemicals which gener­ate enough oxygen to sustain their owncombustion, e.g. cellulose nitrate.

The slow release of water from the foam is benefi­cial when used for the vapour suppression of LPGand other similar liquefied gases.

Before the production of high expansion foambegins, as much information as possible must beobtained about any compartment that is about to beflooded, i.e. its nature, size, layout and contents. Ifthe contents of the compartment are stacked orplaced up to or near the ceiling, it must be realisedthat the foam blanket may not extinguish all of thefire, and preparations must be made to attack thislater. It must also be understood that the use ofhigh expansion foam will inhibit the use of any

other firefighting technique and may make it moredifficult to commit firefighters into the compart­ment at a later stage.

(b) Planning Resource Requirements

If the size of the compartment is known, it will bepossible to calculate approximately how muchfoam concentrate will be needed to adequately fillit. For compartments containing combustiblesolids, sufficient foam should be injected to ensurea depth of at least I metre above the highest fireaffected object. For flammable liquids, the fillheight should be considerably more than I metreabove the fuel surface.

To calculate the fill height, the approximate foamoutput of the particular high expansion foam gen­erator in use will need to be known in m3/min atthe required expansion ratio as will its consump­tion of foam concentrate in litres per minute.

A simple table kept with the generator would help,but allowances must be made for the initial fastbreakdown of foam that will occur due to the effectsof heat, flame and hot objects. Holes in the com­partment walls, and the need to regularly 'top-up'the foam for a ti me after control of the fire has beenachieved, will also need to be taken into account.

The minimum requirement should be to have suf­ficient high expansion foam generated to lift theheight of the foam in the compartment by at leastI metre per minute, with total filling of the com­partment to the required height taking no morethan 8 minutes. Resources should be made avail­able to 'top-up' the foam for at least a further 30minutes. In order to allow for the losses due to thebreakdown of the foam, at least a total of twice theamount of resources (i.e. foam concentrate andwater) required to fill the compartment to therequired height should be made available beforefilling commences. If high expansion foam is to beused outdoors, then further allowances will need tobe made for foam that is likely to be blown away.

(c) Positioning of High ExpansionFoam Generators

High expansion foam generators should always,where possible, be placed in the open air, as prod-

ucts of combustion of the fire could otherwiseaffect the volume output and stability of the foam.

Ducting can be used on the outlet of a generator toenable it to operate in fresh air while effectivelytransporting the foam to the required area. Thisducting should be kept as short as possible, with­out kinks, and any opening used must be larger incross-sectional area than the ducting, to cut downback-pressure and to ensure that the maximumpossible output can be generated. Doorways,hatches etc. may be usable as they are, but, in someincidents, openings may have to be made orimproved.

The further high expansion foam has to travelthrough ducting or other areas in order to reach thefire, the more breakdown of the foam that wi 11 takeplace. Ideally, the foam generator should be posi­tioned as near to the fire as it is as safe and practi­cal to do so. Tests have been carried out using lay­flat polythene ducting on the outlet of a highexpansion foam generator (Reference 5). Using an8 metre length of this ducting, the volume of thefoam produced by the generator fell by more than50%. However, even though this is a big reductionin the foam volume output, even less foam is like­ly to reach a fire affected area 8 metres away froma foam generator if ducting is not used.

There are various kinds of high expansion foamducting, but a heat-resisting type must obviouslybe used if the conditions demand it.

(d) Level of Injection

If HX foam can be injected at the floor level of thecompartment, it will not have to contend with heat­ed currents of air to penetrate the area. However,operational conditions nearly always require it tobe injected at a higher level, and this will workprovided that the injection is kept going steadily.There will probably be an initial fast breakdown ofthe finished foam but the sheer volume shouldsoon penetrate.

(e) Ventilation

If a large volume of foam is to penetrate a com­partment, it must displace the air in that compart­ment. Also, when the foam first attacks the fire, a

30 Fire Service Manua! Firefighting Foam 31

(f) Maintaining Foam Production

considerable amount of the water in it will flash tosteam. All this, together with the products of com­bustion, will result in a back-pressure which. if notventilated, will physically prevent the injection ofmore foam.

Changes in the colour of the smoke issuing from thefire will give a good indication of whether the foamis achieving control of the fire. As mentioned above.there will be a degree of breakdown of the foam,and the application of high expansion foam into thecompartment should not be stopped, without goodreason, until the fire is extinguished. Deep seated

33Firefightillg Foam

a high-pressure hose-reel branch;

a dry powder extinguisher;

a high expansion foam generator in suctionmode. using semi-rigid ducting.

•••

The removal of HX foam from a compartment isnot easy. Tests have been carried out using variousmethods (Reference 6) and, of these, the followinggave the best performance:

(i) Clearing/Collapsing the Foam

All of these methods have disadvantages, and theoperational situation will largely determine whichmethod is used. A high-pressure hosereel is effi­cient but will cause further water damage. A drypowder extinguisher is also extremely efficient butleaves a combined powder/water residue whichwill have to be cleaned by a salvage team. A highexpansion foam generator works well, providedthat the water residue is led away by hose and theducting is not too long but, to clear all of a com­partment, the ducting will have to be movedaround like a vacuum cleaner. This will be difficultwhere the compartment is large or where there ismachinery, stacked goods, racks etc.

One obvious point which firefighters shouldremember is that the longer the high expansionfoam is left, the easier it is to break down.Drainage from the foam weakens the bubble wallsand, in the tests using breakdown by water, it tookless water to complete the job after a 30-minutewaiting interval than after a 15-minute interval.

the compartment may contain trapped gaseswhich, with the introduction of fresh oxy­gen, could result in backdraught conditions;

open,ings, machinery, electric cables etc. willall be harder to discern, and progress musttherefore be even more careful than usual.Guide lines and communications equipmentshould always be fully used if firefightersneed to be totally immersed in HX foam.

High expansion foam, even in a relatively well­known environment, has a very claustrophobiceffect. In an unknown compartment this effect canbe heightened. Other hazards encountered are:

(g) Entering the Compartment

fires in some materials may require the maintenanceof a foam blanket for a considerable length of timebefore being completely extinguished.

All personnel entering a high expansion foamfilled compartment should wear BA, and theBA procedures should be rigorously applied.Firefighters should take in a hosereel or 45 mmhose line ready to extinguish with water any smallpockets of fire still remaining, taking care that firedoes not break out behind them.

(h) Hazards in High Expansion Foam ­Safety of Personnel

• penetration of light from torches and equip­ment is severely affected;

• there is a general loss in effectiveness ofvision, hearing and sense of direction, i.e.disorientation;

• audibility of speech, evacuation signals,low-pressure warning whistles and distresssignal units is also severely restricted;

• transmission of heat is reduced and the loca­tion and travel of fire are therefore harder todetermine. Thermal image cameras are alsoineffective. Damage to structural featuresabove and around may not be visible, withthe danger of ceilings etc. collapsing ontofirefighters;

•

•

Fire Service Manual

One of the factors that shouldbe assessed is where thecompartment can be safelyventilated. Due regard should begiven to the risks of Ilashoverand backdraught when ventinga fire (see Fire Service lVlanualVolume 2 - COmlJartment Firesand Tactical Ventilation).

Should conditions be safe to do so, the best placefor a vent is diametrically opposite the genera­tor(s), at the highest level. To be most effective,Jow-Ievel openings may need to be blocked andsuitable openings may need to be made at a highlevel in order to ensure that the compartment isfilled with HX foam as quickly as possible.Opening up a ceiling or roof would be ideal, but insome cases the highest available opening may beseveral feet below the top of the compartment. Tofacilitate ventilation, smoke extractors could beemployed in the openings; high expansion foamgenerators can be adapted for this purpose. Theofficer-in-charge must station crews with hand­controlled branches or hose-reels at all the ventila­tion openings to cover any fire which might appearthere. Under no circumstances should any of thiswater be injected into the compartment, however,as this would break down the foam.

32

irefighting Foam

Chapter 6 - Practical Scenarios

hap

6.1 General

In order to discuss the use of firefighting foams itis necessary to consider practical examples.

In this Section, information is given on how typicalfires may develop in a variety of practical situations,and how the fire service could respond using vari­ous firefighting foams, equipment and techniques.

In practice, no two fires are exactly the same andso any generalised description is bound to be asimplification. The descriptions that follow eachstart with a summary of some of the difficultiesinvolved with each type of fire. The second part ofthe scenario is a brief description of a typical fireand how it might be fought, particularly by the useof firefighting foam.

No allowance has been made in these scenarios forback-up or reserve capacity in the event of the firstresponse not succeeding. Also, no direct referenceis made to the number of firefighters required. Thenumber of appliances which attend will generallydetermine the personn'el available. The numbers ofappliances mentioned are those needed for directfire attack. If additional personnel are required,further appliances would be in attendance, butthese would not form part of the equipment needsfor the fire attack.

Identifying typical scenarios is a first step in pre­planning for a fire attack. The main difference isthat the fire preplan is concerned with moredetailed logistics and provides a sufficiently highlevel of response to cope with unforeseen difficul­ties and developments.

Before discussing the scenarios In more detailthere are several general points on preplanningwhich should be mentioned.

6.2 Preplanning

For smaller scale incidents, much preplanning hasbeen performed by the UK fire service over manyyears. The results of this work underpin the FireService Manuals, the basic and more advancedtraining courses and the selection of equipmentthat is carried on brigade appliances.

Formalised preplanning is usually carried out forlarger incidents where the following factors needto be fully considered and arrangements put inplace before the event occurs:

• risk assessment;

• supply lines of material/equipment;

• fresh resources of personnel;

• clear decision making on the fire ground;

• communications with third parties.

It can be very useful to use formalised preplanningfor medium and small scale incidents, both as atraining aid for firefighters and as a means of high­lighting any deficiencies in existing methods,equipment and information.

6.3 cenarios

The fire scenarios below set out the conditionswhich could exist for a particular type of fire inci­dent, and indicate how it could be assumed to devel­op. The effectiveness of the fire service response isdiscussed, pm1icularJy in relation to the foam­making materials, equipment and tactics required.

These scenarios are idealised cases and it isappreciated that the timing. aims and problems

Firejighting Foam 35

(a) Road Tanker Crashes

A "worst case" would be to assume that all of thecontents of a road tanker are spilt, say a total of 38

associated with each real fire incident will varyconsiderably. The use of these scenarios is toindicate the likely quantities of foam, water andequipment needed for direct fire attack.

37Firefightin[!, Foam

Supply of backup foam stocks and rapid access tofurther water supplies would need to be providedurgently since, in a multiple pile-up, secondaryspills and fire are probable. The water supply prob­lem is eased by the availability of hydrants onsome motorways.

(ii) Rural Tanker Crash

A rural tanker crash is likely to lead to a less exten­sive spill. Roads are narrower, more cambered andoften flanked by banks or ditches. In these casesthe brigade is more likely to be called upon to tack­le a number of smaller isolated fires in accumula­tions of liquid, particularly since with longerresponse times shallow spills will have beenburned off. There would be some justification forless than 25% of the calculated foam supply figure,although water supplies are likely to be a major

To illustrate some of the factors that could be takeninto account, the following three cases, involvingtanker crashes, are considered.

(i) Motorway Tanker Crash

A tanker crash on a motorway may involve highspeeds, high impact energy and therefore a rapidliquid discharge over a relatively flat surface. It isnormal practice in some brigades to dispatch a firstresponse team of four appliances to such incidents.The main objective in fighting fires following amotorway tanker crash is to control and extinguishfire around exposed vehicles prior to attemptingthe rescue of trapped or stranded motorists. Forsuch incidents, there are arguments for more thanthe 25% foam provision discussed above, howev­er, the emphasis should be on very rapid deploy­ment of the first attack.

Figure 6. J A rural road incident.(Photo: Wan\'ickshire Fire llnd Rescue Sen';cej

In taking a more practical view, there are manyother factors that could be taken into considera­tion. Road surfaces are rarely flat. The road cam­ber will tend to direct spillage into a more restrict­ed area. Kerbs, banks and surface irregularitieswill tend to limit the spread of liquid, whilst rain­water drains will carry some away (with possibleserious consequences of sewer fires and explo­sions). In addition. tankers are generally compart­mentalised and it would be highly unusual,although not unknown, for all of the compartmentsto be breached.

From a practical viewpoint, it would be difficult todeploy this amount of equipment rapidly. Even ifhydrants were available, the time for laying hosewould be considerable. In addition, assuming afuel burning rate of around 4mm per minute, thefire would have burnt itself out in just over 7 min­utes if no firefighting took place.

In terms of equipment, this would require theequivalent of fourteen 450 lpm foam-makingbranches and inductors, and approximately fourpumping appliances to supply the branches.

cubic metres, and they spread rapidly over a flatsurface. Then a total area of 1520 square metrescould be covered to a depth of 25mm (a spill, seeChapter 3, Section 3b).

Using the Home Office recommended minimumfoam application rate for film-forming foams of 4Ipm/m2 for fifteen minutes duration, a total of91,200 litres of foam solution would be needed ata foam solution flow rate of 6080 litres per minute.This would require 2,736 litres of 3% film-form­ing foam concentrate and more than 88,000 litresof water.

Perhaps, because of these factors the foam require­ment for first response could be reduced to 25% ofthe "worst case" i.e. 684 litres of 3% film-formingfoam concentrate, 22.116 litres of water and a foamsolution f10wrate of 1520 litres per minute. Thiswould require four 450 litre per minute foam-mak­ing branches and one pumping appliance. However.experience and likely local conditions would needto be taken fully into account in setting such guid­ance for the first response capability, second andsubsequent responses and back up resources.

Fire Service Manual

A wide variety of flammable liquids and toxicchemicals is transported by road throughout theUK on urban and rural roads and motorways.Lorries can typically carry 38m' of flammable liq­uid cargo. A number of incidents have occurredwhere the contents of road tankers have been dis­charged onto the road and the resulting fire hascaused loss of life.

In practice, greater resources are often committedbecause of the uncertainty of how serious the inci­dent may become, to provide a ready reserve capac­ity and to provide indirect support or relief to themain fire attack team. It is left to each individualbrigade to interpret how the objectives would beachieved given their own mix of equipment, materi­als, philosophy, logistics, and personnel policies.

When a road tanker is damaged in an accident it isunlikely to discharge all its contents at once ontothe roadway. More usually, liquid will steadilyleak from breaks in the tank pipe-work or in thevessel itself. Frequently, not all the contents aredischarged, and a substantial volume may remaininside the vessel. Spillage of flammable liquidmay catch fire immediately or there can be a delaywhile the flammable vapour spreads far enough tocontact a source of ignition.

Consequently, there are a wide variety of fires thatmay face firefighters when they attend a roadtanker crash. These can range from an extendedspill fire, to a spreading fire, a running fire, a tankfire, or a combination of them all.

In order to make an estimate of the foam resourcesthat should be available on fire appliances, a num­ber of factors will need to be evaluated. but initial­ly it is important to set the upper limit of whatmight be required by establishing a possible"worst case".

36

Figure 6. J An urban tanker incident.

(Photo: Surrey Fire and Rescue Service)

problem, and additional water carrying capacitymay be considered necessary.

(Hi) Urban Tanker Crash

An urban location for a tanker crash involves a fur­ther set of considerations. Water will be readilyavailable, brigade response time rapid and flam­mable liquid leakage rates generally lower becauseof reduced impact speeds. However, there is asevere risk of secondary fires being started whichmay become life threatening. Whilst there arefewer physical factors calling for a large foamattack, the exposure of human life can be severeand there may be more need than in rural areas foruse of conventional water branches to extinguishsecondary fi res.

There should be far less difficulty in an urban areain obtaining a strong and rapid backup response

which will have sufficient resources to meet thedemand. Other complications which need to beconsidered in preplanning are:

• local evacuation from the area could beaffected by a vapour cloud accumulation;

• traffic control;

• notifying of water authority and local mediaof explosion potential in sewers;

• flushing and venting of sewers;

• LEL (Lower Explosive Limit) measure­ment.

If the foam supplied with the first response is notbest suited to the flammable liquid involved thenreserve stocks of a more compatible foam could be

called up. In the meantime it is common practice totackle the fire with whatever foam is available, andthis must obviously continue to be brigade policyas it could take a considerable time for the alterna­tive foam to arrive.

(b) Rail Tanker Crash

As with road transport, many flammable liquidsand toxic chemicals are transported by rail throughurban and rural areas of the country. There are twotypes of rail tanker car generally used. A two axlecar of approximately 45m3 (45,000 litres) capacity,and a bogie car of approximately 100m3 (100,000litre) capacity. Diesel locomotives can haul up to1,500 tonnes, and trains of two axle cars couldcomprise of as many as 22 cars.

The potential exists for a major incident arisingfrom a rail crash. A wide range of risks areinvolved which require a variety of equipment andflexibility of approach from the fire service.

It' LPG or sinlilar liquefied gasesare being transported there is arisk of a BLEVE. Depending onthe result of an operational riskassessment ~lt such an incident,it may be conside.·ed that apolicy of evacuation of a widearea may be the only safecourse of action.

Even with ordinary flammable and combustibleliquids, exposed tanks can rupture suddenly andviolently. If a passenger train is involved, there isthe possibility of a major rescue operation in par­allel with firefighting activities.

The speeds at which trains travel and their largemomentum means that when a crash occurs, strongforces can be brought to bear on the tankers, giv­ing a high chance of major damage to the structureand rapid discharge of the contents. In urban areasthe potential life exposure can be high and there is

a possibility of multiple secondary class A fires,particularly where the rai I track is elevated abovesurrounding property or where buildings lookdown upon the track. In rural areas there can besevere problems of access and it may require timeto lay on adequate water supplies.

In the case of a single rail tanker car spilling itscontents rapidly over a flat surface, the aJea whichcould be covered to a spill depth of 2Smm is4,000m2 for a 100m3 tanker and l800m2 for a45m3 tanker. Using the Home Office minimumrecommended application rates (see Chapter 4) of4 Ipm/m2 for film-forming foam concentrates overthe minimum application time for a spill fire of 15minutes gives a foam solution demand of 16,000lpm for the larger tanker and 7,200 lpm for thesmaller.

For the larger tanker, this would require totalresources of 240,000 litres of foam solution, con­sisting of 7,200 litres of 3% film-forming foamconcentrate and 232,800 litres of water, ninepumping appliances and thirty six 450 Ipm branch­es or nine 1,800 Ipm monitors.

For the smaller tanker the equivalent requirementswould be 108,000 litres of foam solution consist­ing of 3,240 litres of 3% foam concentrate and104,760 litres of water, four appliances, and 16branches or four monitors.

From a practical viewpoint, assuming a fuel burn­ing rate of around 4mm per minute, the fire wouldburn itself out in just over 7 minutes if no fire­fighting took place. However, the surface around arail crash is likely to be very uneven leading to aselies of pool fires which will last longer than aspill fire but may require the same amount of foamdelivery equipment because of their physical sepa­ration.

If it is assumed that because of the unevenness ofthe surface of the ground, the area of the burningliquid is reduced to a quarter of that for a spill, andthat a foam application duration of 30 minuteswould be required because of the deeper accumu­lations of liquid, then a practical estimate of firstresponse capability is 50% of the figures calculat­ed above.

Firefighting Foam38 Fire Service Manual 39 ~

----------- ........b .;..__------ .....Jlj

Figure 6.3

Rail incidenl in\'olving

petroleum tanker

trucks.

(PhOlo: f-!umbel'.\u!e Fire

Brig(lde)

Figure 6.4

Aircraft crash on

approach to airport.(Photo: Wllnnchhht, Firfl and

Rescue Sernc(')

There are many chances of complications with arail tanker crash, and caution would lead most firebrigades to mobilise a considerably larger firstresponse and rapidly arrange for support to be pro­vided.

Tactics for such an incident require considerableflexibility. Water supplies may be restricted in theearly stages. and the best use of limited quantitiesof water is to lay a foam blanket beneath exposedvehicles. FP or an alcohol resistant foam would bepreferable because of their good heat resistanceand stability. Water will be required for class Afires either in the surrounding area or in the interi­or of passenger coaches. Water monitors may alsobe needed for cooling exposed tanks, particularlyif they are exposed to a flare fire. A further tankrupture must be expected and tactics set out withrapid redeployment or retreat in mind. Care wouldneed to be exercised to ensure that any foam blan­ket in the area is not broken down and that liquidfuel. especially if already burning, is not spreadover a wider area'by the application of water.

In major incidents, such as a rail tanker crash, theavailability of personnel may be a more criticalfactor than equipment. Firefighters are needed forhose laying to water sources, rescue, relief, evacu-

ation, maintalDlng supplies of foam concentrateand repositioning equipment. For such incidents itis common to mobilise more appliances thanrequired for operational use to ensure adequatenumbers of personnel are available.

(c) Aircraft Crash

Generally at aircraft incidents on airports or airfieldsthe Local Authority Fire Brigade augment the airportfire service. The attendance time for the airport fireservice to any incident that occurs anywhere on theirairfield is normally less than two minutes althoughregulations state it must be less than 3 minutes. Theairport fire service will have emergency plans formost eventualities and it is likely that they will havebeen put into action well before the arrival of theLocal Authority Fire Brigade.

In addition, the airport fire service must attendincidents up to 1000 metres from the runwaythreshold but, for incidents further afield, they mayattend in a reduced capacity, depending on the dis­tance from the airport.

In an off-airport crash incident. a situation couldarise where say a Boeing 747 crashes, after take­off, several miles from an airport. Such an aircraft

could be virtually fully laden with Jet Al (aviationkerosene) which amounts to about 136m3 (136,000litres).

If ignition takes place, it is possible that much ofthe spill would have burned or drained away with­in 10 to 20 minutes of the incident and probably bythe time the first Local Authority Fire Brigadeappliances arrived at the scene of the incident. Theinitial crash/rescue teams to arrive might have tocontrol and extinguish a large number of wide­spread class A fires and class B pool fires whilstassisting any survivors from the incident or frominvolved buildings, vehicles etc. In addition, flam­mable vapours would be given off from anyunburnt fuel for several hours after the incidentand this, too, would need to be dealt with.Problems of adequate water supply and access arelikely to hamper any large scale firefighting exer­cise and therefore it is unlikely that large amountsof foam concentrate would be required.

Not all aircraft crashes will result in fire. Therehave been occasions where aircraft have crashlanded at low speed and from low altitude. [n suchsituations. the aircraft may have broken into sever­al large parts without bursting into flames. It ispossible that there could be many survivors.

In these circumstances, there is a risk of fire fromfree fuel flowing out of broken fuel tanks and fuellines. This fuel should be immediately coveredwith a thick layer offoam. Frequent replenishmentof the foam blanket would be required in order toensure continued protection. At all times, foamapplication should be as gentle as possible in orderto minimise fuel contamination of the foam. Evenwhen a suitable foam blanket has been applied,sufficient firefighting equipment should bedeployed. with firefighters in constant attendance,in case a fire breaks out within or around the foamblanket (see Chapter 5, Section 2(a) (viii)).

Should a large fire break out, then a mass applica­tion of foam would be required in order to sup­press the fire. Given the limited resources likely tobe available, the main objective of the attackshould be to keep the fire away from any survivorsand rescue personnel without obstructing theirescape route.

Foam branches should be positioned as closely aspossible to the fuselage, the initial discharge beingdirected so that the foam drives the fire outwardsand away from the wreckage. If possible, fireshould be kept at least l5 metres away from anintact fuselage.

40 Fire Sen'ice Manual Fireflghting Foam 41

(i) Engine Room

(d) Marine Fires

Great caution should be used when applying foamnear to wreckage as there is a risk of flushing fuelunder or into the fuselage where it can present afar more serious hazard. Similar care should betaken to avoid the possibility of a water jet dis­turbing any foam blanket already laid on a liquidfuel surface.

43Firefighting Foam

Deck fires are more likely to be intense duringpumped loading and unloading operations, inwhich case back-up support should be availablefrom the adjacent jetty. However, various cleaningand transfer activities take place at sea and maygive rise to a running/spill oil fire.

Low expansion foam, either a salt water compati­ble film-forming or FP foam would be suitable atthe Home Office recommended minimum applica­tion rates and minimum application times for spillfires. However, in reality, conditions at sea arelikely to result in higher application rates, applica­tion times and hence greater quantities of foamconcentrate being required.

called, this is probably as a result of the equipmentbeing out of service or of it being inadequate forthe purpose.

Under normal conditions, water is available directfrom the ships hydrant system although boosterpumps may be necessary in some cases.

The firefighters arriving on the scene mustquickly assess the area of deck that could beaffected by the spill and appropriate quantitiesof foam concentrate and branches should berequested. If the fire is large and spillage offlowing oil extends into the sea, assistancefrom firefighting tugs may be required.Communications and co-ordination should bemaintained between the fire service, coast guardand the ship's master.

If possible, attempts should be made to shut off theflow of oil to the spill. Water fog sprays and lowexpansion foam streams may be necessary toensure firefighters are protected whilst they reachthe necessary isolating valves.

In addition, it may be necessary to close hatchesand ventilation louvers to prevent burning oil fromentering further into the ship.

Once sufficient foam stocks and branches havearrived, a concentrated low expansion foam attackcan be mounted from a safe distance gradually lay­ing foam onto the edge of the spill, working backto the source of the fire.

• this is equivalent to 7 x 20 litre drums of 3%foam concentrate.

• at 3% concentration, 4,500 x 3% = 135 litresof 3% foam concentrate is required;

• Assuming the use of 450 Ipm MX foam­making branches, with an output of 19.5m3

of finished foam per minute;

• 200m3 would require one branch for approx­imately 10 minutes or two branches forapproximately 5 minutes;

foam, the material and equipment and foamrequirements would be:

• 200m3 of medium expansion foam;

• the foam solution requirement for twobranches is 2 x 450 Ipm x 5 minutes =4,500;

More foam concentrate and foam solution thanthat calculated above would be required to allowfor foam burn off and for continued application.The extra allowance for foam burn off is substan­tial but varies with the length of pre-burn and themass of steel exposed.

(H) Deck Fire

Estimates of up to three times the initial calculatedapplication quantity could be used to allow forburn off and a further three times the initial esti­mate for continued application after fire extin­guishment. However, in an area where the struc­ture has a high thermal capacity, such as an engineroom, even this may not be enough. Allowing forfoam burn off and continued application in such asituation could result in as much as 10 times theamount of foam concentrate calculated abovebeing required. That is 1,350 litres of 3% foamconcentrate, the equivalent of 68 drums.

In the case of a similar sized coastal tanker, thisexample considers a deck fire originating from anoil leak in the deck pipe work system. Tankers nor­mally carry their own on board foam systems tocover the deck area. These are normally operatedby the crew, however, if the fire service have been

If low expansion foam does not reduce the level ofthe fire sufficiently to gain entry, or if access is dif­ficult, it may be necessary to use medium or highexpansion foam to control the fire and to cool heat­ed steel plates to prevent damage to hoses and toprevent reignition. In addition, cooling may berequired to prevent heat transmission starting firesin the cargo or other areas of the ship. Foam induc­tion must take place at deck level and, if the fire ison the lower decks of a large ship, it may be nec­essary to reduce pumping pressure.

To achieve safe entry into a ship and perform a firesearch is a challenging and hazardous operationeven for skilled firefighters. In addition to theusual problems of using breathing apparatus indark confined spaces, layers of hot gas may beencountered beneath deck levels, or thermal up­drafts from shafts. Progress is inevitably slow andthe steel work is likely to be very hot in places.Reserve crews will probably be required and pro­tracted working should be expected.

In the first instance, attempts should be made toisolate the flow of oil to the fire. It may be neces­sary to lay a blanket of sea water compatible lowexpansion alcohol resistant film-forming or fluo­roprotein foam to help to protect firefighters fromdeck level fires and provide water fog sprays tocool and protect as they enter enclosed spaces.Any means of venting the enclosed space bymeans of ducts, Iou vel'S, dampers or hatchesshould be carried out with the assistance of theships chief engineer.

Assuming a lOm x 10m engine compartment is tobe filled with a 2m depth of medium expansion

The logistics of mounting a medium expansionfoam attack involve considerable quantities offoam concentrate and there may be difficultiesin providing this if the ship is at sea in roughweather.

When discharged into an area with many hot metalsurfaces, the initial foam application will be large­ly destroyed. The resulting cooling effect is useful,but steam generation can be a further hazard tofirefighters. For this reason, the foam requirementscalculated in the following example are probablyfar lower than those needed in practice

Fire Service Manual

The UK fire service is not responsible for combat­ing fires offshore in UK territorial waters.However, any fire brigade with coastal boundariesmay exercise its power under the Fire Services Act1947 (as amended by the Merchant Shipping andMaritime Security Act 1997, Section 3), to attendfires at sea outside its areas particularly wherehuman life was endangered. The following Sectionlooks at three examples of maline fires where fire­fighting foams may be used.

In addition, there may be areas where firefightingfoam will not penetrate and so other suitableextinguishants such as CO2 and dry powdershould be made available. The use of these back­up agents should be confined to spreading andrunning liquid fuel fires, the inhibition ofenclosed spaces such as wing voids, or to dealwith special fires such as in engine nacelles orundercarriage assemblies.

The example chosen is from a 2,000 tonne coastaltanker, although it is quite possible that firebrigades could be called to attend fires in any sizeof vessel from a yacht up to a ultra large crude car­rier (ULCq of 400,000 tonnes or more. The prin­ciples of operation are similar for all steel con­struction vessels, but the complexity of the entryroute, access to the engine room and size of theroom itself would vary considerably.

42

A fire could occur from an oil fuel pipe breakagein the machinery space, with oil leaking onto theengine room deck and being ignited as a result ofcontact with hot metal surfaces. If the on boardsuppression systems (e.g. CO2 or inert gas sys­tems) and first aid fireflghting fail to extinguishthe fire, then the fire service will be asked toattend.

b

Additional water hoses may be required to cool hotsteel surfaces to prevent re-ignition and possiblespread of fire to the stored cargo. However, careshould be taken to ensure that foam blankets arenot broken down and that liquid fuels, and liquidfuel fires, are not spread by cooling water.

tanks after extinguishment of the fire on the liquidsUlface. Unless extinguished or dislodged, thesedeposits can fall back into the cargo and causereignition hours after the first extinguishment.

(e) Terminals - Jetties

• Foam monitors positioned at such an eleva­tion that the jetty deck and the ship's deckare covered at all elevations. The foam mon­itors should be adjustable and may be fittedwith either hydraulic or electronic remotecontrols.

buildings, it is possible that damage to the sup­porting structure and fire spread to the remainderof the building could occur. In a high risebuilding, fire spread, structural damage or smokelogging could have particularly serious conse­quences.

(iii) Cargo Tank Fires

If a cargo tank fire has developed after a collisionwith a similar coastal tanker carrying fuel oil andthe assistance of the local fire services has beenrequested by the ship's master, the firefightersmust initially assess the requirements for foamconcentrate, branches and equipment.

Where burning oil is spilling from a ruptured tankinto the sea, it may be necessary for the firefight­ers to call for the assistance of fire fighting tugs.The quantities of foam concentrate requireddepend on the area of the cargo tank and hereadvice is required from the ship's master. Furtherquantities of foam concentrate would also berequired for the spill fire. Low expansion foam,either a sea water compatible film-forming or FPfoam, would be suitable at the Home Office rec­ommended minimum application rates and mini­mum application times for spill fires or for tankfires (see Chapter 4), dependi ng on the depth offuel and the size of the cargo tanks. In estimatingthe quantity of foam needed in the cargo tank,further allowance should be made for burn offand re-application. This may involve up to fourtimes the calculated amount of foam for each ofburn off and re-application.

Once sufficient stocks of foam and branches havearrived, the foam attack should be concentrated ata safe distance from the windward side on eachtank until the fire is controlled. If the up-draughtfrom the seat of the fire is too high for the foamstreams to penetrate, other entrances should befound to apply the foam blanket.

When the tank fire has been extinguished, thefoam application should be continued until the sur­rounding steel plates are sufficiently cool so as notto reignite the remaining oil.

Glowing char embers often remain adhering to theupper walls and roof on the inside of oil cargo

The UK fire service is responsible for controllingand extinguishing fires on oil and gas terminal jet­ties. Where jetties are sited in remote areas, firebrigade response times may be high. On arrival,firefighters will often be faced with restrictedaccess and the need to carry equipment along jet­ties to reach the remote loading sections. In morepopulous river estuary sites, there is the potentialfor exposure to the surrounding community, par­ticularly from burning oiJ slicks on the water orburning vessels drifting from their moorings.

AI I of these factors make the provision of adequatefixed fire protection facilities on jetties a high pri­ority.

The majority of jetries should be equipped with thefollowing:

• Fire pumps providing fresh or sea water tothe jetty hydrants and monitors.

• Multi outlet hydrants with hose connectionsalong the jetty approach way.

• Hose, branches, monitors, inductors andfoam concentrate.

• Water monitors, adjustable or remotelyoperated, which are fitred with jet/fog noz­zles. These may be arranged to provide awater curtain between the jetty and the ship,or for cooling the ship loading manifold areaor the jetty head area.

• Multi outlet hydrants along the jetty deck,together with adapters for internationalshore-ship connections.

• Open water spray nozzles installed at theship side of the loading facility at variouselevations.

• There should also be space at the jettyapproach for firefighting appliances andbulk foam vehicles.

If a fire occurs at a loading station on an oil termi­nal, the fixed equipment should be operated tomaximum effect. This is to ensure that personnelcan be evacuated quickly and safely and that thejetty is protected from exposure to the fire.

With this degree of fixed protection, the need forintervention by the fire service with large amounts ofequipment is greatly reduced. A tirst attendance oftwo fire appliances should be able to supplement thefixed systems in the event of minor sections failingto function. However, the equipment handling prob­lems may require considerable resources of person­nel and the response should take this into account.The considerable potential for serious loss shouldmean that a strong second response backed up byfirefighting tugs is provided. In the event of vesselimpact on the jetty it may be necessary to isolate sec­tions of the fixed tire protection system so that theundamaged portion near to the shore can remain inoperation.

Isolated sections of jetty may well be dealt with byfire boats.

(t) Boiler Rooms

Oil-fired boiler rooms in commercial and industri­al properties are a specific example of where firebrigades use firefighting foams on a routine basis.Most boilers in the UK are equipped with auto­matic shut-off valves on the fuel supply line at thepoint of entry to the boiler house. When the firebrigade alTives at the scene of a boiler room fire, itis often difficult or dangerous to gain access anddetermine the extent of the potential fire.

The risk exists of an oil tank rupture leading to amajor fire and possibly a boiler explosion. Sinceboiler houses are usually at the lower levels of

External foam inlets are usually used to deliverlow or medium expansion foam into the room andventilation panels should be removed to clearsmoke logging. At this stage it may be possible toenter the boiler room and isolate the source of anyfuel leak.

When used in conjunction with a single hose inlet,one 450 Ipm MX branch would produce approxi­mately l5m3/min of finished foam (this figureallows for a reduction in the expansion of the foamdue to the restricting effect of the foam inlet).

For a boiler room fire, a 2m foam blanket shouldbe produced. To achieve this in a boiler room offloor area 100m2 would require the following foamresources:

• Total amount of finished foam required

=Height of room x floor area=2m x 100m2

=200m3

• Total foam application time

=Total amount of finished foamBranch output per minute

=200m3

15m3/min

=13 minutes 20 seconds

• Total amount of foam solution required

= Branch flow x Total foam applicationtime

= 450 lpm x J3 minutes 20 seconds

=6,000 litres

44 Fire Service Manual Firefighting Foam 45

----------------- .2rn ~J

(g) Warehouses

The potential advantages of using medium expan­sion foam in such situations are:

No allowance has been made in the above figuresfor burn off or for any necessary re-application.

Possible movement of the gas cloud shouldbe anticipated and the area of the probablepath evacuated and sources of ignition elim­inated.

Dense curtains of water can be used to directthe gas cloud away from ignition sourcesthat cannot be eliminated. Monitors, fansprays and branches set in fixed positionswill enable firefighters to retreat frompotentially dangerous situations where theymight be exposed to the gas cloud.

Once the gas cloud has dispersed to theextent that its concentration is below thelower explosive limit (LEL) a search shouldbe made of any low lying areas to disperseother possible pockets of accumulated gas.

•

•

•

This example illustrates the use of firefightingfoams in vapour suppression. In the event of acollision between an LPG road tanker and otherroad vehicles, damage to the tank could result indischarge of the contents onto the road. When thefire services are alerted to this type of situation, theseriousness of an LPG spill is recognised and aseries of emergency planning procedures are set inmotion.

• up to 3 times the theoretical quantity may beneeded for re-application and for burn off inwarehouse fires.

(h) Vapour Suppression

• there has been no research into determiningsuitable application rates;

Several appliances are sent to the scene of the inci­dent and their approach is made from up-wind ofthe crash. After the leak is isolated, it is estimatedthat the spill could extend to about 2,000m2 and itis calculated that 4 high expansion foam generatorseach producing 133m3/min of finished foam at 7bar from 225 Ipm of foam solution, could cover thespi 11, with an average blanket thickness of around 2metres, in approximately 8 minutes. This wouldrequire approximately 108 litres of SYNDET foamconcentrate when used at 1.5% concentration.

=Total foam solution x Foam concentration100

Total amount of 3% foam concentraterequired

=Total foam solution- Total foam concentrate

=6,000 litres- 180 litres

=180 litres

Total amount of water required

= 6,000 litres x L100

=5,820 litres

Medium expansion foam can be effective in com­bating low-level storage warehouse fires, particu­larly where a mixture of storage is involved pro­ducing a class A fire with possible involvement ofclass B liquid fuels.

•

•

• visibility can be retained - unlike whenusing high expansion foam;

• it provides greater volumes of extinguishingagent than low expansion foam and possiblyrepresents a better use of resources.

The main disadvantages are:

The above calculations represent the absolute min­imum application that could be expected for suchan incident. No allowances have been made for re­application during a prolonged incident or forreplacing foam blown away from the spill by wind.Due to the poor tlow characteristics of high expan­sion foam, problems may also be experienced incovering areas of the spill furthest away from thefoam generators.

Simultaneously to blanketing the spill with highexpansion foam, vapour dispersion/control mea­sures should be taken as follows:

•

••

the foam cannot be projected as easily aslow expansion foam giving problems indelivery to the seat of the fire, especially inlarge warehouses;

it is unsuited to fires involving materialsstored above 2m high;

it may not be effective on deep seated fires;

• The vapour cloud already formed would bevisible as a white fog due to condensed mois­ture. However, this is not necessarily the limitof the gas cloud. To effectively monitor thecloud location, explosiometers are required.

46 Fi" Smicc Manool Fi,,(igh'ing Foam 47 ~

..... ~>... -..JJII

Firefighting Foam Chapter

performance limitation of eXlstlOg equip­ment, particularly the maximum range andheight of monitor foam treams.

Figure 7.3 Fire extillguished. Foaming contillued to ensuresecurity offoall1 blallket. {Pilow: E.I.\·ex Fire (llId Rescue Sen'ice)

Figure 7. f Tank well alight. Paint scorched 011 adjacentlank. (Phmo: E.,·sex Fire ollll Re.H:uCf Sel"l'icej

Figure 7.2 Fire subsiding. Cooling ill progress.(Pltow: Esst'\ Fire and Rescue 5<,11';("("

•

vehicular access, movement and parking;

suitable locations for the deployment ofdelivery equipment;

inadequate water supplies;

Chapter 7 - Storage Tank Fires

By far the most common problems with refineriesand storage tank farms are as follows:

Whilst the fire scenarios are primarily concernedwith the tactics, equipment and materials neededto tackle storage tank fires. there would also be aneed for personnel to conduct support operations.This would be provided by firefighters whoseappliances would not be directly involved in thefire attack. The support operations are not consid­ered in' these scenarios.

• space for hose distribution;

7.1 Introduction

7.2 Common Problems WithRefinerie and torage TankFarms

Areas covered include fire development, the par­ticular problems that can be posed by these fires,the facilities available at refinery and storage tankfarms. the logistical problems that can occur due tothe large amount of conventional equipment andsupplies needed to fight these fires and the fire­fighting tactics that could be used. These aspectsare illustrated in several fire scenarios. As with thescenarios described in Chapter 6, these are ide­alised cases and it is appreciated that the timing,aims and problems associated with real fires willvary considerably from incident to incident.

In this Chapter. the use of con ventional fire serviceequipment to tackle storage tank fires is discussed.

••

•

Firejiglzting Foam 49

•

Access to and around storage tank bunds is oftenby means of a 3-4m wide road near to the outerbase of the bund wall and in many cases this mustmeet the simultaneous needs of monitor placementand operation, and appliance movement, parkingand operation.

Deployment of monitors should ideally be on, orbetter still outside, the bund wall. This is not alwayspossible as the walls may be too far from the tank.

The predetermined marshalling area for thepumps, foam supplies and foam induction equip­ment should be as close as possible to the fireground without putting either personnel or equip­ment at risk from the fire or potential spread of thefire. Every effort should be made to avoid com­mitting personnel and equipment inside the bundalthough this may sometimes be necessary (seethis Chapter, Section 5 (b) (x)).

One of the major difficulties created by the ofteninadequate number of hydrant outlets availableand the distance between them is the need for anexcessive number of hose lengths when using stan­dard firefighting equipment.

7.3 Tank Size

(a) General

Storage tanks for flammable and combustible liq­uids in excess of 91 m diameter and 27m high areused in the UK. Tanks in the range 45m to 91 mdiameter tend to be predominantly of the floatingroof design although some fixed roof tanks of over45m diameter do exist. The 27m high tanks are ofolder design and can generally be found in con­gested refineries and depots that are in traditionalindustrial areas such as along the North ThamesEstuary. Where space is available, tank heights canbe as low as 15m

(b) Tank Diameter

The effect of increased tank diameter on theseverity of storage tank fires is well recognised instandards. Standards for tank installations giveguidelines intended to show when fixed firefight­ing protection measures should be considered.These standards consider that tanks up to a limit

of around 9m diameter can have hand-held branchlines as a primary means of protection and tanksup to a limit of approximately 20m diameter canrely on portable foam monitors. If this equipmentis not available, or if tanks are greater than 20m indiameter, then fixed systems are recommended asthe primary means of fire protection.

In general, those who have had experience in fight­ing tank fires agree with the standards in that con­ventional equipment can be used successfully in"over-the-top" applications to tanks with diametersof up to 20m (an over-the-top application refers tofoam that has been projected over the sides of a stor­age tank and on to the surface of the fuel). In addi­tion, many experienced firefighters maintain thatconventional equipment can be used successfullyfor fighting fires in tanks of up to 45m in diameter;above 45m diameter, they believe that conventionalequipment cannot be successful. In addition, thelogistics of using conventional equipment for theselarger fires are said to be far too difficult. However,there are even significant problems involved intackling fires in tanks between 18m and 45m.

(c) Tank Height

The height of storage tanks can pose severe prob­lems when using conventional equipment. Manyfoam monitors are unable to project foam overtank walls in normal circumstances. In addition,when the distance of the bund wall from the tanksides is taken into account, often in the order of 50metres, the limited throw of conventional foamequipment can pose even more problems.

7.4 Fire Development

(a) Ignition

The first phase of any tank fire is ignition anddevelopment to the stage where the tank surface isfully involved in fire. Ignition can occur frommany different sources, for example, lightningstrikes, static electricity or burning embers fromflare stacks.

(b) Fire Plume

The fire plume from a fully involved tank fire canbe several hundreds of metres in height. The

rapidly rising flame and smoke can radiate heat tothe surroundings and draw fresh air in at the basecreating, in some cases, strong artificial winds atground level. In some circumstances, theseincoming winds can help to cool the area around aburning tank making working conditions morebearable.

Local wind conditions can incline the angle of thecolumn so that it closely approaches, or in somecases impinges directly upon, nearby structuresincluding other storage tanks. If the tank on fire ispartially empty, then the exposed ullage may beginto distort and collapse inwards towards the surfaceof the burning liquid. This process may happensuddenly, or may develop over a period of hours,leading to a situation where the wall of the tankcan be scrolled over and touching the surface ofthe burning liquid. This is a further complicationfor firefighters since the scrolled wall can shield alarge area of burning liquid from direct foamattack.

(c) Fuel

Crude oil, unrefined products and mixtures offlammable liquids, can be more difficult to extin­guish in storage tank fires compared with singleboiling point liquids. The presence of volatile"light ends" in these types of fuel tends to causedisruption to any foam blanket that has alreadybeen applied. If the foam blanket is not sufficient­ly deep, vapour can permeate the foam and igniteso greatly reducing its' resistance to heat andflames. Foams that "pick-up" fuel when applied(i.e. where the foam blanket mixes and becomescontaminated with fuel) can also cause a similarbreakdown of the foam blanket.

The Home Office recommended minimum appli­cation times (see Chapter 4) are longer for appli­cations to fuels that have a flash point below 40°C,this is a consequence of their increased volatility.

Flammable liquid tank fires will eventually burn toextinction although this is likely to take manyhours or even days. However, severe problems canOCcur during this time due to slop-overs and boil­overs (see this Chapter, Section 5 (b) (xiii)). Also,the cost of the product in the tank involved in thefire can make it desirable, from an owners point of

view, for the fire to be extinguished. In addition,further losses may occur if other nearby tanks aredamaged or even ignited by the radiant heat due tothe spacing between tanks being inadequate or dueto unfavourable wind conditions. The environmen­tal impact of a major storage tank fire is consider­able. Concerns of air pollution alone could buildup public pressure against a policy of "let it burn".

The liquid fuel contained within a tank will beconsumed at a bum rate which will vary accordingto the type of fuel and the conditions (e.g. windstrength, air temperature, surface area of fire) but arate of 4mm of liquid depth per minute is oftenquoted as an average for hydrocarbons such aspetrol. For crude oils, burning rates have been esti­mated to be as low as 0.2 mm per minute and ashigh as 15mm per minute depending on the type ofcrude.

In the case of single boiling point liquids, the sur­face temperature of the liquid will never rise abovethe boiling point of the liquid no matter how muchheat is generated by the fire. Evaporation from thesurface cools the liquid and hence the greater theheat absorbed by the liquid surface the faster liquidvaporises, and the more intense is the fire.

With flammable liquid mixtures, such as crude oilsand partially refined products, there may be veryhot layers of high boiling point residue at or nearthe surface, or even crusts of coke may form on theburning surface.

Water-miscible fuels require higher applicationrates due to their destructive effects on foams.Alcohol resistant type foams should always beused for these types of applications.

Problems are experienced with fully involvedcryogenic storage tank fires such as ethylene, LPGor other similar liquefied gases. To apply water orlow expansion foam to the liquid surface wouldcause it to warm up which in turn would increasethe evaporation rate and intensify the fire. Highexpansion foam can be applied to pool fires ofthese fuels when held in retention bunds, however,this is not the case for tank fires because this typeof foam cannot be projected any appreciable dis­tance. There is generally little alternative in thesecases other than to pump out as much of the tank

50 Fire Service Manual Firefighting Foam 51

______________________~ .....J!

7.5 Practical Scenarios

contents as possible, cool the tank to avoid col­lapse and allow the fuel to burn out under control.

(a) Example of Resources Required ForA Storage Tank Fire

The figures quoted below are based on a fire inci­dent involving a 45m diameter by ISm high crudeoil storage tank with nearby storage tanks thatwould require water cooling. The followingassumptions are made in order to demonstrate thesize of the logistic problem when using conven­tional equipment:

= 104 (2.6 km)

= 28Hydrant outlets(2 per monitor)

Lengths of 70mmhose (each 25m)

The figures above are for a 60 minute foam appli­cation period and a 4 hour water cooling period.During the firefighting period, assuming that cool­ing of the adjacent tank continues, the water flowsrequired would be approximately 11,500 Ipm forfoam production and approximately 13,000 Ipmfor cooling the adjacent tank making a total of24,500 lpm. In addition, the 3% film-formingfoam concentrate supply would be approximately360 litres per minute making the total amount ofliquid required during the firefighting phase of thisincident nearly 25,000 Ipm.

For the foam attack, 7 monitors would be fed from4 hydrants using 14 outlets and an estimated mini­mum of 24 lengths of 70mm hose to supply thepumps and 28 from pumps to monitors.

To supply this would require the following exam­ples of firefighting equipment:

• Monitors = 14(each 1900 Ipm, 7 foam monitors,7 water monitors)

• Pumps = 14(one per monitor, each pump 2250 Ipm)

For the cooling water, 7 monitors would be fedfrom 4 hydrants using 14 outlets and an estimatedminimum of 24 lengths of 70mm hose to supplythe pumps and 28 from pumps to monitors.

The following Sections discuss typical tank firescenarios, the decision areas and the techniquesthat could be used to deal with them.

Table 7.1 contains information on the minimumtotal volumes of 3% and 6% foam concentratesthat are required for tanks of diameter ISm, 30mand 45m when using the Home Office recom­mended minimum application rates.

••

= 70 I ,000 litres - 21,100 litres

= approximately 680,000 litres of waterfor foam making

= Total amount of foam solution- Total amount of foam concentrate

Total surface area of adjacent tank

= 679,900 litres

= 1,600 m2+ (tank height x tankcircumference)

= 1,600 m2 + (ISm x (2 x Jt x r))(where n = 3.142 and r = tank radius 22.5m)

= area of tank top + area of tank sides

= 3,712 m2

= 1,600 m2 + 2121 m2

= approximately 3,800 m2 total surfacearea of adjacent tank

= 3,100,800 litres

= 1/3 x 3,800 m2 x 10.2 Ipm/m2 x 240minutes

(*113 is assumed to be the proportion of thesurface area of the tank subject to directheat radiation from the fire, see thisChapter, Section 5 (b) (iii))

= approximately 3,101,000 litres ofcooling water

= 1/3* x total area of tank x waterapplication rate x cooling time

Total cooling water required for adjacenttank

Cooling Water Requirements ForAdjacent Storage Tank

• Total amount of water required for foamproduction

•

•= approximately 701,000 litres of foam

solution

= 700,800 litres

= approximately 1,600 m2 tank surfacearea

= application rate x application time x tanktop surface area

= 7.3 Ipm/m2 x 60 minutes x 1,600 m2

Total quantity offoam solution required

Total amount offoam concentraterequired

= Total foam solution x foam concentration100

= 21,030 litres

= 701,000 litres x 3100

= approximately 21,100 litres offoam concentrate

(more than 1050 drums, eachcontaining 20 litres)

= m 2 (where Jt = 3.142 and r = tank radius)

= 3.142 x (22.5m)2

= 1,591 m2

• it is assumed that cooling of the adjacentstorage tank is required for a total of 4 hoursto allow enough time for resources to be col­lected and the fire to be fought. Tank cool­ing continues during the firefighting period.

From this information, the following can be calcu­lated:

Firefighting Foam and Water Requirements

• Surface area of the top of the tank

•

•hydrants available at 80m intervals with4 x 70mm outlets;

a 3% alcohol resistant film-forming foam isapplied at the Home Office recommendedminimum application rate of 7.3 litres/min/m2 for a period of 60 minutes. Thisapplication rate assumes that all of thefoam produced is being projected onto,and reaching, the surface of the fire. Thisapplication rate, water requirements,foam concentrate requirements andhence the number of pumps, monitorsand associated equipment, may all needto be increased by up to 60% to take intoaccount foam that does not reach the firedue to losses caused by the effects of foamstream fall-out, wind, thermal up­draughts etc. (see Chapter 4, Section 2);

it has been assumed that the hose layout willbe idealised, i.e. the minimum number ofhose lengths needed to cover the distancesinvolved have been used:

exposure protection to an adjacent storagetank of similar size to be at the maximumrate of 10.2 litres/min/m2 (see this Chapter,Section 5 (b) (ii) for discussion of coolingrates for adjacent tanks - 2 litres/min/m2

may be more appropriate), the storage tankis approximately I tank diameter away fromthe burning tank;

•

••

•

52 Fire Service Manual Firefightillg Fuam 53

•

Table 7.1: Storage Tank Fires - Approximate Total Foam Concentrate RequirementsFor 60 Minutes Foam Application

J. The application rates that have been used to produce this table are the Hume Officerecommended minimum (see Chapter 4).

2. All foam application times are the Home Office recommended minimum of60 minutesfor storage tank fires (see Chapter 4).

3. No allowance has been made for ji)(J/I1 concentrate requirements for increased foam applicationrate during jire{ighting due to losses or for continued application after extinction. Losses could addas much as 60% to each of the above foam concentrate requirements (see Chapter 4).

4. Alljigures are approximate.

Approximate Total Foam ConcentrateRequirements For 60 Minutes Application (litres)

Tank Surface Recommended FP AFFF FFFP AFFF-AR FFFP-ARDiameter Area of Usage

Top of ConcentrationTank

(m) (m2) (%)

15 180 3% 2,600 2,200 2,200 2,200 2,200

6% 5,200 4,300 4,300 4,300 4,300

30 710 3% 10,300 8,400 8,400 8,400 8,400

6% 20,500 16,700 16,700 16,700 16,700

45 1,600 3% 26,000 21,100 21,100 21,100 21,100

6% 51,900 42,100 42,100 42,100 42,100

Notes to Table 7. J .'

The area of an adjacent tank that requires coolingdue to exposure to heat and flame is often estimat­ed at between 25% and 50% of the tanks total sur­face area depending on its separation from theburning tank. For instance, for adjacent tanks atonly I diameter spacing, an estimate of 1/3 of thetank surface requiring cooling is reasonable. Fortanks that have closer separations, more of the sur­face area of the exposed tank would require to becooled.

order to minimise these problems, the aim of cool­ing water application should be to only applyenough to generate steam from hot surfaces andnot to totally flood the adjacent tank and bundarea.

Obviously, the amount of water and equipmentrequired for cooling can increase dramatically if atank fire boils over. In this situation, not only areflames likely to get nearer to, or even engulf tankswithin the same bund, but the heat from the flamesmay also begin to affect tanks in other, adjacentbunds.

The quantities of water that can be successfullydelivered by portable monitor nozzles to adjacenttanks wiIJ vary depending on wind speed, winddirection, nozzle type, pressure, distance of throw,monitor position and so on. In addition, portablemonitors tend to deliver water in a less even pat­tern than fixed spray nozzles. However, it is possi­ble to direct portable monitors more preciselytowards the areas of adjacent tanks most affectedby the heat and flame of a burning tank.Alternatively, oscillating water monitors will pro­vide a wide and even area of cooling water.

Pressurised tanks, such as butane spheres shouldbe cooled to avoid excessive operation of the safe­ty relief valve and to maintain a temperature mar­gin in case of a later boil-over. Many pressurisedtanks have fire protection cladding or fixed sprayprotection systems. This should be confirmed withthe refinery management to ensure that the mostappropriate cooling action is taken.

It is useful if a fire protection engineer is availablewith a radiation calculation software programmeto make estimates of incident radiation and adviseon cooling.

Generally, the NFPA cooling requirement is alsooften used as a guide for the use of portable moni­tors in tank cooling applications and has been usedin the calculations in this Chapter and in Chapter8. However, this water cooling rate is consideredby many experienced firefighters and petrochemi­cal organisations to be excessive for the protectionof atmospheric hydrocarbon storage tanks wherethey are more likely to be subject only to radiatedheat. They see this as diverting resources of organ­isational time, equipment and water from a possi­ble foam attack, and contributing to difficultground conditions in the area surrounding the fire.If tank spacing is adequate, cooling can nonnallybe kept to a minimum and resources should beconcentrated on making a successful foam attackeven if cooling water requirements are cut back inthe process. However, cooling of pressurised andexposed atmospheric tanks cannot be neglected,particularly during prolonged pre-burn periodswhilst a foam attack is being organised.

NFPA (US National Fire Protection Association)recommend a water cooling rate for direct flameimpingement of exposed adjacent LPG pressurevessels of 10.2 Ipm/m2 when using fixed protec­tion water spray systems.

(iii) Cooling an Exposed Tank

Care should always be taken to ensure that coolingwater does not enter the tank because this willbreak down the foam blanket and may speed theonset of slop-overs and boil-overs (see Section(xiii) below).

Experienced firefighters suggest that a water cool­ing application rate of 2 Ipm/m2 of the surface areaexposed to radiated heat is adequate for this purposeand is a more realistic figure for use in preplanningwater requirements. Atmospheric tanks beyond 1.5times the diameter of the tank on fire may notrequire cooling unless the fire plume is blowntowards them. However, if water sprayed onto adja­cent tanks immediately turns ('flashes') to steam,then cooling should commence immediately.

The use of too much cooling water for adjacenttanks can lead to supply flow and pressure prob­lems for the foam attack, overloading of drainagesystems and can lead to unwanted fuel spread. In

I I,

I

I

necessary if the tank begins to buckle. Excessivebuckling could result in the rim curling inwards,touching the fuel surface and preventing an even­tual foam blanket spreading over the entire liquidsurface. Cooling water should be sprayed as even­ly as possible around the rim. This will help toavoid uneven cooling which may cause even moredistortion of the tank rim.

Cooling of the ullage of the involved tank is nec­essary dUling the foam attack to help reduce thetemperature of the metal surface against which thefoam is attempting to seaL

Oscillating water monitors will provide a widerarea of cooling water coverage around the ullageof the burning tank than is possible with fixedmonitors. They are preferred in instances wherecooling needs to be carried out from within thebund because they can be left unattended.

(i) General

(b) Techniques and Decision AreasWhen Tackling Storage Tank Fires

(ii) Cooling the Involved Tank

The following Sections outline some of the possi­ble complications that can occur when fightingstorage tank fires and the decision areas that needto be considered. Ideally, many of these problemareas would have been considered and decisionsmade in the preplanning that should have takenplace in anticipation of storage tank incidentsoccurring. Information is also given on specialtechniques that could assist firefighting operationswhen using foam to extinguish storage tank fires.

It is only worthwhile cooling the ullage area of thetank involved in fire (i.e. the area of the tank edgeabove the level of the burning fuel). This may be

54 Fire Service Manual Firefighling Foam 55

(iv) Water Supply

(v) Marshalling Equipment and Materials

A pre-plan should be available showing the quan­tity of firefighters, equipment and materials neces­sary to mount a foam attack. Calculations such as

r57Firefighting Foam

Base injection of foam will also induce circulationto some degree.

(viii) Circulation

Circulation will disrupt the surface of the burningfuel. Consequently, in order to allow a foam blan­ket to be formed and to spread evenly and quicklyacross the surface of the fuel, circulation should bestopped prior to the application of foam.

If a hot layer is advancing down to the level whereit may encounter water, it can be useful to attemptbreakage or dispersion by means of tank stirrers (iffitted) or by injection of cold product, inert gas, airor other fluid. However, the possible need for cir­culation will not arise until an advancing hot layerhas been formed which is likely to be several hoursafter ignition.

(ix) Pump outlPump in

must be stressed that these methods wiIJ only givean indication of the formation of hot layers, theymay not be uniform in cross-section and may onlybe formed in the centre of the tank giving little orno indication at the outer edges. (see also sub- sec­tion xiii below)

(x) Mounting a Foam Attack

The argument for pumping out product is both thatthe financial loss is reduced to some extent andthat the tank will burnout in a shorter time. If thereis no possibility of mounting a foam attack, this isa reasonable objective. There is a risk however thatthe tank rim wiIJ curl in when liquid levels are low­ered, impeding any eventual foam attack.However, if there is confidence in the chance ofthe success of a foam attack, it can be argued thatpumping product into the tank is a useful means ofpreventing the tank from curling over.

Resources should not be wasted by "trying a littlefoam to see what happens". A foam attack shouldonly be mounted when sufficient resources areavailable to maintain it at the required applicationrate continuously for at least 60 minutes. Stoppingfoam application before the fire has been com­pletely extinguished will probably lead to a rapidburnback and destruction of the whole of the foam

(vii) Temperature Monitoring

FP foams exhibit good heat resistance properties,such as edge sealing and burn back resistance butare less effective at lower expansions than AFFF,AFFF-AR, FFFP and FFFP-AR.

Ideally, primary aspirated foams for tank fireapplication should be used at an expansion ratio of6: I or more and should give a 25% drainage timein excess of 2 minutes in order to have effectiveheat resistance properties.

The AFFF and FFFP group of products only formaqueous films on certain hydrocarbon fuels. Inlarge tank fire situations, the types of fuel storedand the way in which they burn, generally preventsthese foams from forming films on the surface ofthe fuel although the ability of these foams to read­ily flow across the fuel surface can produce quick­er flame knockdown.

FP, FFFP and FFFP-AR foams tend to form crustswhere the foam blanket is directly exposed to heat.This reduces their ability to flow and may producesealing problems at the tank edges.

AFFF and FFFP foams drain much quicker thanthe alcohol resistant versions of these and FPfoams~ this can be seen as both an advantage and adisadvantage. This faster drainage is believed tocontribute to rapid flame knockdown but may alsoreduce the protection offered by the foam blanket.As a result, constant replenishment of the foamblanket will be required during the fire as will fre­quent re-application after extinguishment to assistin preventing reignition. For fuels such as crudeoils, faster draining foams may help to cool thefuel quicker but are also more likely to cause slop­overs and boil-overs.

For tanks containing burning crude and heavy oils,it is important to monitor the progress of any hotlayer formation. This can give an early warning ofpotential boil-over (see Section (xiii) below). Arough indication is provided by peeling paint onthe tank side or by the steam generated when thetank side is wetted. More accurate indications canbe obtained by the use of thermal image camerasor from heat sensitive paint if it has been appliedin a vertical line down the tank side. However, it

Ideally, it should be possible to assemble anddeploy this equipment with the required firefight­ing teams within 2 hours of the alarm. In practice,the logistical problems probably make 4 hours amore realistic target. The foam attack should notbe started until the full range of equipment andmaterials required is available on site. There aremany cases where resources have been wasted onpremature piecemeal efforts.

It is assumed that cooling water is applied to theadjacent tank at a rate of 10.2 Ipmlm 2 over onethird of the surface area of that tank (2 Ipm/m2 maybe a more appropriate rate, see this ChapterSection 5 (b) (iii) for further information). The cal­culations do not include the equipment and waternecessary to cool the ullage of the burning tank. Itshould also be noted that the application rate (7.3litres/minute/m2), water requirements, foam con­centrate requirements and hence the number ofpumps. monitors and associated equipment, mayall need to be increased by up to 60% to take intoaccount foam that does not reach the fire due tolosses caused by thermal up-draughts etc. (seeChapter 4, Section 2).

• 14 monitors (each 1,900 Ipm, 7 water,7 foam)

• 104 lengths of hose (70mm, 25m)

those earlier, in Section 5(a), show that for a 45mdiameter by 15m high crude oil storage tank thefollowing are required as a minimum during a 60minute foam attack and simultaneous cooling of anadjacent tank:

• 7 inductor systems for foam monitors

• 21, 100 litres of 3% concentrate

• 7 foam dams

• 14 pumping appliances (each 2,250 Ipm)

(vi) Foam Types

A review of the various types of foam concentratesavailable, and the characteristics and properties offinished foams are discussed in Volume I.

Fire Sen'ice Manila!

Apart from pressurised vessels, all cooling watercan be switched to the foam attack if necessary inorder to achieve the required application rate.

In some cases, the on-site fire pumps and mainscapacities at UK refineries are sufficient to meetthese high demands and in others they are not. Themost common deficiency seems to be the under­sizing of fire mains in storage tank farm areaswhich are often remote from the fire pumps.Hydrant mains should be capable of supplying themaximum f10wrates required at a residual pressurein excess of 2 bars with a single section of mainout of service in the hydraulically least favourableposition.

The total volume of water used for cooling can befar in excess of that required for the foam attackdue to the longer duration that can be involved inwaiting for resources to arrive. Where there is aneed for extended periods of cooling, it is usuallynecessary to complement or replenish any on-sitewater supply system with a water relay from anestuary, lake or other natural "unlimited" watersource.

In some areas, fire brigade pre-planning exerciseshave highlighted deficiencies in supply whichhave been remedied by plant/refinery manage­ment. Fire hydrants should ideally be of the aboveground type with four gated 70mm outlets and asingle 100mm, 125mm or 150mm outlet. In addi­tion, the fire main should ideally be below ground,with below ground isolation valves, to provideblast protection. Some UK refineries have largecapacity transportable pumps, with capacities ofup to 23,000 lpm, which can be used to supple­ment any short falls from the fire main.

Brigades should try to ensure that, on at least ayearly basis, all plant/refinery mains are thorough­ly flushed through and all outlets are checked forcorrect operation.

56

L

blanket with a complete waste of the resourcesalready committed.

Care should always be taken when fighting tankfires to ensure that there is sufficient ullage in thetank to contain prolonged applications of firefight­ing liquid. Pumping out some of the contents of thetank may need to be considered (see this Chapter,Section 5 (b) (ix»).

When applying foam to a storage tank fire, thestream from the monitors should be aimed at thedarkened area just above the rim of the tank, andbelow the flames in the fire plume, where air isbeing sucked in to the fire. This will help toensure that the foam is applied directly to thesurface of the fuel and not taken up by the ther­mal updraft of the fire as may be the case if thefoam were applied directly in to the fire plume.If possible, the rear of the foam landing areashould be positioned within 25 metres of theback edge of the tank. In any case, the momen­tum of the foam stream as it strikes the burningfuel will push the foam blanket towards thisdirection. All of this will assist in forming a bitewhich will be supplemented once foam spreadsto, and begins to build up from, the back edge ofthe tank. Cooling of the ullage at the rear of thetank will assist in quickening the formation of afoam blanket here.

On larger storage tanks, foam monitors may needto be positioned to have overlapping foam landingareas in order to ensure that a high enough localapplication rate is achieved in order to form a'bite' (see Chapter 5, Section 2 (a) (iv) and that allareas of the fuel surface can be covered by theflowing foam. The most difficult area of the tankto extinguish will be the area at the front of thetank, nearest to the monitors. Due to the long fuelburning time in this area, the tank rim will beextremely hot and cooling of the ullage here willhelp the foam blanket to form a seal. However, itis likely that by the time the edge of the foam blan­ket has flowed against, and across, the burning fuelto reach the tank sides in this area, it will have seri­ously degraded and will not be immediately capa­ble of forming a seal. Consequently, further foamapplication is required in order for a fresher wall offoam to be pushed in to that area to make a finalseal.

It has been estimated that foam, when applied tothe suIface of a burning hydrocarbon liquid, canspread from the edges of its landing area a maxi­mum distance of 30m although a maximum of25m may be a better approximation to use opera­tionally. Obviously, the spreading distancedepends on the type of foam used. The more fluidfoams, such as the film-forming types, are morelikely to spread over these distances than the stifferP and FP foams. Tactics which produce a circularmovement in the foam blanket on the surface of afoam blanket have also been reported as assistingin foam spread (see this Chapter, Section 5 (b) (xi)below).

A substantial bite should be obtained within thefirst 20 to 30 minutes of a foam attack. If the attackhas not succeeded or made significant progress bythis time (i.e. a bite has not been formed) thenthere are probably other factors mitigating againstthe firefighters and the attack should be reassessed.In particular, application rates and tactics shouldbe reviewed. If necessary, the foam applicationshould be stopped in order for further resources tobe gathered together before attempting a furtherfoam attack. The resources used during this initial20 to 30 minute attack will also need to bereplaced.

The only equipment permitted within the bundshould be ground monitors where no other saferposition will allow their streams to reach the tank.It is important that firefighters are not allowed toremain in the bund due to the risks from boil­overs, slop-overs or a split in the tank.

If possible, monitors in the bund should be mount­ed above ground level so that any liquid collectingin the bund does not affect their operation.

(xi) Special Firefighting Techniques

Two techniques are strongly suggested by thosewho have fought large tank fires. Firstly, the valueof using water spray above the foam blanket tocool the fire plume and take away some of the backradiation. If monitors run out of foam they shouldbe raised to contribute to plume cooling. The waterwill largely evaporate in the plume and experienceshows that, at the right elevation, this tactic doesnot disrupt the build-up of the foam blanket.

Secondly, it is said that the foam blanket can bespread over the surface more rapidly if a slowswirling motion is imparted by placing one of themonitors to land slightly off centre of the liquidsuIface. This technique is advocated in conjunc­tion with any foam.

(xii) Increasing the Range of Foam Monitors

The ability to tackle storage tank fires depends toa large extent on the elevation and range of thefoam monitors available. Manufacturers literatureis often very short of this type of information andthe use of different elevations and operating con­ditions makes comparisons very difficult. Pre-pur­chase trials of monitors on the type and size of tankto be protected are often the only sensible meansof ensuring that their performance is adequate.These trials should also take into account the vari­ations in heights and distances of the monitors inrelation to the tank due to the surrounding bundwalls. The possibility of being able to use thesemonitors under various on-site wind speed anddirection conditions should also be considered.

Factors that can increase the monitor range andtrajectory height include:

• Reducing the Expansion Ratioof the Foam

For large storage tank fires, expansion ratios of 4 to6 are preferred for AFFF and AFFF-AR. One of thebenefits of these Jow expansions is the increasedthrow that can be achieved. The preferred expan­sion range for fluoroprotein foams is 6 to 8.

Lower expansion ratios are also believed to assistfoam in penetrating the thermal updrafts producedby large tank fires; foams with higher expansionratios are more likely to be carried away up in tothe fire plume.

• Increasing the Pump Pressure

Increasing the pump pressure leads to a higherpressure at the monitor and hence a longer throw.Generally, fire service low pressure pumps areoperated at around 7 bar but they can be safelyoperated at up to 10 bar if extra throw is required.However, increased pumpjng pressures do not pro-

duce a proportional increase in jet range becauseof air resistance factors. They may also lead to abreak up of the jet at the monitor which may resultin a lessening of the throw.

• Reducing the Distance From Pump toMonitor

Pressure drops through the hose used to connectpumps to monitors can greatly reduce the pressureat the monitor and hence reduce its throw.Reducing the length of these hose runs will reducethese pressure drops as will increasing the hosediameter.

• Higher Capacity Monitors

Manufacturers quote improvements in range withincreasingly higher capacity nozzles. For instance,one manufacturer quotes a range of 50m and amaximum height of l8m for a 1,820 litre perminute nozzle and a 54m range and 22m height fora 2,700 litre per minute. Both are of the samedesign with a recommended operating pressure of7 bar.

• Minimal Obstructions in NozzleWaterways

Some foam-making monitors include baffles andgauzes to increase the amount of air mixing of thefoam solution that takes place. This can signifi­cantly reduce the throw of these monitors althoughmore consistent quality finished foam is produced.

• Changing Foam Induction Method

In-line venturi inductors generally cause pressuredrops of at least 30% and are sometimes in theregion of 40 to 50%. The pressure drops can begreater than this, and the inductors may fail topick-up foam concentrate, if the inductors are notcorrectly matched to the monitors. There are othermethods of foam induction available that causemuch smaller losses in pressure in the delivery lineto the monitors (see Volume I).

• Elevation of Monitors

Elevating monitors above ground level can obvi­ously assist in applying foam over tank walls.

58 Fire Service Manual Firefighting Foam 59

Whilst elevated platforms and cranes can achievethe best means of doing this, significant advantagescan be gained by mounting monitors on bunds orbund extensions. A 3m high bund can make at leasta 10% improvement on the height of the jet trajec­tory. However, elevating monitors may cause fur­ther throw problems due to head pressure drops. Insome cases, such as with venturi type in line induc­tors, these pressure drops may prevent the induc­tion system from operating correctly.

(xiii) Boil-overs, Slop-overs and Froth-overs

If there is water in a fuel storage tank, either in theform of a stratified layer of moisture (crude oilsmay contain up to 5% by volume of water) or, asis often the case, up to a metre or so of water in thebase, or even trapped higher up in a pocket creat­ed by a sunken floating roof, then there exists thepossibility of sudden violent steam generation. Theresultant rapid expansion as the water is convertedinto steam can result in the phenomenon known asboil-over, i.e. the burning contents of the tank willbe thrown out. This may occur after a tank fire hasbeen extinguished with the risk continuing until allof the contents of the tank have been cooled to

below 100°C.

Boil-avers are very large events, during which sub­stantial quantities of flammable liquid, possiblyeven the full contents, are ejected from an open tankand onto the surrounding area. The radiated heatproduced during a boil-over is extremely intense.

Boil-avers only happen after long pre-burn periodsin wide range f1ashpoint fuels such as crude oil.They occur when a hot layer of residue forms atthe top of the tank and, due to its density, sinksbelow the un-burnt contents of the tank. This hotlayer can be at temperatures ranging betweenapproximately 150°C and 300°C. The hot layer isnot even and may have deeper waves travellingdown from it. The rate at which the hot layer trav­els down the tank varies depending on the type ofcrude product but can range from 0.075m to 1.25mper hour. For most crude oi Is, the rate of traveldown the tank is generally between 0.3m and 0.6mper hour. Thermal image cameras can be used totrack the progress of travel of a hot layer. as canobserving where water is flashing to steam off thesides of a burning tank. However, it must be

stressed that these methods will only give an indi­cation of hot layer formation, the zone may not beuniform in cross-section and may only be formedin the centre of the tank giving little or no indica­

tion at the outer edges.

Once the hot layer reaches water further down thetank, a steam explosion can occur where the waterflashes to steam and the volume of the waterexpands by approximately 1700: I. This violentlypropels the burning liquid above it upwards andoutwards from the tank.

It has been estimated that a steam explosion canpropel the contents of a tank to a height of10 times the diameter of the tank. Incidents haveoccurred where the tank contents have beenestimated to have been projected to heights of up

to 300m.

The presence of steam in the ejected oil canincrease its volume temporarily by several multi­ples to form a 'froth' allowing rapid spread of upto 7 tank diameters away from the tank. It is likelythat this ejected oil would flow over the contain­

ment bunds of the tank.

Boil-avers can occur with very little warning andtheir far reaching effects should be taken in toaccount when positioning personnel and equip­ment. During 1982, a storage tank fire in Venezuelaburned for 6 hours before boiling over and killingmore than 150 people; 40 of them firefighters.

It is not uncommon during the initial stages of aboil-over for the tank to be lifted off its founda­tions and for product to flow from the base of thetank. The product may then continue to leak after

the boil-over has subsided.

Typical signs of an impending boil-over are:

• small amounts of burning product beingejected from the tank;

• an increase in the intensity and the height offlames in the tank;

• a 'frying' sound coming from the tank;

• a lightening of the smoke.

Slop-avers occur when some burning liquids, suchas heavy fuel oils or crude oils, become extremelyhot, any applied water may begin to boil on contactwith the fuel, the resulting rapid expansion as itconverts to steam may cause burning fuel to over­flow its containment and the fire to spread.

Froth-avers are where a non burning flammableliquid overflows from a tank due to the thermalexpansion of the liquid or violent boiling on top of,and within, the upper layers of the liquid due to thepresence of small quantities of water. This boilingmay produce a sufficient increase in the volume ofthe flammable liquid for a froth-over to occur.Froth-avers will generally only occur in wideflashpoint range products. such as heavy crude oilsand bitumen type products.

Boil-avers, slop-avers and froth-avers can allresult in hot, often burning, fuel being ejected froma storage tank and into the surrounding bund.Consequently, all deployment must be carried outwith the need in mind for a sudden evacuation offirefighters (and if possible of appliances and otherequipment) if a boil-over, slop-over, froth-over ora split tank should occur. Not only is there a riskfrom the heat radiation from any burning fuel butalso from the wave of expelled liquid which couldflow over the bund walls.

(xiv) Continued Application After Extinction

After extinction of the fire. foam applicationshould continue in order to keep the foam blanketintact and to help to cool the contents of the tank.

Crude oil that has been burning for several hourswill be very hot and will bubble through the foamblanket after extinction and pose a very severereignition risk. Continuous application of foamwill help to maintain the foam blanket. In addition,liquid draining from the foam blanket will cool thecrude down to reduce bubbling and prevent reigni­tion. Foam application made need to continue fortwo to three hours after extinction to ensure thatthe incident is fully under control. It should benoted that during this phase, boil-avers may occur.

Re-ignition may also occur from falling pieces ofglowing coke that may have formed on any over­hanging metal work. This has been known to

occur up to six hours after extinction had beenachieved.

Further cooling water may also be needed to coolthe external sUIfaces of the tank and hence help tocool the contents of the tank although this is not al?articularly efficient use of resources. Continuedcooling of the ullage area of the tank will help thefoam blanket to maintain a seal against the edge ofthe tank.

(c) Floating Roof Storage Tank FireScenario

This description is of a scenario which develops into a fully involved tank fire in a 45m diametercrude oil storage tank sharing a bund with a secondcrude oil tank of similar size, 45m (I tank diame­ter) distant from the first tank.

It is likely that a floating roof storage tank firewould start by a source of ignition (a lightningstrike or burning ember for example) setting fire tothe rim seal area.

Floating roof storage tanks catch fire less oftenthan fixed roof tanks with a flammable vapourspace, but there have been a considerable numberof such fires world-wide, and a larger number stillof rim seal fires most of which are usually extin­guished before they become more serious.

The alarm would be raised normally by visualsighting of smoke. which could involve a consid­erable delay at a remote unattended tank farm.Some floating roof tanks are equipped with auto­matic rim seal firefighting systems, others withvarious detection systems.

Once the alarm was raised the plant fire brigadewould respond and the local fire brigade wouldrespond in support. At this stage, it may not beimmediately apparent from ground level whetherthe fire is confined to the rim seal area or involvesthe full fuel surface. Obviously, the extent of theincident must be determined immediately onani val.

The options then depend on the equipment avail­able. If rim seal foam pourers are provided theseshould be used. Some installations provide for a

Firejighling Foam60 Fire Service Manual61 f

__________________________~ti ..JI

supplementary foam hose to be attached to thefoam pourer system so that the firefighters can infill any gaps in the foam coverage from the pour­ers by manual application from the wind girder.

Cases are quoted of rim seal fires being extin­guished by foam hoses dragged up the externaltank stairway and by large dry powder extinguish­ers being used from the wind girder.

This last practice appears both uncertain and dan­gerous. The range of dry powder extinguishers islimited and, if the floating roof is low, it is unlike­ly that they would be effective at the distancesinvolved. Furthermore, with an exhaustibleresource such as an extinguisher it is possible thatit will run out whilst the firefighter is distant fromthe access stairway. Lf the rim seal fire should thenburn back he could be cut off from the only meansof escape without any firefighting resource toassist him.

The dangers of vapours on the roof should alsobe taken into consideration.

However, combined dry powder/water (or sec­ondary aspirated foam) hand-held branches areavailable. These enable dry powder to be fireddown the centre of the water/foam stream whenrequired, increasing the reach of the dry powder by3 or 4 times to around 12 metres. This equipmentmay be suitable for this type of applicationalthough suitable large dry powder extinguisherswould need to be positioned relatively near to thebranch (often within 30 metres). In addition, theproblems in dragging two hoselines (onewater/foam, one dry powder) up an external tankstairway would need to be considered.

The progress of a fire from the rim seal stage canbe quite rapid or it may develop very slowly. Iffloating pontoon sections are not fully air tight,these may contain an explosive mixture of gas andair. An explosion in a pontoon section could rapid­ly sink or tilt the roof exposing the crude oil sur­face to the spread of flame.

Once the tank becomes fully involved, the fullscale emergency plan should be brought intoaction.

(d) Fixed Roof Storage Tank Scenario

A fully involved fire in a fixed roof storage tank isin many ways similar to the floating roof storagetank case in that deployment of large resources arerequired.

The first difference lies in the lead up to a fullyinvolved fire. The vapour space above the liquidcan contain a flammable gas/air mixture when anatmospheric tank has been partially emptied.Faulty conservation vents or flame arrestors cou­pled with an ignition source, or simply a lightningstrike, can cause an explosion in the vapour space.In some cases the roof is blown clear of the tank,splitting at the weak roof-ta-shell seam, in othercases a gash in the roof-ta-shell seam allows theexplosion to vent leaving a narrow aperture for fireto escape and firefighting media to enter.

In terms of fixed equipment, top pourers are use­ful if serviceable but tend to become damaged inany initial explosion. For these types of incidents,base injection systems come into their own. Thereis not the same internal obstruction as with a par­tially submerged tloating roof, and foam injectedinto the product inlet line or directly into the tankcan generally rise through non water-misciblecontents and spread to a certain extent over thesurface. With larger tanks of a diameter in theorder of 45m, there is still a need for over-the-topmanual application of foam to support the baseinjection. For water-miscible or waterlogged tankcontents, it may be necessary to rely entirely onover-the-top application, although semi-subsur­face base injection (floating hose) systems may beappropriate.

Whilst FP foam is effective on smaller diametertanks, there is some question about its ability tospread over the greater distances required in tack­ling larger tank fires. This is of particular concernhere because in cases where only restricted aper­tures are available for foam application, there is lit­tle that can be done by manipulation of the jets andtheir landing area to aid foam spread, and thespreading characteristics of the foam may becomea critical factor in determining how large a fire canbe extinguished. Even with film-forming foamconcentrates, the absolute maximum spreadingdistance from the edge of the foam landing area is

estimated to be in the region of 30 metres althougha maximum of 25 metres is more likely.

Firefighting through a restricted aperture alsomeans a greater heat radiation hazard for fire­fighters. The fire plume on leaving the tank canbe deflected by 60° or more from the vertical bythe size and position of the aperture. Monitorteams will need to be positioned in the same tankquadrant as the fire plume is directed in order toaim jets through the aperture. Special care shouldbe taken that crews are well protected againstsudden increases in heat radiation. One methodused on certain specialist nozzles is to have thefacility to switch a stream from jet to wide-anglespray with a quarter turn of a control handle. Thismay reduce radiation sufficiently to allow teamsto hold their position during a brief flare, or tocover their retreat in a more prolonged surge infire activity.

Fire teams tackling tank fires through aperturesalso have little choice in their position relative tothe wind, and adverse wind conditions could makemost useful positions for ground monitors unus­able. In these cases it may be possible to deployhydraulic platforms and transportable foam towersto discharge foam over the aperture lip to augmentfoam from monitors.

In the case of hydrocarbon liquids with a flashpoint above the storage temperature, tests haveshown that the fire can be extinguished, or at leastits intensity reduced. by rapidly rolling colder liq­uid from the lower part of the tank to displace theheated top surface. The most practical way ofachieving this is to inject air into the bottom of thetank. As the air rises in the tank. it pushes colderliquid to the surface. With refined high flash pointproducts the heated surface layer has very limiteddepth regardless of the length of burning. and airagitation is one way of extinguishing the fire. Inthe case of high flash point crude oil the agitationmust be done before the heat wave has penetratedtoo deeply into the surface of the oil.

Low flash point products on the other hand cannotbe extinguished by cooling alone. However, airagitation will reduce the intensity of the fire andwill assist other forms of extinguishing such asfoam or dry powder.

(e) Storage Tank Bund Fire Scenario

This example considers a fire in a bund area sur­rounding two, 45m diameter petrol tanks, each15m high. If the separation distance is one diame­ter between the tanks, then the minimum bunddimension would be 170m long by 80m wide. Thiswould give a bund area of 13,600m2 reduced to12,000m2 after deducting the area of the unaffect­ed tank, or effectively I1 ,500m2 allowing for a 45°slope on the face of the bund walls.

To provide the recommended 110% retentioncapacity of the largest tanks' contents, the heightof the bund would be 2.2m giving a total bund vol­ume of 25,300m3 compared with the maximum23,000m3 capacity of one of the tanks.

Bund fires are very often limited in area and con­stitute spreading/running/spill fires. In these casesthe response is generally to lay foam and use waterspray to allow access to isolation valves and to cutoff the spreading/running fire element. The spillarea is then calculated and a foam attack is mount­ed when sufficient firefighters, material and equip­ment are available to provide 4 to 6.5 litres/min/m2

(depending on the foam concentrate in use) andsustain application for 60 minutes (see Chapter 4).Tank cooling during the mobilisation periodshould be avoided if possible since the run-offwater will tend to spread the burning liquid over alarger area. However, if the tank contents are low,and there is direct flame impingement, coolingmay be necessary.

An area for particular attention in such small scalebund fires is any gas or liquid lines within the bundarea which may be exposed to fire. If not fireproofed, they will require protection with prefer­ably a local foam blanket, or less desirably, withwater spray.

In some bunds, small retention walls are providedto assist in controlling limited spills. For example,in cryogenic storage tank bunds the valve area isoften provided with a small bund-within-a-bundwhich drains to a small catchment pit in the cornerof the main bund.

Fully involved bund fires following a majorspillage are rare, but do occur, particularly as a

62 Fire Service Manual Firefighting Foam 63 ~

______________________________~ ---'olJ

Firefig ling oam

• 3% foam concentrate requirement

To mount a 60 minute foam attack on the bunddescribed above using 4 Ipm/m2 of a film-formingfoam would require:

result of boil-over, and sometimes following a ter­rorist, or military attack. In these cases, the risk ofrupture of the second tank is the major concern. Ifbund drainage facilities are adequate, it may bepossible to cool this tank with water spray whilstthe foam attack is being prepared. When sufficientresources have been assembled to mount a foamattack, the area around the un-ruptured tank shouldbe tackled first. Tank walls can be used as back­plates to break the jet momentum and run foamonto the liquid surface whilst a blanket is simulta­neously built up from the bund wall outwards.

number of monitors required;

number of fire service pumps required;

total quantity of foam concentrate requiredfor 60 minute foam attack;

number of hydrants required;

2,250 Ipm pumping appliances;

70mm hose in 25m lengths;

••••

• 1,900 lpm monitors;

• lengths of 70mm hose required.

The main items of conventional fire service equip­ment assumed to be available are:

••

In Chapter 7, information was given on the practi­cal aspects of dealing with storage tank fires whenusing conventional fire service equipment.Particular reference was made to fighting fires intanks of up to 45m in diameter.

This Section examines, in more detail, the resourcesand logistics involved in a typical deployment ofconventional fire service equipment to deal withstorage tanks of 45m and beyond in diameter. Thisis followed by a discussion of other, larger equip­ment, that is available and the reduction in logisticalproblems that the use of these can bring.

Chapter 8 - Logisitics of Dealing WithLarge Storage Tank Fires

8.1 Introduction

(a) General

8.2 Convcn ional Fire ttack

If difficulties are encountered in projecting thefoam to the centre of the bund, then a longerduration of supply may be needed. Thus thedimensions, shape and access to a bund must alsobe considered.

practical difficulty, and alternative techniques arediscussed later.

Further information and guidance will be found inFire Service Manual, Volume 2, Fire ServiceOperations - Petrochemicals.

Foam solution requirement per minute

= 48,000 Ipm

Total foam solution requirement

= 4lpm/m2 x 12,000m2 sLllface area of bund

= 48,000 Ipm x 60 minutes

= 2,880,000 litres

•

•

This Section highlights the difficulties faced whenusing conventional equipment to fight flammableliquid storage tank fires of 45, 60, 75 and 90 metrein diameter. Tables 8.1 to 8.11 provide the follow­ing estimates for each of these tank sizes:

The logistical problems of using conventional fireservice equipment to tackle large tank fires are sig­nificant. Although some brigades and petrochemi­cal plants possess specialist equipment to deal withthese types of fire, in many instances, only stan­dard fire service equipment is available.

= 2,880,000 litres x 0.03

= 86,400 litres

This would require equipment to the extent of atleast:

• 22 x 2250 Ipm pumps;

• in excess of 400 lengths of hose (lOkm);

• a water supply capable of providing48,000 Ipm at 6 to 7 bars.

The likely shortage of hydrant outlets wouldnecessitate more hose lengths per pump than in thefloating roof tank fire case (above). No allowancehas been made in these quantities for replenishingthe foam blanket. Parking and layout of 70mmhose on this scale becomes a considerable

•••

quantity of water required per minute forfoam attack and for cooling;

quantity of foam concentrate required perminute;

total water usage for a 60 minute foam attackand 4 hours of water cooling of adjacent tanks;

• venturi type in-line inductors.

It should be noted that the deployment of equip­ment shown in the tables is theoretical and approx­imate, they are based on the Home Office recom­mended minimum application rates (see Chapter4) and do not represent practical experience. Thereare few instances where storage tank fires of diam­eter 45m to 90m have been successfully extin­guished. Those claimed have been achieved withthe use of specialist equipment (see this Chapter,Section 3).

The tables should be used purely as a means ofcomparing the practicalities of conventionaldeployment as against use of specialist equipment,rather than as a model for strategic planning. Itshould be noted that 1,900 Ipm monitors may nothave sufficient range to project foam in to tanks ofthis size.

64 Fire Service Manual Firejighfing Foam 65

ti

The tables do not take account of the number offirefighters required to deploy equipment. Forlarge fire incidents, many more personnel may berequired than would be provided with the mini­mum number of appliances shown. Relief crewsmay be required, and many firefighters may bedeployed in establishing a chain of foam concen­trate supply, or in setting up hose runs to draw suc­tion from natural water courses. It is recognisedthat these firefighters will be transported in fireappliances, but these appliances would not neces­sarily form part of the attack team.

It is also assumed that firefighting depends entire­lyon over-the-top projection of foam by firebrigade monitors. There are cases where fixed sys­tems around the tank rim or for base injection offoam will be available and could be used to advan­tage, but such provision is by no means certain.Even if these fixed installations are available, theymay have been incorrectly maintained or may havebeen damaged during the incident thus makingthem inoperative.

The other assumptions made when producingthese tables are discussed below.

(b) Cooling Water

The NFPA recommended cooling rate of 10.2Ipm/m2 (see Chapter 7, Section 5 (b) (iii) for dis­cussion of cooling rates; a rate of 2 Ipm/m 2 may bemore appropriate) has been used in the calcula­tions presented in Tables 8. I to 8.1 J in order torepresent a 'worse case' situation in terms of cool­ing water resources needed. Water can also be use­fully used to cool the external ullage of the tank onfire during foam appl ication (see Chapter 7,Section 5 (b) (ii». The water requirement for thisadditional cooling has not been specifically includ­ed in the calculations presented in Tables 8.1 to8.11 but should be more than covered by theresource requirements calculated from the 10.2lpm/m2 cooling water application rate.

(c) Bund, Hydrants and Hose

In order to give an indication of the quantities ofhose required, it has been necessary to make someidealised assumptions about the tank, bund andmains layout. It has been assumed that the bund

configuration allows space at the corners of bundsfor vehicles and fire appliances to stand duringoperations, whilst leaving bund roadways clear.Road widths are assumed to be 10m to permit bothhose laying and vehicle passage at the same time.Bund extensions are assumed to be in place, tOmwide and projecting halfway towards the tank.These extensions would provide a safe vantagepoint to place monitors during a foam attack andan escape route if necessary. In practice, the facil­ities available would probably fall well short ofthis, and additional fire brigade equipment wouldbe required to compensate.

Hydrant spacing is taken as 80m, each hydrantbeing equipped with four 70mm outlets. Tables 8.6and 8.10 show the derivation of the lengths of hoserequired.

It has been assumed that water supplies in thehydrant main are at sufficient pressure. Thehydrant main should be capable of providing thefull foam and cooling water demand at a residualpressure of not less than 2 bar to ensure a reliablesupply to the pumps.

(d) Limitations of ConventionalFire Attack

One of the main limitations of using conventionalequipment for fighting large storage tank fires isthe range and trajectory height that can be achievedby foam monitors. Methods of increasing these arediscussed in Chapter 7, Section 5 and include:

• Reducing the expansion ratio of the foam.

• Increasing the pump pressure.

• Reducing the distance from pump to moni­tor.

• Larger capacity monitors.

• Changing foam induction method.

• Elevation of monitors.

Tables 8.1 and 8.2 show that even underfavourable conditions very large quantities of con­ventional equipment are required.

The problems of fire ground organisation canbecome extreme with insufficient room to layhose, park appliances, and operate monitors. Whenthe traffic movement requirements of keepingfoam dams replenished with concentrate are addedand the number of personnel required is taken intoaccount, the logistics can become impractical attank farms where space is restricted.

This situation can itself be dangerous to thoseinvolved in a rapid retreat from, for example, aboil-over or a slop-over, or where there is a need tore-deploy firefighters and equipment due to achange in wind direction. In addition, when failureof hoses, pumps, proportioners or monitors occurs,space is required to remove the equipmentconcerned and replace it.

The organisation of resources for a major incidentinvolving a large tank fire is a very complex taskin itself. Sources of foam concentrate must beidentified and transported to the fireground,replacement fire crews, messing, first aid, andcontrol of the public are a few of the ancillaryactivities which require organi ·ation.

The conclusion that it is intended should be drawnfrom this Section is that any ways that can befound to reduce the quantities of equipmentrequired to tackle large tank fires is well worth­while.

rl TPe logistical problems and lackI ot'flexibility which would occur

fronl the use of conventional fireb_rigad~ equipment against largetank.Jiresshow that this- ', ... -.' - --;. -_. -- .. _- - -

app'roach is:'unlikel)' to succeedPHd c~~ld:(j~:·q~Dgerous to those

~; ... '''" . '- ,-

l JQYQI~~9-~:; .~.~:~..

66 Fire Service Manual

----------

Firefighting Foam 67

Table 8.1: Large Storage Tank Fires, Conventional DeploymentSummary of Foam Attack and Cooling Water Requirements

Tank Diameter (ISm high) 45m 60m 75m 90m

Water For Cooling (lpm) 13,300 20,400 27,600 36,800

Water For Foam Attack (lpm) 11,400 20,600 31,900 50,300

Total Water Usage (litres) 3,880,000 6,140,000 8,550,000 11,860,000

60 Minute Foam Attack, 4 Hours CoolingAdjacent Tank

3% Foam Concentrate (lpm) 360 640 990 1,600

Total Concentrate Usage (litres) 60 Minute 21,100 38,200 59,200 93,400

Foam Attack

Foam Solution (Ipm) 11,700 21,200 32,900 51,900

Total Foam Solution Usage (litres) 710,000 1,280,000 1,980,000 3,120,000

60 Minute Foam Attack

Foam Monitors (each 1900 Ipm) 7 12 18 28

Water Cooling Monitors (each 1900 Ipm) 7 1I 15 20

Pumps (one per monitor) 14 23 33 48

Hydrant Outlets (2 per pump) 28 46 66 96

Number of 25m Lengths of 70mm Hose 96 168 260 464

Total Length of 70mm hose (km) 2.4 4.2 6.5 11.6

Notes to Tahle 8.1:a. The water cooling rate of [he adjacent tank used for these calculations is 10.2 Ipm/m' of 1/3rd of the tank sUlface

area. This rate could be reduced to 2Ipm/m! (see Chapter 7. Section 5 b) (iii)).h. The /iJam application rates used for these calculations are [he Home Office recommended minimum application

rutes (see Chapter 4). The calculations assume J% alcohol resistant film-forming foam concentrate is being used.c. No allowance has been made for any additional foam concentrate requirements as a result of an increased foam

application rate during firefighting due 10 losses, or/iJl' continued application after extinction. Losses could add asmuch as 60% 10 these requirements with associated increases in foam attack water and equipment (see Chapter 4).

d. All numbers are approximate.

Table 8.2: Large Storage Tank Fires, Conventional DeploymentSummary of Resource Requirements For 60 Minute Foam Attack

Tank Diameter (ISm high) 45m 60m 75m 90m

Water For Foam Attack (lpm) IIAOO 20,600 31,900 50,300

3% Foam Concentrate (lpm) 360 640 990 1,600

Foam Solution (lpm) 11,700 21,200 32,900 51,900

Total Water (litres) 681,000 1,240,000 1,920,000 3,020,000

Total 3% Foam Concentrate (litres) 21,100 38,200 59,200 93,400

Total Foam Solution (litres) 710,000 1,280,000 1,980,000 3,120,000

Foam Monitors (each 1900 Ipm) 7 12 18 28

Pumps (one per monitor) 7 12 18 28

Hydrant Outlets (2 per pump) 14 24 36 56

Hydrants (4 outlets per hydrant) 4 6 9 14

Lengths of 70mm Hose (each 25m) 48 88 148 288

Notes to Table 8.2:a. The foam application rates used for these calculations are the Home Office recommended minimum application

rates (see Chapter 4). The calculations assume 3% alcnhol resistant film-forming foam concentrate is heing used.b. No allowance has been made for any additional foam cnncentrate requirements as a result of an increased jiJam

application rate during firefighting due to losses, orfor continued application after extinction. Losses could add asmuch as 60% to these requirements with associated increases in foam attack water and equipment (see Chapter 4).

c. All numbers are approximate.

Table 8.3: Large Storage Tank Fires, Conventional DeploymentFoam Solution and 3%/6% Foam Concentrate Requirements Per Minute

Tank Surface Foam Solution 3% Foam 6% FoamDiameter Area Concentrate Concentrate

of Topof Tank

(Ipm) (lpm) (lpm)

FP Film- FP Film- FP Film-(m) (m') forming forming forming

45 1,600 14,400 11,700 440 360 870 710

60 2,900 26,100 2[,200 780 640 1,600 1,300

75 4,500 40,500 32,900 1,300 990 2,400 2,000

90 6AOO 64,000 51,900 2,000 1,600 3,900 3,200

Notes 10 Table 8.3:a. The foam application rates used for these calculations are the Home Office recommended minimum application

rates (see Chapter 4).b. No allowance has been made for any additional foam concentrate orfoam solution requirements as a result ofan

increased jiJam application rate during firefighting due to losses, or for continued application after extinction.Losses could add as much as 60% to these requirements (see Chapter 4).

c. All numbers are approximate.

68 Fire Service Manual Firerighting Foam 69

Table 8.4: Large Storage Tank Fires, Conventional DeploymentTotal 3%/6% Foam Concentrate Requirements For a 60 Minute Foam Attack

Table 8.6: Large Storage Tank Fires, Conventional Deployment70mm Hose Requirements For a Foam Attack - Hydrants to Pumps

Notes to Tahle 8.4:a. The foam application rates used for these calculatiolls are the Home Office recommended minimum application

rates (see Chapter 4 J.b. No allowance has been made for any additional jiJam concentrate requirements as a result of' an increased foam

application rate during firefighting due to losses, or/or continued application after extinction. Losses could addas much as 60% to foam concentrate requirements with associated increases in foam attack water and equipment(see Chapter 4).

c. Allnumhers are approximate.

(m) (ml)

45 1,600

60 2,900

75 4,500

90 6,400

Tank Surface No. of No. of No. of Distance No. of No. of Total TotalDiameter Area Pumps Hydrant Hydrants From Hose 25m No. of Length

of Top Outlets Needed Hydrants Runs Lengths Lengths of Hoseof Tank Needed (4 outlets to Pumps for Each Required of25m

per Distance Hose(m) (m2) hydrant) (km)

45 1,600 7 14 4 2<25m 8 8 20 0.5

2<50m 6 12

60 2,900 12 24 6 2<25m 8 8 40

4<50m 16 32

75 4,450 18 36 9 2<25m 8 8 76 2.3

6<50m 24 48

1<125m 4 20

90 6,400 28 56 14 2<25 m 8 8 176 4.9

6<50m 24 48

6<125m 24 120

42,100

76,300

119,000

187,000

51,900-------

94,000--------

146,000--------

231,000

FP

6% FoamConcentrate(litres)

21,100-------

38,200--------

59,200--------

93,400

Film­forming

26,000-------

47,000--------

72,900--------

1]6,000

FP

3% FoamConcentrate(litres)

Surface Areaof Top of Tank

TankDiameter

Table 8.5: Large Storage Tank Fires, COlll'entional DeploymeJltWater Requirements For a 60 Minute Foam Attack

Tank Sluface Area Water Total Volume of WaterDiameter of Top of Tank

(Ipm) (litres)

FP Film- FP Film-(m) (m') forming forming

45 1,600 14,000 11,400 839,000 680,000

60 2,900 25,400 20,600 1,520,000 1,240,000

75 4,500 39,300 31,900 2,360,000 1,920,000

90 6,400 62,100 50,300 3,730,000 3,020,000

Notes to Table 8.6:a. 6<f25m means six hydrants are located less than 125mfrom the pump that they supply.b. No allowance has been made for any additional equipment requirements as a result of an increased foam applica­

tion rate during firefighting due to losses. or for continued application after extinction. Losses could add as muchas 60% to the foam concentrate requirements with associated increases in foam attack water and equipment (seeChapter 4).

c. All numbers are approximate.

Notes to Table 8.5 :a. The foam application rates used for these calculations are the Home Office recommended minimum application

rates (see Chapter 4).h. No allowance has heen made for any additional foam concentrate requirements as a result of an increased foam

application rate during jirefighting due to losses, orfor continued application ajier extinction. Losses could addas much as 60% to these requirements with associated increases infown attack water (see Chapter 4).

c. All numbers are approximate.

70 Fire Service Manual Firefighting Foam 7l

73Firefighting Foam

Note to Table 8. 9:a. The water cooling rate o.lthe adjaceJ1l tank used for these calculations is 10.2 lpm/m' of 1/3rd of the lank surface

area. This rate could be reduced to 2 IpmJm' (see Chapter 7, Section 5 b) (iii)) .b. All numbers are approximate.

Table 8.10: Large Storage Tank Fires, Conventional Deployment70mm Hose Requirements For Cooling ofAdjacent Tank - Hydrants to Pumps

Tank Tank No. of No of No. of Distance No. of No. of Total No. TotalDiameter Height Pumps Hydrant Hydrants From Hose 25m Lengths length

Outlets Needed Hydrants Runs Lengths of25m of HoseNeeded (4 outlets to Pumps for Each Required Hose

per hydrant) Distance(m) (m) (km)

45 15 7 14 4 2<25m 8 8 20 0.5

2<50m 6 12

45 20 8 16 4 2<25m 8 8 24 0.6

2<50m 8 16

45 25 10 20 5 2<25m 8 8 32 0.8

3<50m 12 24

60 15 11 22 6 2<25m 8 8 36 0.9

4<50m 14 28

75 15 15 30 8 2<25m 8 8 52 1.3

6<50m 22 44

90 15 20 40 10 2<25m 8 8 96 2.4

6<50m 24 48

2<125m 8 40

Notes to Table 8.10:a. 2<125m means two hydrants are located less than 125mfromthe pump that they supplyb. All numbers are approximate.

Table 8.7: Large Storage Tank Fires, Conventional Deployment 70mm Hose Requirements For a Table 8.9: Large Storage Tank Fires, Conventional DeploymentFoam Attack - Pumps to Monitors And Total For Foam Attack Cooling Water Requirements For Adjacent Tank - Calculation

Tank Surface No. of No. of Length No. of 25m Total No Total Hose. Tank Surface Tank SUIface Total 1/3 of 1/3 Tank Total WaterDiameter Area of Monitors Hose Runs of Runs Lengths of25m Length From Diameter Area Height Area of Surface Total Tank Surface For 4 hours

Top of Needed Needed Required lengths Hydrants of Top the Tank Area of SUIface Area x Cooling ofTank From to Pumps of Tank Sides Tank Area 10.2Ipm/m l Adjacent Tank

Hydrants to Monitors (m) (m') (m) (m') (m') (m') (lpm) (litres)to Pumps

45 1,600 15 2,200 3,800 1,300 13,300 3,200,000to Monitors(m) (m') (km) 45 1,600 20 2,900 4,500 1,500 15,300 3,680,000

45 1,600 7 14 <50m 28 48 1.2 45 1,600 25 3,600 5,200 1,800 18,400 4,420,000

60 2,900 12 24 <50m 48 88 2.2 60 2,900 15 2,900 5,800 2,000 20,400 4,900,000

75 4,500 18 36 <50m 72 148 3.7 75 4,500 15 3,600 8,100 2,700 27,600 6,630,000

90 6,400 28 56 <50m 112 288 7.2 90 6,400 15 4,300 10,700 3,600 36,800 8,840,000

Notes to Table 8. 7:a. <50m means less than 50 metres.b. No allowance has been made for any additional equipment requirements as a result of an increased foam applica­

tion rate during firefighting due to losses, or/or cOl1linued application after extinction. Losses could add as muchas 60% to the foam concentrate requirements with associated increases in foam allack water and equipment (Sf('

Chapter 4).c. All numbers are approximate.

Table 8.8: Large Storage Tank Fires, Conventional DeploymentSummary ofResource Requirements for the Cooling Water ofan Adjacent Tank

Diameter of Tank to be Cooled 45m 45m 45m 60m 75m 90m

Height of Tank to be Cooled 15m 20m 25m 15m 15m 15m

Water For Cooling (lpm) 13,300 15,300 18,400 20,400 27,600 36,800

Total Water Required For 4 3,200,000 3,680,000 4,420,000 4,900,000 6,630,000 8,840,000Hours Cooling (litres)

Water Monitors (each 1900 tpm) 7 9 10 II 15 20

Pumps (one per monitor) 7 9 10 11 15 20

Hydrant Outlets (2 per pump) 14 18 20 22 30 40

Hydrants (4 outlets per hydrant) 4 5 5 6 8 10

Notes to Table 8.8:a. The water cooling rate 0/ the adjaceJ1ltank used for these calculations is 10.2 Ipm/m' of 1/3rd of the tank surface

area. This rate could be reduced to 2 lpm/m? (see Chapter 7, Section 5 b) (iii)) .b. All numbers are approximate.

72 Fire Service Manual

Table 8.11: Large Storage Tank Fires, Conventional Deployment70mm Hose Requirements For Cooling ofAdjacent Tank - Pumps to Monitors and TotalRequired For Cooling

Tank Tank No. of Total No. Length of Total No. Overall Overall

Diameter Height Water of Hose Each Run of25m Total No. Total

Monitors Runs Lengths of Lengths Length of

Needed From of Hose of Hose Hose

(each 1900 Pumps to Required Required Required

Ipm) Monitors From For ForPumps to Cooling CoolingMonitors

(m) (m) (km)

45 15 7 14 average 50m 28 48 1.2

45 20 8 16 average 50m 32 56 lA

45 25 10 20 average 50m 40 72 1.8

60 15 I I 22 average 50m 44 80 2.0

75 15 15 30 average 50m 60 112 2.8

90 15 20 40 average 50m 80 176 404

Note to Table 8.11:a. All numbers are approximate.

The advantages in the use of large capacity nozzles

are:

because of internal obstructions in the boredesigned to produce improved foam work­ing.

• Technical information on some of the moni­tors is sparse, particularly regarding range,trajectory, foam ground pattern, feathering(fallout from the stream) etc.

(c) Large Pumps

Larger sized pumps, such as those on 4,500 litreper minute pumping appliances or skid mountedpumps of similar or larger capacity, have manyadvantages. These include a reduction in the

Nozzle Flow Max. Foam Expansion Ratio/ Foam TypePressure ([pm) Horiz. Coverage(bar) Range at Landing

(metre) Point

7 8,000 80 4-6: I / AFFF-AR

7 16,000 90

8 18,000 100

8 23,000 100 18m x 36m

8 23,000 95 4-6: I / AFFF-AR

8 30,000 110

9 38,000 135 21m x 46m

7-8 15,000 100 4-6: I / AFFF-AR

23,000 107

30,000 110 20m x 40m

38,000 119 21m x 46m

45,000 122 55m x 24m

53,000 131

6 75 5-6: 1/ FP

8 15,000 85

10 95

6 90 FP8 40,000 110

10 47,800 125

Notes to Table 8.12:The information given in this table has been provided by manufacturers. Distances givenare for foam throw in wind free conditions and at different elevations.

D

A

Table 8.12: Large capacity LXfoam nozzles: performance data

c

Nozzle

E

B

The disadvantages are:

• Some of them, especially the very largecapacity nozzles, can only be used for veryfew specialised tasks i.e. fighting large tankfires.

• There is a high cost involved in both buyingthis equipment and training firefighters touse it.

• They are heavy and difficult to manoeuvre,although the larger ones are mounted onpurpose designed trailers or on appliances.

• Some large monitor designs have shorterranges than would be expected, primarily

They have been claimed to have been usedsuccessfully against large tank fires.

Smaller numbers of monitors are required.

They can be readily used with large diame­

ter hose.

The localised application of a large quantityof finished foam when using larger monitorsmakes it easier to achieve a "bite" on the firethan when using smaller monitors.

Larger nozzles have a longer range thansmaller nozzles when used at the same oper­

ating pressure.

The larger jets are more resilient to the heatand updraft effects involved when penetrat­ing the fire plume of a burning storage tank.

•••

•

•

•

(b) Large Nozzles

Several large capacity nozzles are available. Theserange in capacity with the biggest in the order of50,000 litres of foam solution per minute. Table8.12 provides some manufacturers pelformanceinformation for these larger nozzles.

This Section looks at some of the specialist equip­ment and facilities that can be used to tackle largescale tank fires. Their use would reduce many ofthe problems highlighted in the previous Sectionconcerning the use of conventional fire serviceequipment to tackle these fires. However, beforemodifying facilities and employing such equip­ment, there is a need for thorough assessments tobe made in order to quantify advantages and dis­advantages and to evaluate the performance char­acteristics of equipment in realistic operating con­

ditions.

(a) General

8.3 Technical Option.

74 Fire Service Manual Firefighting Foam 75

number of crews required for a foam attack,reducing the amount of space required for appli­ances, and reducing the logistical complexitiesdiscussed above. Pump sizes could be selected tomatch the capacity of the supply requirements ofsome of the smaller monitors (e.g. one pump permonitor or one pump per two monitors). Suchpumps would provide the opportunity to use largesizes of suction hose, as well as large deliveryhose.

The obvious disadvantages of using larger pumpsare similar to those of using large monitors andinclude in particular cost, specialist use and addi­tional training requirements.

Vehicle mounted or trailer mounted pumps withcapacities in excess of 23,000 litres per minute areavailable.

(d) Large Hose

Use of large diameter hose is considered vital toenable control and flexibility on the fireground.One 150mm diameter suction hose and one150mm diameter discharge hose is more than suf­ficient to supply a single 3,800 litre per minutemonitor, compared with four 70mm hoses. Inaddition, hose laying vehicles should be consid­ered to rapidly deploy and retrieve hose lengths.Where long runs of hose are required, as maywell be the case with storage tank fires, the timesaved in deployment by such a vehicle, at speedsof up to 30 mph if necessary, can be of crucialimportance.

Where possible, large diameter suction hoseshould be connected directly, or via a junctioncoupling, into the large diameter outlet at a sitehydrant. Where these do not exist, 4 to I adapterheads (sometimes referred to as phantom pumpercollecting breechings) can be fabricated to enable70mm outlets to be coupled to 150mm suctionhose.

150mm diameter lay flat delivery hose is widelyavailable and sizes in excess of 250mm are in pro­duction for specialist applications. It should beremembered that the couplings are the most expen­sive part of large diameter hoses and so hoselengths should be chosen with care.

(e) Bund Architecture

Typical storage tank bunds in the UK consist of 3mhigh sloping sided earth banks. Access to andaround storage tank bunds is often by means of a3-4m wide road near to the outer base of the bundwall. Little or no provision is generally made forvehicle marshalling or hose runs. The followingare suggestions for features of designs which couldbe considered for new constructions or refurbish­ment of existing facilities:

• Marshalling points for fire appliances.

• 10m wide road ways to allow hose runs andvehicles to pass.

• Bund extension piers. Where it is difficult toproject foam over tank walls from the sur­rounding bund wall, such extensions wouldprovide a suitable platform for monitors byreducing the range and increasing the eleva­tion above the bund floor. In addition, thereis a considerable degree of safety for fire­fighters in being able to tend and train mon­itors outside of the bunded area. In the eventof a boil-over, froth-over or slop-over theirelevation would provide additional time toeffect an escape, and they would be on apaved exit route where vehicles could bereadily used.

• Concrete faced bund walls to prevent ero­sion by weather and by water from bursthoses etc. Special care should be taken inbund maintenance to ensure no points ofweakness develop (for example aroundpipework that penetrates the bund walls).When a bund is full of liquid, any leakagecan lead to rapid erosion and loss of con­tainment.

• For liquefied gases, lower diversion wallscan be provided within the main bund tochannel small spills to a catchment pit awayfrom the tank and close to the main bundwall for ease of extinguishment.

• Facilities for drainage of bunds should beprovided under the control of an isolationvalve.

)

(0 Fixed Equipment

The role of fixed fire protection is of great impor­tance in minimising the extent of manual firefight­ing required. For floating roof tanks, top pourersare usually designed for rim seal protection onlyand are likely to be damaged in fully involved tankfires. Similarly, with fixed roof tanks, top pourersare often damaged during the ignition phase.

Subsurface injection systems are not normallydamaged during tank fires. These can be particu­larly useful for fixed roof tank fires where there isno obstruction in the form of a sunken roof struc­ture. However. the extent of spread from sub-sur­face injection is limited, probably to less than 30min anyone direction, so for larger tanks, over-the­top application is still essential to achieve extin­guishment. The use of both base injection systemsand over-the-top application can be the most effec­tive combination available for large tank fires.

In determining the requirements of equipment andmaterials for manual firefighting. no account shouldbe taken of fixed protection since it can be out ofservice when required and cannot be regarded as acommon protection feature on storage tanks.

For tanks over 45m diameter, which present a con­siderable challenge to any manual system of foamapplication, it is recommended that fixed baseinjection systems should be provided.

(g) Elevated Equipment

By elevating monitors it may be possible to directthe foam to the required point on the fuel surfacewhich could be particularly useful as a method ofassisting the foam to flow the whole way acrossthe burning fuel in a tank by:

• Advancing the foam landing zone as thefoam front progresses.

• Directing the foam stream at the foam blan­ket near the side of the tank to encourage acircular movement.

Foam delivery equipment can be elevated by:

• Purpose made foam towers.

• Mounting the monitor/nozzle on an elevat­ing platform.

• Fixing the monitor/nozzle to the jib of acrane.

Care must be taken in the case of the elevatingplatform as the jet reaction may affect the stabilityof the unit.

In all methods of elevating equipment. somemethod of remote control would be a distinctadvantage.

(h) Implications of Use of SpecialistEquipment

Tables 8.13 to 8.19 show the development of thelogistics of firefighting with specialist equipmentin direct comparison to the use of conventionalequipment.

There is no immediately obvious saving in thequantities of water or concentrate required but thepercentage savings in foam equipment comparedwith conventional deployment are as follows:

3,8001pm 7,6001pm 15,0001pmMonitors Monitors Monitorsand Pumps and Pumps and Pumps

Monitors 43-50% 71-75% 82-86%

Pumps 43-50% 71-75% 82-86%

Hoselengths 71-75% 87-91% 83-90%

In addition. the transportation of foam concentratecan be greatly simplified by the use of far fewerlarge foam concentrate containers (i.e. foam dams,foam tankers, bulk containers etc.).

The numbers of firefighters involved directly inthe foam attack can be reduced along with thereduction in equipment, with a correspondinglower requirement for standby crews and logisticsupport. It is far easier to re-deploy the foamattack when needed since less items of equipmentneed to be moved. There is also a better chance of

76 Fire Service Manual Firejighting Foam 77

extinguishing the fire when using specialist equip­ment because deployment can be achieved earlierand because large nozzles should be more effec­tive in penetrating the fire plume and getting a"bite" on the fire.

Although not illustrated here, the application ofcooling water can also be simplified by the use oflarge suction hose, large pumps and large deliveryhose to distribution headers. However, smallerwater monitors, such as those with a 1,900 litre perminute capacity, would still be useful for coolingbecause a smaller number of larger monitors maydistribute the water less evenly, and there are notthe same problems with monitor range when pro­jecting water.

It can be expected that the use of specialist equip­ment would increase the sizes of storage tank firesthat could be successfully tackled and extin­guished. For fires in tanks of less than 45m, itwould greatly simplify the logistics and theprocess of extinguishment. For larger storagetanks, it may be possible to extinguish fires that arebeyond the capabilities of present equipment.

Table 8.13: Large Storage Tank Fires, Specialist Equipment Deployment-Summary of Resource Requirements For 60 minute Foam Attack

Tank Diameter (l5m high) 45m 60m 75m 90m

Water For Foam Attack (Ipm) 11,400 20,600 31,900 50,300

3% Foam Concentrate (Ipm) 360 640 990 1,600

Foam Solution (Ipm) 11,700 21,200 32,900 51,900

Total Water (litres) 681,000 1,240,000 1,920,000 3,020,000

Total 3% Foam Concentrate (litres) 21,100 38,200 59,200 93,400

Total Foam Solution (litres) 710,000 1,280,000 1,980,000 3,120,000

Foam Monitors (each 1,900 Ipm) 7 12 18 28

Pumps (one per monitor) 7 12 18 28

Hydrant Outlets (2 per pump) 14 24 36 56

Hydrants (4 outlets per hydrant) 4 6 9 14

Lengths of 70mm Hose (each 25m) 48 88 148 288

Foam Monitors (each 3,800 Ipm) 4 6 9 14

Pumps (3,800 Ipm, one per monitor) 4 6 9 14

Hydrant Outlets (I x 150mm per pump) 4 6 9 14

Hydrants (each I x 150mm outlet) 4 6 9 14

Lengths of 150mm Hose (each 25m) 14 22 37 72

Foam Monitors (each 7,600 Ipm) 2 3 5 7

Pumps (7,600 Ipm, one per monitor) 2 3 5 7

Hydrant Outlets (I x 150mm per pump) 2 3 5 7

Hydrants (each I x 150mm outlet) 2 3 5 7

Lengths of 150mm Hose (each 25m) 6 10 18 26

Foam Monitors (each 15,000 Ipm) 2 3 4

Pumps (15,000 Ipm, one per monitor) 2 3 4

Hydrant Outlets (2 x 150mm per pump) 2 4 6 8

Hydrants (each I x 150mm outlet) 2 4 6 8

Lengths of 150mm Hose (each 25m) 6 14 22 30

Notes to Table 8. J3:a. Thefoam application rates used for these calculations are the Home Office recommended minimum application

rates (see Chapter 4).b. No allowance has been made for any additional foam concentrate requireme/1/s as a result of an increased foam

application rate during firefighting due to losses, or for continued application after extinction. Losses could addas much as 60% to the foam concentrate requirements with associated increases in foam attack water and equip­ment (see Chapter 4).

c. All numbers are approximate.

78 Fire Service Manual Firejighting Foam 79 r-----------------------------------------------_........_---------------------------------------------------

Table 8.14: Large Storage Tank Fires, Specialist Equipment Deployment - lS0mm HoseRequirements For a Foam Attack - Hydrants to Pumps, Pumps and Monitors 3,800 lpm

Table 8.15: Large Storage Tank Fires, Specialist Equipment Deployment -150mm Hose Requirements For aFoam Attack - Pumps to Monitors, Pumps and Monitors 3,800 lpm

Tank SUlface No. of No. of No. of Distance No. of No. of Total No. Total Tank Surface No. of No. of Length No. of Total No. Total HoseDiameter Area of Foam Hydrant Hydrants From Hose 25m Hose of Length Diameter Area of Monitors Hose of Runs 25m Hose of25m Length

Top of Monitors/ Outlets Needed Hydrants Runs Lengths Lengths of Hose Top of Needed Runs Lengths lengths FromTank Pumps Needed (1 outlet to Pumps for Each Required of Tank (each Needed Required From Hydrants

Needed per Distance (150mm 25m Hose 3,800 (l50mm Hydrants to Pumps(each hydrant) Diameter) Ipm) Diameter) to Pumps to Monitors3,800 to MonitorsIpm) (m) (m2) (km)

(m) (m2) (km)45 1,600 4 4 <50m 8 14 0.4

45 1,600 4 4 4 2<25m 2 2 6 0.21260 2,900 6 6 <50m 22 0.6

2<50m 2 49 <50m 1875 4,500 9 37 1.0

60 2,900 6 6 6 2<25m 2 2 10 0.32890 6,400 14 14 <50m 72 1.8

4<50m 4 8

75 4,500 9 9 9 2<25m 2 2 19 0.5Notes to Tahle 8.15:

6<50m 6 12<50m means less than 50 metres.a.

1<125m 5 b. No allowance has been made for any additionalf(Jam concentrate requirements as a result of an increased foam

90 6,400 14 14 14 2<25 m 2 2 44 1.1application rate during firefighting due to losses, or/or continued application after extinction. Losses could addas much as 60% to the foam concentrate requirements lvith associated increases in foam attack water and equip-

6<50m 6 12 ment (see Chapter 4).c. All numbers are approximate.

6<J25m 6 30

Notes to Table 8.14:

a. The number of monitors required has been calculated hy dividing the foam solution rate requirement for film­forming foam (see Table 8.13) by the capacity of the foam monitors (3,800 Ipm)

b. 6< 125m means six hvdrants are located less than 125m from the pump that they supply.C'. No allowance has been made for any additional foam concentrate requirements as a result of an increased foam

application rate during firefighting due to losses. or for continued application afier extinction. Losses could addas much as 60% to the foam concentrate requiremellls with associated increases in foam attack water ((nd equip­ment (see Chapter 4).

d. All numbers are approximate.

80 Fire Service Manual Firefighting Foam 81

Table 8.17: Large Storage Tank Fires, Specialist Equipment Deployment -150mm HoseRequirements For a Foam Attack - Pumps to Monitors, Pumps and Monitors 7,600 lpm

(m) (m2)

45 1,600 2 2 <50m

60 2,900 3 3 <50m

75 4,500 5 5 <50m

90 6,400 7 7 <50m

Notes to Tahle 8./7:

<50m means less than 50 metres.

No allowance has heen made for any additional foam concentrate requirements as a result of an increased foamapplication rate during jirejighting due to losses, or for continued application after extinction. Losses could addas much as 60% to the foam concentrate requirements with associated increases in foam attack water and equip­ment (see Chapter 4).All numhers are approXimate.

Table 8.16: Large Storage Tank Fires, Specialist Equipment Deployment - 150mm HoseRequirements For a Foam Attack - Hydrants to Pumps, Pumps and Monitors 7,600 lpm

Tank Surface No. of No. of No. of Distance No. of No. of Total No. TotalDiameter Area of Foam Hydrant Hydrants From Hose 25m Hose of Length

Top of Monitors Outlets Needed Hydrants Runs Lengths Lengths of HoseTank fPumps Needed (I outlet to Pumps for Required of25m

Needed per Each ( 150mm Hose(each hydrant) Distance Diameter)7,600Ipm)

(m) (m2) (km)

45 1,600 2 2 2 2<25m 2 2 2 0.1

60 2,900 3 3 3 2<25m 2 2 4 0.1

1<50m 2

75 4,500 5 5 5 2<25m 2 2 8 0.2

3<50m 3 6

90 6,400 7 7 7 2<25 m 2 2 12 0.3

5<50m 5 10

Notes to Table 8./6:

a. The number of monitors required has been calculated by dividing the foam solution rate requirement for film­forming foam (see Table 8.13) by the capacity of the foam monitors (7,600 Ipm)

h. 2<25m means two hydrants are located less than 25mfiwI1 the pump that they supply.c. No allowance has heen made for any additional foam concentrate requirements as a result of an increased

foam application rate during firefighting due to losses, orfor continued application after extinction. Lossescould add as much as 60% to the foam concentrate requirements with associated increases in foam attackwater and equipment (see Chapter 4).

d. All numbers are approximate.

•

TankDiameter

a.h.

c.

SurfaceArea ofTop ofTank

No. ofMonitorsNeeded(each7,600Ipm)

No. ofHose RunsNeeded

Lengthof Runs

No. of Total No. Total Hose25m Hose of25m LengthLengths lengths FromRequired From Hydrants(150mm Hydrants to PumpsDiameter) to Pumps to Monitors

to Monitors(km)

4 6 0.2

6 10 0.3

10 18 0.5

14 26 0.7

82 Fire Service Manual Firejighting Foam 83

Table 8.18: Large Storage Tank Fires, Specialist Equipment Deployment -150mm Hose Table 8.19: Large Storage Tank Fires, Specialist Equipment Deployment - 150mm HoseRequirements For a Foam Attack - Hydrants to Pumps, Pumps and Monitors 15,000 lpm Requirements For a Foam Attack - Pumps to Monitors, Pumps and Monitors 15,000 lpm

Tank Surface No. of No. of No. of Distance No. of No. of Total No. Total Tank Surface No. of No. of Length No. of Total No. Total HoseDiameter Area of Foam Hydrant Hydrants From Hose 25m Hose of Length Diameter Area of Monitors Hose of Runs 25m Hose of25m Length

Top of Monitors Outlets Needed Hydrants Runs Lengths Lengths of Hose Top of Needed Runs Lengths lengths FromTank fPumps Needed (I outlet to Pumps for Each Required of25m Tank (each Needed Required From Hydrants

Needed per Distance (150mm Hose 15,000 (l50mm Hydrants to Pumps(each hydrant) Diameter) Ipm) Diameter) to Pumps to Monitors15,000 to MonitorsIpm) (m) (m2

) (km)(m) (m2) (km)

45 1,600 2 <50m 4 6 0.245 1,600 2 2 2<25m 2 2 2 0.1

60 2,900 2 4 <50m 8 14 0.460 2,900 2 4 4 2<25m 2 2 6 0.2 75 4,500 3 6 <50m 12 22 0.6

2<50m 2 490 6,400 4 8 <50m 16 30 0.8

75 4,500 3 6 6 2<25m 2 2 10 0.3

4<50m 4 8 Notes to Table 8./9a. <50m means less than 50 metres.

90 6,400 4 8 8 2<25 m 2 2 14 0.4 h. No allowance has been made for an." additional foam cOllcelltrate requirements as a resu.lt of an increased

6<50m 6 12 foam application rate during firefighting due to losses, or for continued application after extinction. Lossescould add as much as 60% to thefoam concentrate requirements with associated increases in foam auackwater and equipment (see Chapter 4).

Notes to Table 8./8: c. AI/numbers are approximate.

a. The lIumber of monitors required has been calculated br dividing the foam solution rate requirement for film­forming foam (see Table 8./3) by the capacity of the foam monitors (/5,000 Ipm)

b. 4<50m means four hydrants are located less than 50m from the pump that they supply.c. No allowance has been made fur an." additional foam concentrate requirements as a result of an increased

foam application rate during firefighting due to losses, orfor continued application afier extinction. Lossescould add as much as 60% to the foam concentrate requirements with associated increases in foam auackwater and equipment (see Chapter 4).

d. All numbers are approximate.

84 Fire Service Manual

.,

Firefighting Foam 85

F-refighting Foam

References Further Reading

I.

2.

3.

4.

CFBAC, JCFR Report 19, Trials ofMedium and High Expansion Foams onPetrol Fires, P L Parsons, 1982.

FROG Publication 3/91, Additives forHosereel Systems: Trials of Foam onWooden Crib Fires, B P Johnson, 1991.

CFBAC, JCFR Report 49, The Use ofFoam Against Large-Scale Petroleum FiresInvolving Lead-Free Petrol SummaryReport, J A Foster, 1992.

CFBAC, JCFR Report 31, Additives forHosereel Systems Trials of Foams 011 40m2

Petrol Fires, J A Foster, 1988.

I.

2.

3.

CFBAC, JCFR Report 40, Survey ofFirefighting Foams, Associated Equipmentand Tactics [Ewbank Preece Reports] 1990.ISBN 0 82652 556 X

Part I : Firefighting FoamsPart 2 : Tactics and EquipmentPart 3 : Large Tank Fires

Fire Service Manual - Volume 2 - FireService Operations - Petrochemicals.

Fire Service Manual - Volume 1 - FireService Technology, Equipment andMedia - Foam.

5. SROB Publication 10/87, Test of TwoCompact High Expansion FoamGenerators Produced by SymtolEngineering Lld in 1982, J A Foster,B P Johnson, 1988.

6. CFBAC, JCFR Report 24, Trials andMethods of Foam Disposal Following Useof High Expansion Foam, FE Smith, 1985.

Firejighting Foam 87 ~

----------------------------------------------~.---- ------------------ J!I

Firefighting Foam

Glossary of Terms: Firefighting Foams

(Note: Not all of these terms have been used in this Manual of Firemanshipbut they have been included here for completeness)

Accelerated ageing

Acidity

Alcohol resistantfoam concentrates

Alkalinity

Application rate

AFFF concentrate

Aspiration

Aspirated foam

Base injection(Subsurface injection)

Bite

Storage of foam concentrate at high temperatures to indicatelong term storage properties of the foam concentrate at ambienttemperatures.

See pH.

These may be suitable for use on hydrocarbon fuels, andadditionally are resistant to breakdown when applied to thesurface of water-miscible liquid fuels. Some alcohol resistantfoam concentrates may precipitate a polymeric membrane onthe surface of water-miscible liquid fuels.

See pH.

The rate at which a foam solution is applied to a fire.Usually expressed as litres of foam solution per square metre ofthe fire surface area per minute (Ipm/m2).

Aqueous film-forming foam. AFFFs are generally based on mix­tures of hydrocarbon and fluorinated surface active agents andhave the ability to form an aqueous film on the surface of somehydrocarbon fuels.

The addition or entrainment of air into foam solution.

Foam that is made when foam solution is passed through purposedesigned foam-making equipment, such as a foam-makingbranch. These mix in air (aspirate) and then agitate the mixturesufficiently to produce finished foam. (see also primary aspiratedfoam and secondary aspirated foam).

The introduction of fuel-tolerant primary aspirated finished foambeneath the surface of certain flammable and combustiblehydrocarbons, to effect fire extinguishment. Usually used forthe protection of fixed roof hydrocarbon fuel storage tanks.

The formation of an initial area of foam blanket on the surface ofa burning liquid fuel.

Firefighting Foam 89

Boiling liquidexpanding vapourexplosion (BLEVE)

Boil-over

Bund area (Dike area)

Branch

Burnback resistance

Candling

Chemical foam

Classes of Fi re

The catastrophic failure of a tank containing pressure liquefiedgas (PLG) due to mechanical damage or adverse heat exposurewill result in a BLEVE. A BLEVE will produce blast andprojectile hazards. If the contents of the tank are toxic, thenhealth and exposure hazards may occur. If the contents areflammable, then a fireball may occur with associated thermalradiation and fire engulfment hazards.

Violent ejection of flammable liquid from its container, causedby vaporisation of a water layer beneath the body of the liquid. Itwill generally only occur after a lengthy burning period in wideflashpoint range products, such as crude oil. The water layer mayalready have been in the container before the fire began or maybe the result of the inadvertent application of water (perhaps dur­ing cooling of the container walls), or from the drainage of foamsolution from finished foam applied to the fire. (see also froth­over and slop-over).

An area surrounding a storage tank which is designed to containthe liquid product in the event of a tank rupture.

A hand-held foam maker and nozzle.

The ability of a foam blanket to resist direct flame andheat impingement.

Refers to the thin intermittent flames that can move over thesurface of a foam blanket even after the main liquid fuel fire hasbeen extinguished.

A finished foam produced by mixing two or more chemicals.The bubbles are typically caused by carbon dioxide released bythe reaction.

In the UK the standard classification of fire types is definedin BS EN 2: 1992 as follows:

'Class A: fires involving solid materials, usually of anorganic nature, in which combustion normally takes placewith the formation of glowing embers.

~ I

Concentration

Critical applicationrate

Crude oil

Density

Dike area

Discharge rate(high expansion foam)

Drainage time

Expansion ratio

To achieve effective pelformance, foam concentrates must bemixed to the concentration recommended by the manufacturer.For each 100 litres of the required foam solution, the foamconcentrate must be mixed as follows:

Recommended Volume of Foam Volume of Volume ofConcentration Concentrate Water Foam Solution

(litres) (litres) (litres)

1% 99 100

3% 3 97 100

6% 6 94 lOO

The foam application rate below which a fire cannot beextinguished.

Petroleum, in its natural state, as extracted from the earth.Consequently, there are many different types of crude oil, eachwith different characteristics and each yielding different qualityproducts. The various constituents ensure that crude oils general­ly have wide ranging flash points with usually sufficient fractions(or light ends) to classify them as class A petroleum products.

The mass per unit volume of a material:

. massDenSity = --1-­

vo ume

See Bund area.

The discharge rate of a high expansion foam generator measuredin cubic metres/min (m3/min) of foam at a stated expansion ratio.

The time taken for a percentage of the liquid content of afinished foam sample of a stated depth to drain out of the foam.For low expansion foam, times taken for 25% of the foamsolution to drain out are usually given; for medium and highexpansion foams 50% drainage times are usually given.

The ratio of the total volume of finished foam to the volume offoam solution used to produce it:

Electrical fires are not included in this system of classification.

Class B:

Class C:

Class D:

fires involving liquids or liquefiable solids.

fires involving gases.

fires involving metals.'Film-forming

Expansion ratio = volume of finished foamvolume of foam solution used to produce it

A finished foam, foam solution or foam concentrate that forms aspreading, thin, aqueous film on the surface of some hydrocarbonliquids.

Cloud point

Combustible liquid

The lowest temperature at which a liquid remains clear.Usually only applicable to high expansion foam concentrates.

Any liquid having a flashpoint at or above 37.8°C (100°F).

FFFP foam concentrates Film-forming fluoroprotein. These are fluoroprotein foamconcentrates which have the ability to form an aqueous film onthe surface of some hydrocarbon fuels.

90 Fire Service Manual Firefighting Foam 91

Flow requirement (Iow The nominal supply rate of foam solution required by a foamand medium expansion) branch, measured in litres per minute.

Finished foam

Flammable liquid

Flashback

Flashpoint

Fluoroprotein (FP)foam concentrate

Foam

Foam concentrate

Foam, dry

Foam generator(high expansion)

Foam generator(Iow expansion)

Foam-making branch(foam-makingbranchpipe, FMB)

Foam monitor

Foam solution

Foam, wet

The foam as applied to the fire. It will consist of a mixture offoam solution that has been mixed with air. The foam may beprimary aspirated or secondary aspirated.

Any liquid having a flashpoint below 37.8°C (100°F).

The re-ignition of a flammable liquid caused by the exposure ofits vapour to a source of ignition such as a hot metal surface or aspark.

The lowest temperature at which a flame can propagate in thevapour above a liquid.

A hydrolysed protein based foam concentrate with addedfluorinated surface active agents.

The result of mixing foam concentrates, water and air to producebubbles.

The foam as supplied by the manufacturer in liquid form; this issometimes referred to as 'foam compound', 'foam liquid' or bytrade or brand names.

Foam with a long drainage time, i.e. the liquid content of thefoam takes a long period of time to drain out of the foam; thefoam is very stable.

A mechanical device in which foam solution is sprayed onto anet screen through which air is being forced by a fan.

Similar to a foam-making branch, but inserted in a line of hoseso that the finished foam passes along the hose to a dischargenozzle.

The equipment by which the foam solution is normally mixedwith air and delivered to the fire as a finished foam.

A larger version of a foam-making branch which cannot behand-held.

A well mixed solution of foam concentrate in water at theappropriate concentration.

Foam with a short drainage time, i.e. the liquid content of thefoam takes a short period of time to drain out of the foam; thefoam breaks down quickly.

Freeze point

Froth-over

Hazmat

Heat resistance

High expansionfoam (HX)

Hydrocarbon fuel

Induction

Inductor (Eductor)

Induction rate(pick-up rate)

Inline inductor

Knockdown

Low expansionfoam (LX)

Mechanical foam

Medium expansionfoam (MX)

Minimum usetemperature

Monitor

The highest temperature at which a material can exist as a solid.

Overflow of a non-burning flammable liquid from a containerdue to the thermal expansion of the liquid or violent boilingon top of and within the upper layers of the liquid due to thepresence of small quantities of water. (see also boil-over andslop-over)

A proprietary trade name used to describe special types of foamwhich can be used to suppress the vapour production of certainhazardous materials (toxic, odorous and/or flammable).

The ability of a foam blanket to withstand the effects of exposureto heat.

Finished foam of expansion ratio greater than 200: I

Fuels based exclusively on chains or rings of linked hydrogen andcarbon atoms. Hydrocarbon fuels are not miscible with water.

The entrainment of foam concentrate into the water stream.

A device used to introduce foam concentrate into a water line.

The percentage at which foam concentrate is proportioned in towater by an inductor in order to produce a foam solution.Normally this is 1%, 3% or 6%.

An inductor inserted in to a hose line in order to induce foamconcentrate prior to the water reaching the foam-making branch.

The ability of a foam to quickly control flames. Knockdown doesnot necessarily mean extinguishment.

Finished foam of expansion ratio of less than or equal to 20: I.

Foam produced by a physical agitation of a mixture of water,foam concentrate and air.

Finished foam of expansion ratio greater than 20: 1. but less thanor equal to 200: I.

The lowest temperature at which the foam concentrate can beused at the correct concentration through conventional equipmentsuch as inline inductors and other proportioning devices.

A large throughput branch (water or foam-making) which isnormally mounted on a vehicle, trailer or on a fixed or portablepedestal.

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Multipurpose foamconcentrates

Newtonianliquids

Non-aspirated(Unaspirated)

Non·Newtonianpseudo-plasticliquids

Oleophobic

Over-the-top foamapplication

pH (Acidity/Alkalinity)

Polar solvent

Pour point

Another name given to alcohol resistant foam concentrates.

The viscosity of Newtonian liquids remains the same no matterhow quickly or slowly they are flowing (see also non-Newtonianpseudo-plastic liquids). Most non-alcohol resistant foamconcentrates (such as AFFF, FFFP, FP, P and SYNDET) areNewtonian liquids.

The application, by any appropriate means, of a firefightingliquid that does not mix the liquid with air to produce foam(i.e. aspiration does not occur). The term 'non-aspirated foam' isoften used incorrectly to describe the product of a foam solutionthat has been passed through equipment that has not beenspecifically designed to produce foam, such as a water branch.However, the use of this type of equipment will often result insome aspiration of a foam solution. This is because air is usuallyentrained into a jet or spray of foam solution as it leaves thebranch, as it travels through the air due to the turbulenceproduced by the stream and/or when it strikes an object. Thiscauses further turbulence and air mixing. There is sufficient airentrained by these processes to produce a foam of very lowexpansion (often with an expansion ratio of less than 5: I).Consequently, the term secondary aspirated foam is preferred inthese cases (see also primary aspirated and secondary aspiratedfoam).

As the rate of flow of non-Newtonian pseudo-plastic liquidsincreases, their viscosity decreases and so they flow more easily.Consequently, getting them to flow initially can be difficult, butonce flowing, their viscosity reduces to a more acceptable level.Many alcohol resistant foam concentrates (such as AFFF-AR andFFFP-AR) are considered to be non-Newtonian pseudo-plasticliquids.

Oil repellent.

The application of foam by projecting it over the sides of astorage tank and directly on to the surface of the contained fuel.

Measurement of the acidity to alkalinity of a liquid on a scale ofI to 14. A pH of 7 is neutral (like that of pure water), a pH of I isvery acidic, a pH of 14 is very alkaline.

This term is generally used to describe any liquid which destroysstandard foams, although it actually refers to liquids whose mole­cules possess a permanent dielectric discharge e.g. Alcohols,ketones. Most polar solvents are water-miscible.

The lowest temperature at which a foam concentrate is fluid enoughto pour. This is generally a few degrees above its freezing point.

Preburn time

Premix solution

Primary aspiratedfoam

Proportioner

Protein (P) foamconcentrate

Relative density

Secondary aspiratedfoam

Security

Shear strength

Slop-over

Solution transit time

Specific gravity

The time between ignition of a fire and the commencement offoam application.

A mixture in correct proportions of a foam concentrate and water.Use of this term generally implies that the foam is stored in apremix form, as in a portable foam fire extinguisher or as foamsolution in a fire appliance water tank.

Finished foam produced from foam solutions that are passedthrough purpose designed foam-making equipment.(See secondary aspirated foam).

A device where foam concentrate and water are mixed to form afoam solution.

Protein foam concentrate contains organic concentrates derivedfrom natural vegetable or animal sources. Hydrolysed products ofprotein provide exceptionally stable and heat resistant propertiesto foams although they lack fuel tolerance and have slow knock­down performance.

see Specific gravity

Finished foams that are produced from foam solutions that areapplied other than by purpose designed foam-making equipment,usually standard water devices. (See primary aspirated foam).

The ability of a foam to seal around hot objects and preventreignition.

The measurement of the stiffness of a finished foam samplewhen measured with a foam viscometer. Units of measurementare Newtons per square metre (n1m 2).

When some burning liquids, such as heavy fuel oils or crude oils,become extremely hot, any applied water may begin to boil oncontact with the fuel, the resulting rapid expansion as it convertsto steam may cause burning fuel to overflow its containment andthe fire to spread (see also boil-over and froth-over).

The time taken for foam solution to pass from the point wherefoam concentrate is introduced in to the water stream to whenfinished foam is produced.

The specific gravity of a material is a measure of the density ofthe material in relation to the density of water. The specificgravity is calculated as:-

Specific Gravity = Density of materialDensity of water

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Water-immiscible liquid A liquid that is not soluble in water.

Spill fire

Stability

Subsurface injection

Surface active agents

Synthetic detergent(SYNDET) foamconcentrate

Venturi

Viscosity

A liquid with a specific gravity of less than one will float onwater (unless it is water-miscible); a specific gravity of morethan one indicates that water will float on top of the liquid.

A flammable liquid fire having an average depth of not morethan 25mm.

The ability of a finished foam to retain shape and form particu­larly in the presence of heat, flame and/or other liquids. The 25%drainage time is often used as a measure for stability.

See base injection.

A chemical ingredient of some foam concentrates. Finishedfoams is stabilised by the addition of surface active agents (orsurfactants) which promote air/water stability by reducing theliquids surface tension. Most surface active agents are organicin nature and common examples are soaps and detergents.

These are based upon mixtures of hydrocarbon surface activeagents and may contain fluorinated surface active agents withadditional stabilisers. They are multipurpose foams in that theycan be used at low, medium and high expansion.

A constricted portion of a pipe or tube which will increase watervelocity, thus momentarily reducing its pressure. It is in thisreduced pressure that foam concentrate is introduced. Thepressure difference across the venturi can be used to force foamconcentrate into the water.

This is a measure of how well a Iiquid will flow. Liquids aregenerally classed as either being non-Newtonian or Newtonian.A low viscosity is often desirable because it improves the flowcharacteristics of a foam concentrate through pick-up tubes,pipework and induction equipment.

Viscosity will also vary with foam concentrate type and withconcentration. AFFF foam concentrates at 3% and 6%oncentrations tend to be the least viscous, closely followed byP, FP and FFFP foam concentrates at 6%. AFFF at I% andSYNDET foams, P, FP and FFFP foam concentrates at 3%concentration are appreciably more viscous than these. Thealcohol resistant foams are often the most viscous althoughrecent developments have dramatically reduced the viscosityof some products.

In addition, the viscosity of all foam concentrates will varywith temperature and may be affected by the age of the foamconcentrate. Manufacturers often state the viscosity of theirproducts when measured at 20oC; lower temperatures will resultin higher viscosity.

Water-miscible liquid

Wetting agent

A liquid that is soluble in water. Polar solvents and hydrocarbonliquids that are water-miscible can dissolve normal firefightingfoams (see also alcohol resistant foam concentrates).

A chemical compound which, when added to water in correctproportions, materially reduces its surface tension, increases itspenetrating and spreading abilities and may also provide foamingcharacteristics.

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