AS 2430.11987

Australian Standard

Classification of hazardous areas

Part 1: Explosive gas atmospheres

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This Australian standard was prepared by Committee MS/11, Classification ofHazardous Areas. It was approved on behalf of the Council of the StandardsAssociation of Australia on 9 December 1986 and published on 2 February 1987.

The following interests are represented on Committee MS/11:Australian Electrical and Electronic Manufacturers AssociationAustralian Gas AssociationAustralian Institute of PetroleumAustralian Liquefied Petroleum Gas AssociationConfederation of Australian IndustryDepartment of DefenceDepartment of Labour, Vic.Department of Industrial Relations, N.S.W.Department of Mines, QldElectricity Supply Association of AustraliaGrain Handling authority of N.S.W.Insurance Council of AustraliaRoyal Australian Chemical InstituteState electricity regulatory authoritiesThe Pipeline Authority

Review of Australian Standards. To keep abreast of progress in industry, Australian Standards are subjectto periodic review and are kept up to date by the issue of amendments or new editions as necessary. It isimportant therefore that Standards users ensure that they are in possession of the latest ed ition, and anyamendments thereto.Full details of all Australian Standards and related publications will be found in the Standards AustraliaCatalogue of Publications; this information is supplemented each month by the magazine The AustralianStandard, which subscribing members receive, and which gives details of new publications, new editionsand amendments, and of withdrawn Standards.Suggestions for improvements to Australian Standards, addressed to the head office of Standards Australia,are welcomed. Notification of any inaccuracy or ambiguity found in an Australian Standard should be madewithout delay in order that the matter may be investigated and appropriate action taken.

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AS 2430.11987

Australian Standard

Classification of hazardous areasPart 1: Explosive gas atmospheres

First published . . . . . . . . . . . . . . . . . . . . . . . . 1981Second edition . . . . . . . . . . . . . . . . . . . . . . . . 1982Third edition . . . . . . . . . . . . . . . . . . . . . . . . . . 1987

PUBLISHED BY STANDARDS AUSTRALIA(STANDARDS ASSOCIATION OF AUSTRALIA)1 THE CRESCENT, HOMEBUSH, NSW 2140

ISBN 0 7262 4493 7

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AS 2430.11987 2

PREFACE

This edition of this standard was prepared by the Associations Committee onClassification of Hazardous Locations to supersede AS 2430, Part 11982. Thestandard is intended for the guidance of industry and relevant statutory authoritiesconcerned with the classification of hazardous areas. It is Part 1 of a series dealingwith specified hazardous atmospheres.This standard deals with the classification of hazardous areas according to theprobability of the existence of an explosive mixture of gas, vapour or mist with air inthe atmosphere.The content of this standard is solely concerned with the classification of hazardousareas and not with the types of equipment or ignition sources which can be used insuch areas. Such types of equipment are covered in standards published by the specifictechnology group, i.e. electrical, mechanical, gas, chemical.In its terminology, definitions and general treatment of the subject, this standard issimilar to the following report issued by the International ElectrotechnicalCommission:IEC 79 Electrical Apparatus for Explosive Gas Atmospheres

Part 10: Classification of Hazardous AreasThe major changes between this standard and the previous edition are as follows:(a) Closer alignment with IEC 79-10.(b) The addition of some important clarifications in the Scope and Application

Clauses.(c) The elimination of the two time criterion methods for determining hazardous

areas and distinguishing between Zones 0, 1 and 2.(d) The removal of the specific occupancy Appendix from this standard. (It is now

published as AS 2430, Part 3.)

CONTENTSPage

FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 REFERENCED DOCUMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 BASIC PRINCIPLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 DETERMINATION OF THE TYPE AND EXTENT OF ZONES . . . . . 78 VENTILATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 PROPERTIES OF FLAMMABLE LIQUIDS, GASES AND VOLATILE

SOLIDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

APPENDIX A. SOURCES OF RELEASE . . . . . . . . . . . . . . . . . . . . . . . . 10

Copyright STANDARDS AUSTRALIAUsers of Standards are reminded that copyright subsists in all Standards Australia publications and software. Except where theCopyright Act allows and except where provided for below no publications or software produced by Standards Australia may bereproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in writing fromStandards Australia. Permission may be conditional on an appropriate royalty payment. Requests for permission and information oncommercial software royalties should be directed to the head office of Standards Australia.

Standards Australia will permit up to 10 percent of the technical content pages of a Standard to be copied for useexclusively in-house by purchasers of the Standard without payment of a royalty or advice to Standards Australia.Standards Australia will also permit the inclusion of its copyright material in computer software programs for no royaltypayment provided such programs are used exclusively in-house by the creators of the programs.

Care should be taken to ensure that material used is from the current edition of the Standard and that it is updated whenever theStandard is amended or revised. The number and date of the Standard should therefore be clearly identified.The use of material in print form or in computer software programs to be used commercially, with or without payment, or incommercial contracts is subject to the payment of a royalty. This policy may be varied by Standards Australia at any time.

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3 AS 2430.11987

FOREWORD

Many gases, vapours and dusts which are generated processed, handled and stored inindustry are combustible. When ignited they may burn rapidly and with considerableexplosive force if mixed with air in the appropriate proportions.Areas where gases and vapours, dusts, flyings the fibres occur in dangerous quantitiesare classified as hazardous. This standard deals with the zonal classification ofhazardous areas where explosive gas atmospheres are present. For classification ofcombustible dust areas, refer to AS 2430, Part 2.The word zone is internationally accepted as indicating the probability of thepresence of a flammable, combustible or explodable material, and the extent,dimension, shape of hazardous area and volume in which the hazardous material canbe expected.This standard covers the following zones:ZONE 0: In which an explosive gas atmosphere is present continuously, or is

present for long periods.ZONE 1: In which an explosive gas atmosphere is likely to occur in normal

operation.ZONE 2: In which an explosive gas atmosphere is likely to occur in normal

operation and if it does occur it will exist for a short period only.The area classification should be carried out by those who have full knowledge bothof the processes, systems and equipment concerned and of safety and personnel. Theagreement reached on the area classification should be formally recorded.The properties (which are relevant to area classification) of all process materialsshould be listed and should include flashpoint, boiling point, melting point, ignitiontemperature, ignition energy, vapour pressure, vapour density and flammability limits.The initial step is to decide if a process item contains flammable material and if arelease can occur. The procedure outlined herein should be applied to each item ofequipment. The type and extent of the zonal areas can then be established.

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AS 2430.11987 4

STANDARDS ASSOCIATION OF AUSTRALIA

Australian Standardfor

CLASSIFICATION OF HAZARDOUS AREAS

PART 1 EXPLOSIVE GAS ATMOSPHERES

1 SCOPE. This standard provides guidance for theclassification of hazardous areas according to theexistence of or likelihood of the existence of an explosivegas/air mixture.

NOTE: Areas classified as Zones 0, 1 or 2 in accordance with thisstandard are sometimes referred to as Class I areas.

It applies to open and enclosed areas, in all above-groundsituations, where there may be a risk due to the presenceof flammable gas or vapour mixed with air under normalatmosphere conditions (see Note 1).This standard does not apply to (a) underground workings including coal mining;(b) processing and manufacture of explosives;(c) areas which may be affected by oxygen enrichment;(d) areas where risks may arise due to the presence of

combustible dusts (see Note 3); or(e) potential catastrophic failures such as the bursting of

pressure vessels, pipelines or tanks.NOTES:1. Normal atmospheric conditions include variations above and

below reference levels of 101.3 kPa and 20C provided thevariations have a negligible effect on the explosion properties ofthe flammable materials.

2. The design, construction and installation of plant and equipmenthave a significant bearing on classification. However, thisstandard does not specify any requirements for such design,construction or installation.

3. The classification of hazardous areas where combustible dusts arepresent (Class II areas) is covered in AS 2430, Part 2.

2 APPLICATION. This standard is intended forapplication by occupiers of premises and sites for thepurpose of recognizing and classifying hazardous areas.

NOTES:1. Responsibility for the recognition and classification of hazardous

areas is normally vested in the occupier.2. Where a statutory authority has jurisdiction, it may be necessary

to have the classification arrived at by the occupier ratified by thestatutory authority.

3. If necessary, the occupier should seek assistance from thosecompetent in classification principles and procedure. Statutoryauthorities normally do not perform this function.

3 REFERENCED DOCUMENTS. The followingdocuments are referred to in this standard:AS 1940 SAA Flammable and Combustible Liquids

CodeAS 2106 Methods for the Determination of the

Flashpoint of Flammable Liquids (ClosedCup)

AS 2430 Classification of Hazardous AreasPart 2 Combustible DustsPart 3 Specific Occupancies

NFPA 325M Fire Hazard Properties of FlammableLiquids, Gases and Volatile Solids

4 DEFINITIONS. For the purpose of this standard,the following definitions apply:4.1 Area, hazardous - an area in which an explosiveatmosphere is present, or may be expected to bepresent, in quantities such as to require specialprecautions for the construction, installation and use ofpotential ignition sources.

NOTES:1. For the purpose of this standard, an area is regarded as a

three-dimensional region or space.2. Examples of potential ignition sources are electrical equipment,

naked flames, sparks from grinding and welding operations, andhot surfaces.

4.2 Area, non-hazardous an area in which anexplosive atmosphere is not expected to be present inquantities such as to require special precautions for theconstruction, installation and use of potential ignitionsources.

4.3 Authority, Statutory the person or bodyresponsible for the implementation of legislationrelating to the handling, processing or storage ofmaterials constituting a hazard.4.4 Boiling point the temperature of a liquidboiling at an ambient pressure of 101.3 kPa.

NOTE: For liquid mixtures, the initial boiling point should beused. Initial boiling point in respect of liquid mixtures indicatesthe lowest value of the boiling point for the range of liquidspresent.

4.5 Explosive gas atmosphere mixture with air,under normal atmospheric conditions (see Clause 1,Note 1), of flammable materials in the form of gas,vapour, or mist, in which, after ignition, combustionspreads throughout the unconsumed mixture.

NOTES:1. This definition specifically excludes dusts and fibres in

suspension in air.2. Although a mixture which has a concentration above the upper

explosive level (UEL) is not an explosive gas atmosphere, incertain cases for area classification purposes it is advisable toconsider it as an explosive gas atmosphere.

4.6 Explosive limit, lower (LEL) the concentra-tion of flammable gas, vapour or mist in air, belowwhich an explosive gas atmosphere will not be formed.4.7 Explosive limit, upper (UEL) the concen-tration of flammable gas, vapour or mist in air, abovewhich an explosive gas atmosphere will not be formed.4.8 Flammable gas or vapour - gas or vapour which,when mixed with air in certain proportions, will forman explosive gas atmosphere.

NOTE: All vapours of flammable liquids are flammable vapours.

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4.9 Flammable liquid any Class 3.1 (Class A) orClass 3.2 (Class B) liquid having a flashpoint of not morethan 61C.

NOTES:1. AS 1940 defines a Class A flammable liquid as a flammable

liquid having a flashpoint up to but not including 23C, and aClass B flammable liquid as a flammable liquid having aflashpoint not less than 23C and up to and including 61C.

2. In accordance with the above definition, kerosine and white spiritare flammable liquids whereas diesel fuel (distillate) is not.

4.10 Flammable material material consisting offlammable gas, vapour, liquid and/or mist.4.11 Flammable mist droplets of flammable or com-bustible liquid, dispersed in air, so as to form anexplosive atmosphere.4.12 Flashpoint the lowest liquid temperature atwhich, under certain standardized conditions, a liquidgives off vapours in quantity such as to be capable offorming an ignitable vapour/air mixture.

NOTES:1. Flashpoint data are normally associated with liquids, though they

are also relevant to solids which sublime. It is important to notethat care must be taken in the use of flashpoint data inapplications where the ignition source may itself raise thetemperature of the combustible material.

2. The value for the flashpoint depends to some extent on themethod of test. For the purpose of this standard, flashpoints aredetermined in accordance with the relevant requirements ofAS 2106.

4.13 Normal operation the situation when the plantequipment is operating within its design parameters.

NOTES:1. Minor releases of flammable material may be part of normal

operation. For example, releases from seals which rely on wettingby the fluid being pumped are considered to be minor releases.

2. Failures (such as the breakdown of pump seals, flange gaskets orspillages caused by accidents) which involve repair or shut downare not considered to be part of normal operation.

4.14 Relative density (of a gas or vapour) thedensity of a gas or a vapour relative to the density of airat the same pressure and at the same temperature.

NOTE: The relative density of air is 1.0.

4.15 Source of release a point or location fromwhich a gas, vapour, mist or liquid may be released intothe atmosphere so that an explosive gas atmosphere couldbe formed.

4.16 Ventilation, general artificial movement of airand its replacement with fresh air by artificial means (e.g.fans) and applied to a general area.4.17 Ventilation, local artificial movement of air andits replacement with fresh air by artificial means (usuallyextraction) applied to a particular source of release orlocal area.

4.18 Ventilation, natural movement of air and itsreplacement with fresh air due to the effects of windand/or buoyancy forces.

4.19 Ventilation, no exists where no arrangementshave been made to cause air replacement with fresh air.

4.20 Zones, hazardous - the zones into which hazardousareas are classified based upon the frequency of theappearance and the duration of an explosive gasatmosphere.

4.21 Zone 0 - an area in which an explosive gasatmosphere is present continuously or is present forlong periods.

4.22 Zone 1 - an area in which an explosive gasatmosphere is likely to occur in normal operation.

4.23 Zone 2 - an area in which an explosive gasatmosphere is not likely to occur in normal operationand if it does occur it will exist for a short period only.

NOTE: This zone applies to areas where flammable materials areused but where an explosive gas atmosphere would occur only inthe event of an accident or some unusual operating condition. Thiszoning may also apply to the interface between a Zone 1 area anda non-hazardous area.

5 GENERAL. Area classification is a method ofanalyzing and classifying the environment whereexplosive gas atmospheres may occur to allow theproper selection of equipment, particularly electricalequipment, to be installed in that environment.The object of the classification procedure is to enablethe equipment to be operated safely in theseenvironments.Where it is necessary to use equipment in anenvironment in which there may be an explosive gasatmosphere and it is not possible to:(a) eliminate the likelihood of an explosive gas

atmosphere occurring around the source ofignition, or

(b) eliminate the source of ignition;then measures should aim at reducing the likelihood ofthe occurrence of either or both of the above factors sothat the likelihood of coincidence is so small as to beacceptable.In most practical situations where flammable materialsare used it is difficult to ensure that an explosive gasatmosphere will never occur. It may also be difficult toensure that equipment will never give rise to a sourceof ignition. Therefore in situations where an explosiveatmosphere has a high likelihood of occurring, relianceis placed on using equipment which has an extremelylow likelihood of creating a source of ignition.Conversely where the likelihood of an explosiveatmosphere occurring is reduced, equipment which hasan increased likelihood of becoming a source of ignitionmay be used. To apply this approach the first step is toassess the likelihood of an explosive atmosphereoccurring in accordance with the definitions of Zone 0,Zone 1 and Zone 2. The following clauses giveguidance on this first step, viz: on the classification ofareas in which there may be an explosive gasatmosphere into Zones 0, 1 and 2.

6 BASIC PRINCIPLES.6.1 Fundamental safety concepts. It is recommendedthat plants and installations in which flammablematerials are handled or stored be so designed thathazardous areas are kept to a minimum; in particularZone 0 and Zone 1 areas should be a minimum in bothnumber and extent. In other words the hazardous areasshould be mainly Zone 2. Where release of flammablematerial is unavoidable, plant equipment items shouldbe mainly limited to secondary grade sources of release,or failing this (that is where primary or continuousgrade sources of release are unavoidable) the sources ofrelease should be such as to have a very limitedquantity or rate of release to atmosphere. In carrying

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out area classification, these principles should receiveprime consideration and where necessary, the design,operation or location of process equipment should bemodified to meet these requirements. Similarly,consideration should be given to the design and operationof process equipment to ensure that even when it isoperating abnormally the amount of flammable materialreleased to the atmosphere is minimized in order toreduce the extent of the area (Zone 2) made hazardous.Where the situation is covered in AS 2430, Part 3, theclassification given therein should be used, provided acareful check is made to ensure that the specificoccupancy specified is appropriate to the case underconsideration. Where the occupancy is not specified inAS 2430, Part 3, or where unusual circumstances apply,the procedure illustrated in Fig. 1 may be used.Once a plant has been classified and any necessaryrecords made it is important that no modification toequipment or operating procedures is made withoutdiscussion with those responsible for the areaclassification. Unauthorized action may invalidate the areaclassification.It is necessary to ensure that process equipment whichhas been subjected to maintenance shall be carefullychecked during and after re-assembly to ensure that theintegrity of the original design as it affects safety, hasbeen maintained before it is returned to service.It should be recognized that the opening of parts ofclosed process systems (e.g. filter changing, batch filling)should also be considered as sources of release indeveloping the area classification.6.2 Factors which determine type and extent of zones.6.2.1 Type of zone. The likelihood of the presence of anexplosive gas atmosphere and hence the type of zonedepends mainly on the grade of source of release. Insome cases the ventilation and other factors may alsoaffect the type of zone.To facilitate the classification of areas, this standard givessome typical and specific examples (see Figs 5 and 6)which may be used where they are applicable to thesituations under consideration. Where the examples do notstrictly apply a classification may be arrived at byadjusting those examples to the actual conditions andusing the logic typified in Fig. 1. Where the actualconditions are not related to the examples, additionalconsiderations should be introduced in the classificationprocedure. For open air unrestricted ventilated situations,Fig. 1 may be used.Depending on conditions of release and subsequentpropagation, it may be necessary in some cases to requirea less hazardous zone surrounding a more hazardouszone.

6.2.2 Extent of zone. The extent of zones depends mainlyon the following parameters:(a) Release rate of flammable material. The extent may

increase with increasing release rate (but see releasevelocity).

(b) Release velocity. Due to an improved dilution forrelease of flammable gases, vapours and/or mists inair, the extent of a hazardous area may decrease if,with constant release rate, the release velocityincreases above that which causes turbulent flow.

(c) Concentration of flammable gases, vapours and/ormists in the released mixture. The extent mayincrease with increasing concentration at the releasesource.

(d) Ventilation. With an increased rate of ventilation, the

extent of a hazardous area may be reduced. The extentmay also be reduced by an improved arrangement ofthe ventilation system.(e) Obstacles. Obstacles may impede the ventilation

and thus may enlarge the extent of the zone. Onthe other hand some obstacles, for example dikesand walls, may limit the movement of a cloud ofan explosive gas atmosphere and thus may reducethe extent.

(f) Boiling point of flammable liquids (initial boilingpoint for liquid mixtures). For flammable liquids,the concentration of the released vapour is relatedto the vapour pressure at the relevant maximumliquid temperature. The lower the initial boilingpoint, the greater the vapour pressure for a givenliquid temperature and hence the greater the extentof the hazardous area.

(g) Lower explosive limit. The lower the LEL, thelarger may be the extent of the hazardous area.

(h) Flashpoint. An explosive gas atmosphere cannotexist if the flashpoint is significantly above therelevant maximum temperature of the flammableliquid. The lower the flashpoint, the larger may bethe extent of the hazardous area. Some liquids(such as certain halogenated hydrocarbons) do notpossess a flashpoint although they are capable ofproducing an explosive gas atmosphere; in thesecases the equilibrium liquid temperaturecorresponding to saturated concentration at LELshould be compared with the relevant maximumliquid temperature.NOTE In special conditions the mist of a flammable orcombustible liquid may be released at a temperature below theflashpoint and may therefore produce an explosive gasatmosphere.

(j) Relative density. The horizontal extent of ahazardous area may increase with increasingrelative density. Where the relative density is lessthan unity, the vertical extent may increase with adecrease in relative density.

(k) Liquid temperature. The extent of a hazardous areamay increase with increasing temperature ofprocess liquid provided the temperature is abovethe flashpoint. It should be noted that the liquid orvapour temperature after the release may beincreased or decreased by the ambient temperatureor other factors (e.g. a hot surface).

6.3 Grading of source of release (see alsoAppendix A). Each item of process equipment (e.g.tank, pump, pipeline, vessel etc.) should be consideredas a potential source of release of flammable material.If the item cannot contain flammable material it willclearly not give rise to a hazardous area around it. Thesame will apply if the item contains a flammablematerial but cannot release it to atmosphere (e.g. anall-welded pipeline is not a source of release).If it is established that the item may release flammablematerial to the atmosphere, (as will be the case withmost items) it is necessary, first of all, to determine thegrade of the source of release.By means of this procedure each item will be gradedeither Continuous, Primary, Secondary, orMulti-grade .The source grade should be estimated by consideringoperational openings to atmosphere and the possibilityof releases under all (normal and abnormal) operatingconditions of the plant, installation or process.

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7 DETERMINATION OF THE TYPE ANDEXTENT OF ZONES.7.1 General. Having established the grade of the releasesource it is necessary to determine the release rate fromthe item and, furthermore, the other necessary factorswhich may influence the type and extent of the hazardousarea, as mentioned in Clause 6.2 (and illustrated in Figs 5and 6).It is rarely possible by cursory examination of a plant orplant design to decide which parts of the plant can beequated to the three zonal definitions (Zones 0, 1 and 2).A more objective approach is therefore necessary andinvolves the analysis of the basic possibility of anexplosive gas atmosphere occurring. Since an explosivegas atmosphere can exist only if a flammable gas, vapouror mist is present with air, it is necessary to decide if anyof these flammable materials can exist in the areaconcerned. Generally speaking such materials (and alsoflammable liquids and solids which may give rise tothem) are contained within process equipment which mayor may not provide a totally enclosed containment. Todiscover the cause of an explosive gas atmosphereexisting in an area it is necessary therefore to determinehow the items of process equipment containing flammablematerials can release them to atmosphere. Once the likelyfrequency and duration of release (and hence the grade ofsource of release), the release rate, concentration,velocity, ventilation and other factors which affect thetype of zone and/or extent of the hazardous area havebeen determined, there is then a firm basis on which todetermine the likely presence of an explosive gasatmosphere in the surrounding areas. This approachtherefore requires detailed consideration to be given toeach item of process equipment which contains aflammable material, and which could therefore be asource of release. In some cases there may be otherconsiderations (e.g. consequential damage) which maycall for a different classification but these considerationsare outside the scope of this Standard.It is often convenient to carry out an area classificationstudy in tabular form. An example of such a table isshown in Fig. 2, which should also include details ofapparatus group and temperature classification. When theextent of each zone surrounding each source of releasehas been determined, the composite area classificationdrawing can be produced. An example of such a drawingis shown in Fig. 3. The preferred way of indicating thezones is shown in Fig. 4.

NOTE: Consideration should be given to the possibility that anexplosive gas atmosphere may flow into areas in the soil belowground level such as cavities, pits and depressions.

7.2 Open air unrestricted ventilated situations.7.2.1 Procedure. A procedure which may be adopted indetermining the type and extent of zones around aparticular process equipment item is illustrated in Fig. 1.

NOTE: The following text is given in explanation of the steps in thefigure and should be read in conjunction with it. The numbers whichappear in the text are the box numbers in the figure.

7.2.2 Quantity of flammable material. It is first necessaryto determine whether the process equipment item containsmore than a specified minimum quantity of flammablematerial specified by relevant regulation or standard (e.g.AS 1940). If there is no relevant regulation or standard,refer to Fig. 1. (1 and 2). If it does not, the area aroundit will be non-hazardous (32). Should it contain more thanthe specified minimum it is necessary to determine (3) ifrelease of the flammable material is possible (neglecting

catastrophic events such as the bursting of processvessels, large pipelines or tanks). If it is not possible,the area around the process equipment item will benon-hazardous (32). Should release be possible thegrade of source of release should be determined inaccordance with the definitions in Appendix A. Itshould be noted that the grade of source of release isdependent only on the frequency and duration ofrelease.

7.2.3 Sources of release graded continuous. Wherethe process equipment item is graded as continuous(5) consideration should be given to improving theprocess equipment item to reduce the frequency and/orduration of release of the flammable material (6).Where significant improvement is possible the processequipment item may be regraded as a primary (18) ora secondary (27) grade source of release. Where suchimprovement is not possible the release rate, concentra-tion, velocity, ventilation and the other factors whichaffect the type and extent of zone should be determined(7) and, where possible, modified so as to reduce theextent.When these factors have been modified as much aspossible, the distance from the process equipment itemto the point at which the vapour/air mixture is belowthe lower explosive limit* should be determined takinginto account the release rate, concentration, velocity,ventilation and the other necessary factors, basing thedistance on a chosen low wind speed (8) for the districtconcerned. The distance so determined is the extent ofthe Zone 0 from the source (9) (see Note at the end ofClause 7.2.5).It is then necessary to determine whether release fromthe same process equipment item as a primary gradesource of release is likely (10). This is of consequenceonly if the release rate, concentration or manner ofrelease is such as to result in a distance to the LELgreater than that in the continuous mode for the samechosen low wind speed. If this is the case the distancefrom the process equipment item to the lower explosivelimit (12) should be determined. This distance is theextent of the Zone 1 from the source (13) (see Note atthe end of Clause 7.2.5). Where the distance is notgreater than in the continuous mode there will be noresultant Zone 1(11).Consideration should then be given to the likelihood ofrelease from the same process equipment item as asecondary grade (14) source of release. This is ofconsequence only where the release rate, concentrationor manner of release is such as to result in a distance tothe LEL greater than that in the primary grade mode(12) for the same chosen low wind speed. If this is thecase the distance to the lower explosive limit (16)should be determined. This distance is the extent of theZone 2 from the source (17). Where the distance is notgreater than in the primary grade mode there will be noresultant Zone 2 (15).An example of a process equipment item graded ascontinuous is an open vessel of volatile liquid whichreleases a small rate of vapour continuously (continuousgrade) giving rise to a small Zone 0 (9) but where theliquid is subject to frequent rises in temperature which

* Consideration should be given to a need for a safety factor on LEL(e.g. a value lower than LEL).

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cause it to release as a primary grade source at a greaterrate giving rise to a larger Zone 1(13) and whereinfrequent spillage of the liquid causes it to act as asecondary grade source giving rise to a larger Zone 2(17). The process equipment item is therefore behaving asa multigrade source of release giving rise to the threezonal classifications based on different release rates andthe same chosen low wind speed (see Note at the end ofClause 7.2.5).7.2.4 Sources of release graded primary. Should theitem be graded as primary (18), a procedure similar tothat described above and illustrated in boxes (19) to (26)should be followed.An example of a process equipment item graded asprimary is the seal of a pump handling a volatile liquidwhere the conditions are such that it releases a small rateof liquid or vapour frequently (primary grade) giving riseto a small Zone 1(22) but where failure of the pump sealoccurs infrequently (secondary grade) releasing liquid orvapour at a higher rate thus giving rise to a larger Zone2 (26). The process equipment item is therefore behavingas a multigrade source of release giving rise to two zonalclassifications based on different release rates and thesame chosen low wind speed (see Note at the end ofClause 7.2.5).7.2.5 Sources of release graded secondary. Should theprocess equipment item be graded secondary (27), aprocedure similar to that described above and illustratedin boxes (28) to (31) should be followed.An example of a process equipment item graded assecondary is the seal of a pump or pipe flange wherethere is no frequent release but where failure of the sealor gasket will occur infrequently (secondary grade) givingrise to a Zone 2 (31) around the process equipment itembased on the release rate and the same chosen low windspeed.

NOTE: This explanation is based on the single low wind speedconcept. Where it is considered that lower wind speeds prevail forsufficiently high percentages of the total time in a year, distancesbased on this lower wind speed may also be calculated. The distancesso determined will give rise to zones of higher number but of greaterextent than those using the original wind speed.

7.3 Situations other than those in the open air. Asimilar procedure to that described in Clause 7.2 may beused for determining the type and extent of zones in otherthan open air situations. It is not considered practical toinclude standard figures to cover these situations but it issuggested that for particular situations Fig. 1 can be usedas a basis provided modifications are introduced to coverspecial features such as differing degrees of natural orartificial ventilation, and the presence of obstructions.Reference should be made to Clause 6.2 and Clause 8.

8 VENTILATION.8.1 General. Gas or vapour released to the atmospherecan be diluted by dispersion or diffusion in the air untilits concentration is below the lower explosive limit.Ventilation, that is air movement, will promote dispersion.The degree of ventilation, for example number of airchanges per hour, may affect the type and/or extent ofzones. The most important factor is that the design ofventilation is related to the source of release in order toachieve optimal ventilation conditions in the hazardousarea. In considering the effect of ventilation, the relativedensity of the gases or vapours is important and shouldreceive special consideration in determining theventilation arrangements.

The following main types of ventilation are recognized:(a) Natural ventilation.(b) General artificial ventilation.(c) Local artificial ventilation.

NOTE: It should be noted that the above terms are related tothe type and not to the degree of ventilation.

It is also necessary to recognize:(d) No ventilation.8.2 Natural ventilation. Examples are:(a) Open air situations typical of those in the chemical

and petroleum industries which comprise openstructures, pipe racks, pump bays and the like.

(b) An open building which, having regard to therelative density of the gases and/or vapoursinvolved, has openings in the walls and/or roof sodimensioned and located that the ventilation insidethe building for the purpose of area classification,can be regarded as equivalent to that in an open airsituation.

(c) A building which is not an open building butwhich has natural ventilation (generally less thanthat of an open building) provided by permanentopenings made for ventilation purposes.

8.3 General artificial ventilation. Examples are:(a) A building which is provided with fans in the

walls and/or in the roof to improve the generalventilation in the building.

(b) An open air situation provided with suitablylocated fans to improve the general ventilation ofthe area.

8.4 Local artificial ventilation. Examples are:(a) An air/vapour extraction system applied to a

process machine or vessel which continuously orperiodically releases flammable vapour.

(b) A forced or extract ventilation system applied to asmall inadequately ventilated local area where it isexpected that an explosive atmosphere mayotherwise occur.

8.5 No ventilation. An example of an area with noventilation is an enclosure or room having nopermanent opening.

NOTE: In a large building, the volume of which is large comparedwith the hazardous area around the source of release, that areaneed not necessarily be considered to have no ventilation.

8.6 Relationships between grades of source ofrelease, ventilation and type and extent of zone.8.6.1 Natural and general artificial ventilation. Acontinuous grade source of release may lead to a Zone0, a primary grade to a Zone 1 and a secondary gradeto a Zone 2. In some cases, however, the degree ofventilation may be so good that the extent of the zonemay be so small as to be negligible or the zone mayhave a higher number or in the end may becomenon-hazardous. On the other hand, the degree ofventilation may be so poor that the zonal classificationwill have a larger extent and in some cases a lowerzone number (see Clause 8.6.5).

NOTE: For open air situations, the zone number and extent can bedetermined from Fig. 1.

8.6.2 Local artificial ventilation. Local artificialventilation will usually be more effective than naturaland general artificial ventilation in diluting explosive

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gas-air mixtures. As a consequence, the extent of thezones will be reduced and in some cases will be so smallas to be negligible or the zone will have a higher numberor may become non-hazardous (see Clause 8.6.5).8.6.3 No ventilation. Where a source of release is withinan area with no ventilation, a continuous grade will, anda primary grade may, lead to a Zone 0 and a secondarygrade may lead to a Zone 1. Where there are specialfactors, for example very infrequent release and/ormonitoring of the release, higher zone numbers mayapply.

8.6.4 Ventilation restricted by obstacles. Some obstacleswhich exist in the area may impede the ventilation localto the obstacles and may thus require a larger extentand/or a lesser zone number in the local area. Inconsidering the effect of obstacles, especially in the caseof pits and pockets some of which may be inverted,particular attention should be paid to the relative densityof the gases and vapours involved (see item(e) ofClause 6.2.2).8.6.5 Consequences of artificial ventilation failure. Thearea classification should be established assuming that theventilation is in operation since this will be the normalcondition. The risk of ventilation failure should then beestablished. If the risk of failure is negligible (e.g.because an automatic independent stand-by system isprovided) the area classification determined with theventilation operating will not need modification. Howevershould there be a risk of failure of the ventilation, the

likely frequency and duration should be establishedtogether with the extent of spread of explosive gasatmosphere in the absence of artificial ventilation. Thisextent of spread may be greater (see Note) than that ofthe area classification extent already determined withthe ventilation operating. The zone number(s) of thewhole area under consideration with ventilation off willdepend on the likely frequency and duration ofventilation failure and on the classification determinedwith the ventilation on.Where the ventilation is likely to fail infrequently andfor short periods, the additional area (see Note) due toventilation failure need have a zone number no lessthan 2.If provision is made to prevent release of flammablematerial when the ventilation has failed (e.g. byautomatically closing down the process) theclassification determined with the ventilation operatingneed not be modified.

NOTE: The electrical installation in the additional area need not besuitable for the zone of this area if provision is made to switch offsuch electrical installation on ventilation failure.

9 PROPERTIES OF FLAMMABLE LIQUIDS,GASES AND VOLATILE SOLIDS. This standarddoes not contain information on the properties offlammable liquids, gases and volatile solids. However,information may be obtained from NFPA 325M.

NOTE: Copies of NFPA 325M are available for examination atSAA libraries in Sydney and Melbourne. Copies of NFPA 325Mare also available for purchase from the SAA sales office inSydney.

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APPENDIX ASOURCES OF RELEASE

A1 SCOPE. This Appendix describes the grades of sources of release and givesexamples.A2 GRADES OF SOURCES OF RELEASE.A2.1 General. There are three basic grades of source of release as listed below inorder of decreasing likelihood to the release occurring:(a) Continuous grade.(b) Primary grade.(c) Secondary grade.A2.2 Continuous grade source of release. A source which will release continuouslyor is expected to release for long periods or for short periods which occur frequently.

A2.3 Primary grade source of release. A source which can be expected to releaseperiodically or occasionally during normal operation.

A2.4 Secondary grade source of release. A source which is not expected to releasein normal operation and if it releases is likely to do so only infrequently and for shortperiods.

NOTE: A source of release which is a combination of two or three of the above grades, is gradedcontinuous or primary.

A source of release which is basically graded continuous may in addition be gradedprimary if the rate of release of flammable material, for the primary grade frequencyand/or duration, exceeds that for the continuous grade.It may, additionally or alternatively to the primary grade, also be graded secondary ifthe rate of release of flammable material, for the secondary grade frequency and/orduration, exceeds that for the continuous and, if applicable, the primary grade.Similarly a source of release which is basically graded primary may in addition begraded secondary if the rate of release of flammable material for the secondary gradefrequency and/or duration exceeds that for the primary grade.A3 EXAMPLES OF SOURCES OF RELEASE.A3.1 General. The following are examples of the grading of some sources of release.The examples are not intended to be rigidly applied and may need to be varied to suitparticular equipment, situations and national practices.

A3.2 Continuous grades of release.(a) The surface of a flammable liquid in a non-inerted fixed-roof tank.(b) The surface of a flammable liquid which is open to the atmosphere. (May apply

to oil-water separators.)(c) Free vents and other openings which release flammable gas or vapour to

atmosphere frequently or for long periods.

A3.3 Primary grades of release.(a) Seals of pumps, compressors and valves if release during normal operation of the

equipment is expected.(b) Process equipment water drains located on tanks containing flammable liquids

which may release flammable material to atmosphere when draining off waterduring normal operation.

(c) Sample points which are expected to release flammable material to atmosphereduring normal operation.

A3.4 Secondary grades of release.(a) Seals of pumps, compressors and valves where release during normal operation

of the equipment is not expected to occur.(b) Flanges, connections and pipe fittings.(c) Relief valves, vents and other openings which are not expected to release

flammable gas or vapour to atmosphere during normal operation.(d) Sample points which are not expected to release flammable material to atmosphere

during normal operation.

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Fig. 1. THEORETICAL APPROACH TO THE DETERMINATION OF TYPE AND EXTENT OF ZONESFOR OPEN AIR UNRESTRICTED VENTILATION SITUATIONS

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Process equipment itemFlammable

material

Processtemperature

andpressure

Description offlammablematerial

containmentVentilation

Source of release Horizontal distance from source to* Codereference RemarksNo. Description Location Description Grade Boundaryof Zone 0

Boundaryof Zone 1

Boundaryof Zone 2

Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Column 7 Column 8 Column 9 Column 10 Column 11 Column 12 Column 13 Column 14C 52 Hydrogen

vesselArea 2 inopen air

Hydrogen 30C2 500 kPa

Closed systemwith valves, reliefvalve to flare

Natural(open air)

Flangesand valveseals (seecol. 14)

Secondary m XYZNationalCode,page XY

Release due toflange gasket orvalve sealfailures(abnormal)

J 29 Xylenepump

Area 5 inopen air

Xylene 80C300 kPa

Closed systemwith valves anddrains.Mechanical sealsand throttle bush

Natural(open air)

Flangesand valveseals (seecol. 14)

Secondary m XYZNationalCode,page XX

Release due toflange gasket orvalve sealfailures(abnormal)

Mechanicalseal (seecol. 14)

Primary/secondary(multigrade)

m m XYZNationalCode,page YX

Small release innormaloperation. Largerrelease on sealfailure(abnormal)

J 94 Ethylenecompressor(reciprocating)

Area 4 inopenbuilding

Ethylene 70C2 000 kPa

Closed systemwith glands,vents and coolerdrain points

Natural(equivalentto openair)

Flanges,glandsand valveseals (seecol. 14)

Secondary m XYZNationalCode,page XZ

Releases due toflange gasket,gland or valveseal failures(abnormal)

Vents anddrainpoints (seecol. 14)

Primary/secondary(multigrade)

m m XYZNationalCode,page ZX

Small releases innormaloperation. Largerrelease mayoccur due toincorrectoperation(abnormal)

J 32 Fixed rooftank

Area 3 inopen air

Gasoline Ambient Closed systemexcept forpressure/vacuumvalve

Natural(open air)

Tank vent(see col. 14)

Continuous/primary/secondary(multigrade)

Zone 0 invapourspace

m m XYZNationalCode,page XZ

Vapour ventedduring normalfilling.Possibility ofoverfilling(abnormal)

* Vertical distances may also be recorded.

NOTE: Other information such as temperature class and apparatus group may need to be included.

Fig. 2 EXAMPLE OF TABLE FOR USE DURING AREA CLASSIFICATION STUDY

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NOTES:1. All dimensions are measured from sources of release.2. In some cases it may be more practical to establish the actual

boundary of a classified area at more convenient geographical limits.3. Details to be added where necessary regarding:

(a) Localized Zones 0 or 1.(b) Vertical distances of Zones 0, 1 and 2. In some cases it will be

necessary to draw sections to clarify vertical distances.(c) The title of the code which has been used as a basis for extent

of areas.(d) Apparatus group and temperature class for selection of electrical

apparatus.

Symbol DescriptionABCEFGH

J

K

LNM

Control room, pressurizedSwitch house, pressurizedWorkshopVesselDistillation columnDrainPump (seals unlikely to release innormal operation)Pump (seals likely to release innormal operation)Pump (seals likely to release innormal operation)Reciprocating compressorCompressor house (open building)Vents (high or low level)

NOTE: The above table is given for explanation of this drawing only. Itwill not appear on the completed area classification drawing.

Fig. 3. EXAMPLE OF AN AREA CLASSIFICATION DRAWING

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Fig. 4. PREFERRED SYMBOLS FOR THE ZONES OF A HAZARDOUS AREA

NOTES:

1. The diagrams relate to

(a) open air situations; and(b) sources of release near to ground level.

2. The shapes and sizes of the zones will depend on many factors(see Clause 6.2.2)

3. Zone 1 Zone 2

Fig. 5. EXAMPLE ILLUSTRATING AREA CLASSIFICATION AROUND VARIOUS SOURCES OFRELEASE FOR HEAVIER-THAN-AIR GASES OR VAPOURS

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NOTES:

1. The diagrams relate to

(a) open air situations;(b) sources of release above ground level; and.(c) gases which are significantly lighter than air.

2. The shapes and sizes of the zones will depend on many factors (see Clause 6.2.2)

3. Zone 1 Zone 2

Fig. 6. EXAMPLE ILLUSTRATING AREA CLASSIFICATION AROUND VARIOUS SOURCESOF RELEASE FOR LIGHTER-THAN-AIR GASES

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AS 2430.1-1987 Classification of hazardous areas - Explosive gas atmospheresAS 2430.1-1987 CLASSIFICATION OF HAZARDOUS AREAS - EXPLOSIVE GAS ATMOSPHERESPREFACECONTENTSFOREWORD1 SCOPE.2 APPLICATION3 REFERENCED DOCUMENTS4 DEFINITIONS4.1 Area, hazardous4.2 Area, non-hazardous4.3 Authority, Statutory4.4 Boiling point4.5 Explosive gas atmosphere4.6 Explosive limit, lower (LEL)4.7 Explosive limit, upper (UEL)4.8 Flammable gas or vapour4.9 Flammable liquid4.10 Flammable material4.11 Flammable mist4.12 Flashpoint4.13 Normal operation4.14 Relative density (of a gas or vapour)4.15 Source of release4.16 Ventilation, general artificial4.17 Ventilation, local artificial4.18 Ventilation, natural4.19 Ventilation, no4.20 Zones, hazardous4.21 Zone 04.22 Zone 14.23 Zone 2

5 GENERAL6 BASIC PRINCIPLES6.1 Fundamental safety concepts6.2 Factors which determine type and extent of zones6.2.1 Type of zone6.2.2 Extent of zone

6.3 Grading of source of release (see also Appendix A)

7 DETERMINATION OF THE TYPE AND EXTENT OF ZONES7.1 General7.2 Open air unrestricted ventilated situations7.2.1 Procedure7.2.2 Quantity of flammable material7.2.3 Sources of release graded `continuous'

8 VENTILATION8.1 General8.2 Natural ventilation8.3 General artificial ventilation8.4 Local artificial ventilation8.5 No ventilation8.6 Relationships between grades of source of release, ventilation and type and extent of zone8.6.1 Natural and general artificial ventilation8.6.2 Local artificial ventilation8.6.3 No ventilation8.6.4 Ventilation restricted by obstacles8.6.5 Consequences of artificial ventilation failure

9 PROPERTIES OF FLAMMABLE LIQUIDS, GASES AND VOLATILE SOLIDS.APPENDIX A - SOURCES OF RELEASEA1 SCOPE.A2 GRADES OF SOURCES OF RELEASEA2.1 GeneralA2.2 Continuous grade source of releaseA2.3 Primary grade source of releaseA2.4 Secondary grade source of release

A3 EXAMPLES OF SOURCES OF RELEASEA3.1 GeneralA3.2 Continuous grades of releaseA3.3 Primary grades of releaseA3.4 Secondary grades of release

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