pp2160 module 1 detection principles & device selection issue 3

7/31/2019 PP2160 Module 1 Detection Principles & Device Selection Issue 3

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PP2160/2009/Issue 3

Module 1

Detection Principles &Device Selection

36 Brookside Road, Havant, Hampshire, PO9 1JRTel: +44 (0)23 9249 2412 Fax: +44 (0)23 9249 2754

Website: www.apollo-fire.co.ukEmail: [email protected]


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Apollo Fire Detectors Limited 2004-2009

Contents

Detection principles & device selection 3

Life Protection 3

Property Protection 3

Detection Principles & Device Selection 4

Ionisation Smoke Detectors 5

Optical Smoke Detectors 7

Series 65 Optical Smoke Detectors 7

XP95 Optical Smoke Detectors 7

Heat Detectors 8

Multisensor Detectors 9

Selecting the Correct Device 11

Series 65 A1R Heat Detector, part nos 55000-120/121/122 12

Series 60 Grade 1 Heat Detector, part no 55000-100 12


Series 65 BR Heat Detector, part no 55000-125/126/127 12


Series 60 Range 1 Heat Detector, part no 55000-103 12

Series 65 CR Heat Detector, part no 55000-130/131/132 12

Series 60 Range 2 Heat Detector, part no 55000-104 12

Series 65 CS Heat Detector, part no 55000-135/136/137 12


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MODULE 1

Detection principles & device selectionOne of the most important factors to be considered when designing a fire alarm system iscompliance with standards and legislation applicable at the location of installation. In the UnitedKingdom, BS 58391 : 2002 is the primary standard. However, there may be rules or conditionswhich apply to a district or even a single building. The advice of the local Fire Prevention Officer

could be useful at the preliminary design stage of a project. With the inception of the RRFSOthe responsible person needs to carry out fire risk assessments and be more involved with thetechnical elements of the fire system.

British Standard BS 58391 : 2002 defines fire alarm systems as protection of life or protection ofproperty. System categories are:

Life ProtectionL1 All areas covered by detectors, giving the maximum degree of improvement to safety.

L2 All vulnerable areas covered by detectors. In this context, vulnerable refers to areas wherepeople are at risk and areas where potentially dangerous fires are likely to start. All escape

routes should be covered by the system.L3 Detectors covering escape routes and all adjoining areas except corridors less than 6m long.

L4 Escape routes including stairways.

L5 Selected areas (non-prescriptive, designers responsibility).

M The area is covered by manual call points but there are no automatic detectors.

Property ProtectionP1 All areas should be covered by automatic detection, allowing a fire to be discovered andextinguished before substantial damage occurs. P1 systems are necessary in buildings that

have areas that are unoccupied for long periods.

P2 Used in buildings where areas have a very low risk and automatic detection is not thoughtnecessary. Unprotected areas in this low risk category should be separated from protectedareas by fire-resistant construction.

When a category is selected, the next considerations are the degree of sophistication required andlimitations or freedoms imposed by factors such as building layout, construction and areas or zonesto be covered. The choice is either a zone-wired conventional system or an analogue addressablesystem.

In conventional systems, detectors are wired into a circuit (a zone). Detectors signal fire conditionsto a control panel by changing from high to low impedance. The panel detects this impedancechange by current monitoring and identifies the zone. Individual detectors cannot be identified. Azone could cover up to 2000m.


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Ionisation Smoke DetectorsIonisation smoke detectors manufactured by Apollo contain an inner reference chamber within anouter smoke chamber. A small radioactive source irradiates the air within the chambers resulting inthe air particles becoming ionised. Both positively and negatively charged ions are produced. Theradioactive source holder is the positive electrode and the outer smoke chamber is the negativeelectrode. The result is a small electric current that flows between the two. The current is derivedfrom the fact that the positively charged ions are drawn towards the negative electrode and

negatively charged ions are drawn towards the positive electrode.

When smoke particles enter the chamber, ions become attached to them with the result thatthe current flowing through the ionisation chamber decreases. This effect is greater in the smokechamber than in the reference chamber and the imbalance causes the sensing electrode tobecome more positive.

This type of detector gives a good response to fast burning, high energy/flaming type fires thatemit invisible smoke particles (


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Ionisation type detectors were the first type of commercial fire detector and were developedduring the 1950s. They are also used extensively in domestic environments.

The demand for ionisation detectors has decreased recently due to environmental concerns. Theseconcerns have resulted in higher costs of disposal and shipping and have also seen some citiesand even countries become radioactive free zones. In this country the use of radioactive sources iscontrolled and monitored by the National Radiological Protection Board (NRPB).

Ionisation detectors are fitted with anti-tamper screws to make them difficult to open and, in fact,the regulations state that they should not be opened except by experienced personnel. In the fieldthey should only be cleaned by either blowing the detector through with high-pressure air or byvacuuming. Ideally they should be returned to Apollo for cleaning and recalibration.

There is no limit to the amount of ionisation smoke detectors that may be installed in any fireprotection system, however, there will be regulations for storage, depending on local standardsand legislation. In the UK up to 500 detectors may be stored in any premises, although there arestipulations on storage facilities if more than 100 detectors are stored in one building.

At the end of their recommended working life of ten years, ionisation detectors should be returnedto Apollo for safe disposal or disposed of in an otherwise locally approved and environmentally

safe manner.


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Optical Smoke DetectorsThe optical smoke detectors manufactured by Apollo have a chamber that incorporates an IR(infra-red) LED and a photo-diode. The components are located at an angle such that no lightemitted from the IR LED falls upon the photo-diode in clean air conditions.

Series 65 Optical Smoke DetectorsThe IR LED emits a burst of light every four seconds. When smoke particles enter the chamber, light

is scattered in all directions within the smoke chamber, some of this light will fall on the photo-diode. If enough light is seen by the photo-diode to indicate an alarm condition, the IR LED willemit a further two bursts of light at two second intervals. If the total amount of light sampled isgreater than that required to initiate an alarm condition, the detector will latch into its alarm state.

XP95 Optical Smoke DetectorsThe optics in the XP95 optical smoke detector are exactly the same as those in the Series 65. TheIR LED emits a burst of light every one second. The amount of light falling on the photo-diode isdirectly related to the smoke density and characteristics. This level is then converted into a valuethat is reported to the control panel.

This type of detector gives a good response to slow burning/low energy smouldering type fires

that emit visible smoke particles (>0.3 micron in size).Optical detectors can easily be cleaned in the field, again by blowing through the detector withhigh-pressure air or by vacuuming the device. They can also be opened by simply using a cross-headed screwdriver to undo screws in the lid. Once the lid is removed the optical chamber can becarefully unclipped and removed. Then a soft brush or detector duster aerosol could be used toremove any dust and debris in the chamber.

Once cleaned all devices should be re-tested using smoke to ensure they are in correct workingcondition.

Figure 2: Optical Smoke Chamber

In clean air With smoke

Photo-diode

Infra-red LED

Light beam

Diffused light beam

Smoke particle

A ollo Fire Detectors 1997/RHD


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Heat DetectorsOlder style rate-of-rise heat detectors manufactured by Apollo incorporate a pair of matchedthermistor beads. One of the thermistor beads is well insulated and the other is exposed to theambient air. The exposed thermistor responds quickly to changes in air temperature (its resistancefalls as the temperature increases). The other thermistor, being insulated, responds more slowly.When the ratio of resistances reaches a preset level, the detector latches into its alarm state. Thatdetermines the rate-of-rise response of the detector.

In the event that the temperature increases more slowly, there is never any great differencebetween the resistance of the thermistor beads. The detectors, however, incorporate a fixed valueresistor and when the ratio between the exposed thermistor and the insulated thermistor/ fixedresistor combination reach a preset level, the detector latches into alarm. That determines thefixed temperature response of the detector.

Now, conventional heat detectors are fitted with micro-controllers and use a single thermistorbead. Algorithms (mathematical formulas) are factory programmed to give a response to EN54 Pt5 classifications as shown in the table on page 12.

Note: analogue addressable heat detectors are fixed temperature devices and consequently

only incorporate one thermistor bead. The value reported by the detector to the panel is directlyproportional to the temperature at the thermistor.

Normal Conditions Rate-of-rise response Fixed temperature response

Thermistorpartiallysealed fromsurroundingair

Thermistorexposed to air

Fire detected on fastincrease of ambient

temperature

Fire detected on slowincrease of ambient

temperature

Note: Analogue addressable heat detectors use only a single thermistor

Ap ollo Fire Dete ct ors Limite d 1997/ RHD/JDR

Figure 3: Dual Thermistor Heat Detection


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Multisensor DetectorsThe multisensor detector has an optical sensor identical to that of the XP95 optical detector withan additional thermistor bead. The signals from the optical and temperature sensor elements areindependent and represent the smoke level and the air temperature in the vicinity of the detector.The detectors micro-controller processes the two signals to give a value that is reported to thecontrol panel.

Available in the XP95 and Discovery ranges, this type of detector is basically an optical smokedetector, so it will respond well to smouldering fires. The addition of a heat-sensing element allowsthe multisensor to give a response to fast-burning, flaming fires, which is comparable to that of anionisation detector.

Multisenor detectors are general purpose detectors that respond well to a wide range of fires.

Photo-diode

Infra-red LED

Thermistorexposed to air

+

Apollo Fire Detectors Limited 2001/JDR

Figure 4: Multisensor Detector

We have also introduced a conventional multi-sensor in the Orbis range. This uses a differentoptical chamber then that shown above but still uses a thermistor bead in combination. It willnot respond to temperature change alone however. It is essentially a thermally enhanced opticaldetector and is useful in areas where a flaming fire risk exists.


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CARBON MONOXIDE FIRE DETECTORS

Carbon Monoxide (CO) is a poisonous gas produced by combustion and a CO fire detector isused to indicate the outbreak of fire by sensing the level of CO in the air. The detector has anelectrochemical cell which senses CO, but not smoke or other combustion products. The cells donot require much power, so the detector can be made electrically compatible with ordinary smokeand heat detectors.

The electrochemical cell works like a battery: it is a simple two-electrode design and consistsof a semi-permeable diffusion membrane, a reservoir or acid electrolyte, a sensing electrodeand a counter electrode. CO diffusing into the cell reacts at the surface of the sensing electrodeproducing, as a by-product, a number of ions (H+) and electrons (e-). The ions travel throughthe acid electrolyte to the counter electrode whilst the negatively charged electrons travel tothe counter electrode via the external circuit. Combining the electrons and ions at the counterelectrode completes the reaction without any of the cells components being consumed. Theamount of electrons produced by the reaction is directly proportional to the amount of CO present,so measuring the current flowing through the external circuit is a basic gas monitor.

The life expectancy of the electrochemical cell in a CO fire detector is typically around seven years

in a clean, non-corrosive environment. The device can be returned to our service department forreplacement.

Carbon Monoxide fire detectors are a recent addition to the range of products available. Theprinciples of use are not fully established and the real value of CO fire detection is still beingdebated.

UK Standards & Guidelines:Recognised in BS 5839-1: 2002Product standard: LPS1265 (CO), LPS1275 (CO Heat)BFPSA Application Guidelines


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Selecting the Correct DeviceWhen selecting a detector for a particular area, the following points should be considered:

What is the risk of fire developing in this area?

Is a fire likely to be a rapidly-developing, high-energy type fire or a slowly developing,smouldering fire?

Under normal conditions, will there be high ambient levels of smoke or steam present?

Is the area a clean, dry environment or are there high levels of dust, dirt or moisture?

Is there likely to be a high concentration of cigarette smoke?

Are there any special risks?

Is there a high ambient temperature or significant variations in temperature?

It may be that one or any of the above conditions can occur infrequently. Even so, they do stillneed to be considered before selection.

Ionisation detectors are particularly sensitive to very small or invisible particles of smoke generatedby fast developing, high-energy type fires. It should always be remembered though that as thissmoke spreads and cools, the smoke particles tend to combine and become visible. For example,if smoke is spreading into an escape route from the fire source, the ionisation detector may not bethe best detector to protect the escape route.

Because they operate by effectively seeing smoke, optical detectors are better at detecting large,visible smoke particles usually generated by a slowly developing, smouldering type fire wheresmoke could become a major hazard before the fire properly develops.

Although there are two choices when it comes to selecting a smoke detector, it should beremembered that there is a good crossover of detection between the ionisation and opticaldetectors. There are, however, some circumstances where you may choose one type of detectorover another.

Heat detectors would only be used where it was impractical to use a smoke detector for whateverreason. Dirty environments, kitchens and boiler rooms are prime examples of where a heatdetector may be used.

Multi-sensors could be used as a replacement when ionisation detectors become undesirable. Theyare useful for detecting flaming combustion as well as smouldering fires. In fact, they are a goodgeneral purpose detector for most types of combustion.

CO detectors should only be used as a supplement to smoke detectors but in an L3 system theycould replace heat detectors in accommodation areas.

It should be understood that the aim is to achieve the best possible compromise betweenminimising the possibility of false alarms and giving the earliest warning of a real fire developing.


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In the conventional range of heat detectors from Apollo, there are many variants to choose from:

Series 65 A1R Heat Detector, part nos 55000-120/121/122The A1R heat detectors are the most sensitive of the range in terms of rate-of-rise and fixedtemperature response (5465C). Use an A1R instead of a smoke detector in locations wherehigh ambient ceiling temperatures and rapid variations are not expected. The sensitivity of thedetector must be considered if used in areas where rapid fluctuations of temperature are possible,

for instance, skylights, kitchens where oven doors might be opened, laundries where quantities ofsteam may be released.

Series 60 Grade 1 Heat Detector, part no 55000-100This detector has the same description as above except that the fixed temperature response is60C.

Series 60 Grade 2 Heat Detector, part no 55000-101Grade 2 detectors have a fixed temperature threshold of 65C but a less sensitive rate-of-riseresponse than a Grade 1 or A1R.

Series 65 BR Heat Detector, part no 55000-125/126/127The BR detectors have a fixed temperature response of 6985C and a less sensitive rate-of-rise

response than the A1R. Use where ambient ceiling temperatures are likely to be 4065C butwhere rapid changes are normal and should not trigger an alarm. Examples of such places arelaundry areas and steam rooms.

Series 60 Grade 3 Heat Detector, part no 55000-102This detector has the same description as above except that the fixed temperature response is75C.

Series 60 Range 1 Heat Detector, part no 55000-103This detector has a fixed temperature response of 80C and may be used where ambient ceilingtemperature of up to 55C are expected.

Series 65 CR Heat Detector, part no 55000-130/131/132CR detectors have a fixed temperature response of 84100C and may be used when ambientceiling temperatures of 5580C are expected, for instance, in boiler rooms, industrial kitchens andswimming pools. This detector still has a rate-of-rise response so will therefore still respond to arapid rise in ambient temperature although this will be less sensitive than in previous devices.

Series 60 Range 2 Heat Detector, part no 55000-104This detector has the same description as above except that the fixed temperature response is100C and may be used where ambient ceiling temperatures of 65C are expected.

Series 65 CS Heat Detector, part no 55000-135/136/137CS heat detectors also have a fixed temperature response of 84100C for use when ambient

ceiling temperatures are 5580C. This detector can be used in similar applications to the CRdetector except that this device has no rate-of-rise response it is essentially a fixed temperatureheat detector.


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ConventionalH

eatDetectorClassifi

cationComparisonChart

Series60Heat

Detectors

Series65Heat

Detectors

Orbis

HeatDetectors

ApplicationT

emperature

StaticResp

onse

Min

Max

Min

Max

Grade160C

BS5445-5

(55000-100)

ClassA1R57C

EN54-5:2000

(55000-122)

Cla

ssA1R57C

EN54-5:2000

(OR

B-HT-1-1001)

25C

50C

54C

65C

Grade265C

BS5445-5

(55000-101)

Cla

ssA2S61C

EN54-5:2000

(OR

B-HT-1-1002)

25C

50C

54C

70C

Grade375C

BS5445-5

(55000-102)

ClassBR75C

EN54-5:2000

(55000-127)

ClassBR75C

EN54-5:2000

(ORB-HT-1-1003)

40C

65C

69C

85C

Grade375C

BS5445-5

(55000-102)

ClassBR75C

EN54-5:2000

(55000-127)

ClassBS75C

EN54-5:2000

(OR

B-HT-1-1004)

40C

65C

69C

85C

Range180C

BS5445-5

(55000-103)

ClassCR90C

EN54-5:2000

(55000-132)

ClassCR90C

EN54-5:2000

(OR

B-HT-1-1005)

55C

80C

84C

100C

Range2100C

BS5445-5

(55000-104)

ClassCS90C

EN54-5:2000

(55000-137)

ClassCS90C

EN54-5:2000

(OR

B-HT-1-1006)

55C

80C

84C

100C

R=RateofRise

S=StaticResponse


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Please answer the following questions:

1. Which British Standard covers the code of practice for the installation of fire systems?

2. What three properties are required to generate a fire?

3. Name four detectable properties of combustion.

4. What type of fire does an ionisation device respond well to?

5. What products are associated with NRPB?

6. What type of smoke particles are easily detected using an optical device?

7. Give two examples of areas that may require the use of heat detectors.

8. Which two sensors are used in our multisensor detector?

9. What is the maximum area permissible for a single zone?

10. What type of detector would you use to protect the following:

a) Plant room

b) Corridor

c) Computer room

d) Warehouse (ceiling greater than 15m)

e) Student accommodationf) Office area

g) Chemical store (hazardous)

h) Small kitchen

i) Boiler room

j) Ceiling void greater then 800mm

Module 1: Detection Principles &Device Selection Test

pp2160 module 1 detection principles & device selection issue 3

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