Briefing Paper Characterising The Smoke Produced From .
www.bre.co.ukBriefing PaperCharacterising the smokeproduced from modern materialsand evaluating smoke detectorsRaman Chagger
01Characterising the smoke produced from modern materials and evaluating smoke detectorsContentsAbstract 02Introduction 02Background 03The current test fires 04Methodology 05Results 06Analysis 09Summary of results 11Conclusions and recommendations for further research 12References 12Acknowledgements 13
02AbstractIntroductionThe test fires that are used to assessionisation and optical smoke detectorswere developed in the 1980s, but thematerials now found in modern serviceenvironments have changed since then.There is now a greater use of plasticsand flame retardant foams in modernbuildings, but little information existson the response of detectors to smokegenerated by the burning or smoulderingof such materials.The object of this research project was to investigate the smoke profiles generated in fire testsspecified in the EN 54-7 (commercial) and EN 14604 (domestic) smoke detector standards, andcompare them with smoke produced from burning or smouldering materials commonly foundin today‘s service environment. The intention was to establish whether the current test fires areadequate for assessing smoke detector performance in a broad range of fires involving modernmaterials, and – if not – to make recommendations.Twelve approved smoke detectors(commercial and domestic) were installedin a fire test room on the ceiling andthe walls. Twenty-nine fire tests wereperformed using a variety of materialsin flaming and smouldering conditions.In tests that produced sufficient smoke,97.8% of devices responded with anappropriate alarm.It was confirmed that ionisation andoptical smoke detectors are attunedto detecting different types of fires.However, sufficient evidence was foundto demonstrate that these detectorsnevertheless respond appropriately toa broad range of fires, both within andbeyond the limits of the test fires currentlyused to assess them.The research work was conducted in two phases. The first comprised of a review to identify thematerials and burning conditions that would be used in Phase 2, during which fire tests wereconducted.
03Characterising the smoke produced from modern materials and evaluating smoke detectorsBackgroundBoth ionisation and optical smoke detectors are used in commercial anddomestic environments. They use different techniques to detect smoke,making them more attuned to detecting different types of fire.Ionisation detectors use a small radioactive source (americium-241)inside an ionisation chamber that contains charged electrodes. Thechamber is arranged to allow a flow of air from outside. As the air entersit becomes ionized, generating an electric current between the chargedelectrodes. When smoke particles pass into the chamber the ionsbecome attached to them and are carried away, leading to a reductionin the current. More ions are stripped away when there are many smallparticles, such as those generated during flaming fires. When a materialis smouldering it tends to produce fewer but larger particles than itdoes when in flames. As these cause less current reduction, ionisationdetectors are inherently less responsive to the large smoke particlesgenerated during smouldering fires.Optical smoke detectors typically use a smoke scatter chamber,which contains an LED source with a collimated lens that producesa beam. A photodiode is located at an angle to the beam. As smokeparticles enter the chamber they interrupt the beam and the light isscattered and detected by the photodiode. This results in a voltagethat can be used to determine an alarm condition. Optical detectorsrespond to smouldering fires very quickly, as the larger particlesgenerated cause more scattering. Optical scatter chambers are lesssensitive to small particles – and become progressively less sensitiveas the smoke particle size approaches the LED wavelength used.Therefore optical smoke detectors are slower at detecting the smallsmoke particles generated from flaming fires. These detectors areless likely to produce false alarms from cooking fumes and steamthan ionisation detectors.As both technologies contain inherent strengths and weaknesses,this research project aimed to determine whether ionisation detectorsperform poorly in certain types of smouldering fires, and if opticaldetectors are less responsive to certain types of flaming fires.
04Characterising the smoke produced from modern materials and evaluating smoke detectorsThe current test firesThe average smoke profiles produced from the four test fires areshown in Figure 1. The y-axis (m) represents the optical density(measured in dB/m) and indicates the quantities of larger particlesgenerated during smouldering fires. The x-axis (y) is a dimensionlessquantity that represents the amount of ionisation taking place andrepresents the number of smaller particles generated during flamingfires.Both EN 54-7 and EN 14604 use the same methodology to identifythe most challenging conditions under which to test smoke detectors.Physical tests conducted in a smoke tunnel are used to establish theorientations at which the detector is least sensitive, and to select thefour least sensitive detectors from a batch of twenty.During the fire tests the four worst performing samples are installedin the fire test room (as specified in the relevant standard) at theleast sensitive orientation on the ceiling or wall. Four fire tests arethen performed as follows: TF2: smouldering wood, TF3: glowingsmouldering cotton, TF4: flaming plastics (polyurethane) and TF5:flaming liquid (n-heptane) fire.The four test fires produce a broad range of smoke types with differentproperties. These are used to assess the smoke entry characteristics andthe sensitivity levels of smoke detectors. Materials such as plastics andflame retardant foams will generate smoke with different propertieswhen flaming and when smouldering – depending on the type ofsmouldering (e.g. near a radiant heat source or sustained contact withhot surface). The research aimed to establish whether smoke from suchfires was effectively covered by existing fire tests, and to assess theperformance of ionisation and optical detectors when responding tosmoke of this kind.The conditions in the fire test room are tightly controlled and theintention is to produce reproducible test TF41.6TF51.4FlamingPolyurethanem (dB/m)1.21.0Flamingheptane0.80.60.40.200123yFigure 1: Average m:y profiles of the four currently used test fires456
05Characterising the smoke produced from modern materials and evaluating smoke detectorsMethodologyDuring phase 1 papers were reviewed and many expertswere contacted to determine whether there were anyknown cases of detectors not responding to certaintypes of smoke. The data gathered during this exercisehelped to establish the test fires to be performed and thesupplementary measuring equipment to be used.The equipment specified in the smoke detector standards(thermocouples near the floor and in the arc, obscurationmeter and MIC in the arc) was used in the fire test room. Inaddition the following equipment was installed to gatherfurther data:11mThermocouple locationsCO Carbon monoxidemeasuring instrumentationF1, F2 Flow meters 1 & 2OBS Obscuration meterMIC Measuring IonisationChamberTest FireLocationCOF1OBSMICF2 Two flowmeters7m3m CO measuring equipment Secondary obscuration meterFigure 2: Location of measuring equipment in the fire test room Ten additional thermocouplesTwelve approved smoke detectors and smoke alarmdevices from undisclosed manufacturers were used inthe fire tests. These comprised of eight domestic smokealarm devices (four ionisation and four optical) with twoionisation and two optical devices being installed on thewalls and ceiling. Additionally, four commercial smokedetectors (two ionisation and two optical) were installedon the ceiling.To define end point of the tests, guidance was taken fromthe EN 54-7 and EN 14604 standards, which specify end oftest limits for smouldering and flaming fires that are m 2dB/m or y 6 9)Thermocouple locations:(1)-(4) as shown 1cm from ceiling(5) 4.5cm from ceiling(6) 8cm from ceiling(7) 11.5cm from ceiling(8) 15cm from ceiling(9) 10cm from floor(10) 30cm from floorThermocouple11mFigure 3: Location of the thermocouples in the fire test room11mDOMESTICCOMMERCIAL Ions1 Opticals2Test FireLocation60º7m3mDevices 1–8- Ceiling mountedDevices 9–12- Wall mounted8121134109Figure 4: Location of the detectors in the fire test room567
06Characterising the smoke produced from modern materials and evaluating smoke detectorsResultsTwenty-nine test fires were conductedincluding the four test fires specified in EN 54-7and EN 14604. Of these 11 were smoulderingfires, 16 were flaming fires and two startedoff smouldering and went on to becomeflaming fires (shown as S-F in the table right).The table right summarises the tests that wereconducted, the fuels that were used and themode of smoke production.All devices were periodically replaced, asexposure to the smoke from a number oftests could cause contamination in the smokechambers that could potentially affect theirresponse. The second column indicates whenall 12 were replaced with brand new devicesof the same model, i.e. at tests 1, 10 and 22.Table 1: The 29 tests conducted in the EN fire test roomTest no.Device setFuelMode of smokeproduction11 of 3TF2- Beech wood sticksSmouldering21 of 3TF4- Non flame retardant PUFlaming31 of 3TF5- N-heptane TolueneFlaming41 of 3TF8- Decalin (from ISO 7240-9)Flaming51 of 3TF3- Cotton wicksSmouldering61 of 3TF1- Wooden sticks (from ISO 7240-9)Flaming71 of 3Regular unleaded petrolFlaming81 of 3Premium unleaded petrolFlaming91 of 3MDFFlaming102 of 3TF2- Beech wood sticksSmouldering112 of 3PVC cableSmouldering122 of 3Flame retardant PU foamFlaming132 of 3Flame retardant PU foamSmouldering142 of 3Flame retardant PU foamSmouldering (radiant)152 of 3Sunflower oilS-F162 of 3NewspaperSmouldering172 of 3Bedding PolyesterSmouldering182 of 3Bedding PolyesterFlaming192 of 3Nylon (small)Flaming202 of 3Nylon (medium)Flaming212 of 3NylonSmouldering223 of 3Bedding PolyesterSmouldering233 of 3ABSFlaming243 of 3PolystyreneS-F253 of 3PolycarbonateFlaming263 of 3PolycarbonateFlaming273 of 3PolyethyleneFlaming283 of 3PolyethyleneFlaming293 of 3ABSSmoulderingUnless otherwise specified all smouldering fires were conducted in the sustained mode withthe fuel in contact with a hot surface that was increasing in temperature throughout the test.
Characterising the smoke produced from modern materials and evaluating smoke detectors10Test 24 demonstrates the difference inresponse between ionisation and opticaldetectors to a smouldering then flaming fire.At first the polystyrene fuel is smoulderingdue to the increasing temperature of thesteel plate on which it rests. This leads to all6 photoelectric detectors responding beforethe defined end of test for a smouldering fire(m 2 dB/m) is reached. When the temperatureof the polystyrene reaches ignition point(shown as S-F on the chart) the fuel combusts.Within a few seconds the first ionisationdetector responds and all ionisation detectorsare in alarm before the defined end of test fora flaming fire (y 6) is reached.m (dB/m) and 0350-2400450500550600650-2.5-7.5Time (sec)Figure 5: Test 9- MDF in flaming mode876m (dB/m) and yTest 9 demonstrates the rapid response of theionisation detectors (both commercial anddomestic) to the small particles generatedduring the flaming fire. The response fromthe opticals is slightly delayed until the fireincreases in size and the radiant heat leads tomore smouldering particles being producedfrom the MDF. All detectors respond beforethe defined end of test for a flaming fire (y 6)is reached.837.5Commercial CeilingDomestic CeilingDomestic Wall# Device numberCO (ppm)The results from two of these tests are shownin Figures 5 and 6 (right).570Commercial CeilingDomestic CeilingDomestic Wall# Device 00Time (sec)Figure 6: Test 24- Polystyrene first smouldering then flaming115012001250-10CO (ppm)07
08Characterising the smoke produced from modern materials and evaluating smoke detectorsFigure 7: Tests 1 & 10- Smouldering beech wood sticks (TF2) in the fire test roomFigure 8: Test 3- Flaming n-heptane fire (TF5) in the fire test room
09Characterising the smoke produced from modern materials and evaluating smoke detectorsAnalysisOf the 29 test fires conducted five (shownin Table 2) produced too little smoke(17 Polyester smouldering, 18 Polyesterflaming, 19 Nylon, 25 Poly-carbonate and27 Polyethylene); these were repeated withmore fuel.In this context too little smoke would beconsidered to be either well before m 2 dB/mor y 6 or if all devices that would be expectedto respond had not responded.Table 2: Tests that produced too little smokeTestTypeFinalm*Final y*Meanm/yNo. of device alarms17Polyester (S)000018Polyester (F)0.060.230.2715119Nylon (F)0.110.420.2126625Polycarbonate (F)0.120.440.2733627Polyethylene (F)0.381.580.20328* These values indicate the m and y levels achieved after the last device operated or when the test was abandoned.The results from the remaining 24 tests arearranged in order of increasing m:y and areshown in Table 3.Table 3: Tests that produced sufficient smokeSixteen of the 24 test fires (shaded in thetable) fall within the m/y limits specified bythe TF2-TF5 test fires from EN 54-7. Fromthese tests only two negative responses wererecorded with 190 positive responses.TestTypeFinalm*Finaly*Meanm/yNo. of device alarms6TF1 (F)1.2716.40.07941212FR PU (F)0.474.560.0938129MDF (F)1.188.10.14812For the four tests that had a high mean m/yratio, the detectors responded for all firesexcept for domestic wall ionisations 10 and12, which did not respond to test fire 13, anddomestic ceiling opticals 2 and 6 that did notrespond to test fire 29.20Nylon M (F)0.171.230.167972TF4 (F)1.327.710.19621216Paper (S F)0.170.620.1991127Petrol L (F)2.1910.720.2094123TF5 (F)1.78.070.2164128Petrol S (F)0.943.80.23081228Polyethylene L (F)1.515.360.2596114TF8 (F)0.93.290.26651226Polycarbonate L (F)0.351.140.2726125TF3 (S)2.085.270.34291115Oil (S,F)1.333.980.49111223ABS (F)2.664.140.5831211PVC (S)1.161.730.70631210TF2 #2 (S)1.531.660.82261224Polystyrene (S,F)5.587.670.84351214FR PU (S-R)1.671.590.8516121TF2 #1 (S)2.322.290.93841222Polyester (S)1.230.951.581221Nylon (S)2.481.51.671213FR PU (S-S)1.340.971.881029ABS (S)6.532.243.0410* These values indicate the m and y levels achieved after the last device operated or when the test was abandoned.
10Characterising the smoke produced from modern materials and evaluating smoke detectorsFor the four tests that had a low mean m/yratio the detectors responded for all firesexcept for five optical devices that did notrespond to test 20. This is most likely due tothe relatively small size of the fire, as the peakm and y values generated during this fire weresignificantly lower than the other three fires.Even though no statistical data was gatheredby repeating the same tests, the resultsdo provide evidence of the responsecharacteristics for the types of detectors(optical or ion) to a variety of smoke typesproduced in smouldering and flaming modes.TF2 (average)1.8PolyesterNylon1.6FR Polyurethane1.4m (dB/m)It is suspected that if enough smoke hadbeen generated during test fire 20 then all12 devices would have responded. Howeverthis result has not been qualified, so from theresults of the remaining 23 fires we effectivelyhave six no responses and 270 responses. Thisrepresents positive responses 97.8% of thetime. The six no responses are attributed to theinconsistent response of one particular type ofdetector and suspected contamination for theremaining ones.2.01.00.80.60.40.200–– To improve reproducibility between testlaboratories, the location at which thetemperature near the floor is measuredshould be more clearly specifiedin EN 54-7.0.5y11.5Figure 9: The four smouldering fires with m/y values outside the TF2 range1.2TF5 (average)m:y (dB/m)TF5 0.18Nylon 0.168MDF 0.148FR PU 0.094TF1 0.07941.00.8m (dB/m)Data gathered from the additional equipmentinstalled in the fire test room suggests thatthe limits specified in EN 54-7 in terms of theworking volume and temperature distributionare adequate and do not need to be refined.However, the following recommendations aremade:–– Assess whether the number of directionaldependence measurements should beincreased for domestic smoke detectorsdue to the asymmetrical design.ABSm:y (dB/m)TF2 1.22Polyester 1.58Nylon 1.67FR PU 1.88ABS 3.041.2NylonMDFFR PolyurethaneTF10.60.40.200123456yFigure 10: The 4 flaming fires with m/y values outside the TF5 range
11Characterising the smoke produced from modern materials and evaluating smoke detectorsSummary of resultsOf the 29 test fires, five were considered to be too small and had to berepeated with more fuel. Of the completed 24 test fires:–– 16 were found to be within the m/y range of smoke types boundedby TF2 and TF5;–– four smouldering fires were found to be beyond the (m/y) limits fora TF2;–– four flaming fires were found to be beyond the (m/y) limits for a TF5.The m/y ratio for the TF1 flaming fire was found to be the worst caseof all the flaming fires. This indicates that a defined fire exists for theflaming test fire limit assuming m/y is the appropriate measurement.For the smouldering tests carried out beyond the TF2 limit, no definedtest exists. The m/y ratio for the smouldering ABS fire (29) wassignificantly higher than the others.The test fires TF2-TF5 do cover most general purpose applications asa real fire is unlikely to involve only a single type of material. As morematerials with different smoke characteristics are involved in the fire thelikelihood of detection increases.However, it should be noted that smouldering fires can continue for along time with only one material being involved, potentially leading tothe production of toxic gases in fatal concentrations. An example of thiswould be bedding in contact with a heat source such as a lit cigarette. Inthis case an ionisation detector may not respond and therefore shouldnot be sited in locations where such a scenario is possible. In contrast aflaming fire will eventually produce sufficient heat that will radiate ontoother materials and lead to the production of smouldering smoke towhich the optical detectors would be expected to respond.Twelve smoke detectors, eight of which were installed on the ceilingand four on the wall, were exposed to the smoke from a variety of testfires and responded with a 97.8% pass rate.
12Characterising the smoke produced from modern materials and evaluating smoke detectorsConclusions andrecommendationsfor further researchReferencesThe aim of this research was to measure the smoke characteristics of anumber of test fires using modern materials, and assess them againstthe test fires specified in EN 54-7 and EN 14604.(1) EN 54-7: 2000 A1 June 2002 A2 July 2006. Fire detection &fire alarm systems Part 7: Smoke detectors – point detectors usingscattered light, transmitted light or ionization. European Committeefor Standardisation. Central Secretariat, Rue de Stassart 36, B-1050Brussels.The research has demonstrated that commercial and domesticapproved ionisation and optical smoke detectors respond to a broadrange of fires with m/y ratios within and beyond the fire test limits of EN54-7 and EN 14604.The fire tests specified in EN 54-7 and EN 14604 are considered to beappropriate and are sufficiently wide in terms of distribution of smokecharacteristics.Both ionisation and optical smoke detectors are attuned to detectingcertain types of fire. In order to ensure that the most appropriate typeof device is installed, guidance on the appropriate use of ionisationand optical smoke detectors should be sought from relevant codes ofpractice.Recommendations for further work–– Assessment of the performance of a variety of optical heatmulti-sensor detectors to some of the fires conducted during thisresearch programme.–– Research into a repeatable smouldering fire with an m/yratio 3.0 dB/m with a better m/y profile.–– Research into an alternate realistic flaming fire with anm/y ratio 0.1 dB/m such as flaming flame retardant poly-urethane.(2) EN 14604: 2005. Smoke alarm devices. European Committee forStandardisation. Central Secretariat, Rue de Stassart 36, B-1050Brussels.(3) ISO/TS 7240-9:2012(en) Fire detection and alarm systems — Part 9:Test fires for fire detectors.
13Characterising the smoke produced from modern materials and evaluating smoke detectorsAcknowledgementsThe author would like to thank the followingfor their voluntary contributions to thisresearch project:–– Gent by Honeywell–– Hochiki Europe (UK) Ltd–– Protec Fire Detection PLC–– Sprue Safety Products Ltd–– System Sensor Europe–– Tyco Fire Protection Products–– XtralisThe author would also like to thank theBRE Trust for the funding it provided for thisresearch project
Watford, HertsWD25 9XXTEW 44 (0)333 321 8811enquiries@bre.co.ukwww.bre.co.ukBRE TrustThe BRE Trust uses profits made by BRE Group tofund new research and education programmes,that will help it meet its goal of ‘building a betterworld together’.The BRE Trust is a registered charity in England & Wales:No. 1092193, and Scotland: No. SC039320.79216 Test Fires Briefing Paper BRE 2014BRE Trust
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