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Mechanisms for successful water mistprotection systems
Louise Jackman & Kelvin Annable
Fire Safety Group, BRE Global
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Project Overview
Three year research programme
Funded byBRE Trust
Industry partners (insurance and system suppliers)
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Selected Application
Commercial Offices
Suitable fire hazard Primarily a property protection application
Insurers concerned about open plan areas
Sprinkler protection required over 30 m EN protocol
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Project Tasks
1. Review
2. Survey3. Experimental test programme
4. Generic framework
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Review - Standards
CEN/TS 14972
Office occupancies of Ordinary Hazard Group 1 FM Approval Standard 5560
Light hazard occupancies
IMO A.800
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Design Fire Database
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Survey
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Findings From Review and Survey
Lack of public domain data available for solid combustible
fires and open plan spaces Lack of public domain data available addressing the
influence of key water mist parameters
CEN office test protocol is a good approach but could beimproved (fuel loading, ignition scenario, repeatability)
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Single wood crib tests
21 simple demonstration tests
conducted Single wood crib
Tests in open conditions
6 x 6 m ceiling at 2.8 metres height(unless stated otherwise)
All tests with a single low pressurewater mist nozzle
Highly repeatable scenario to allowfor direct comparison between aseries of tests
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Single wood crib tests
Crib ignited at one end
Allowed to burn until firespread reached the middle ofthe crib
Water mist manuallyactivated
10 minute duration
Any remaining fire manuallyextinguished this provided
comparative fire damageassessment
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Findings single wood crib tests
The effect of nozzle spacing, that is, the position of the fire
relative to the nozzle:
The potential influence was clearly demonstrated:
With the crib directly beneath the nozzle the fire waseffectively suppressed and extinguished (no residualsmouldering) at the end of the 10 minute waterdischarge.
With the crib away from the nozzle at the maximum
spacing the fire was not suppressed and fire spread
along the length of the crib.
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Findings single wood crib tests
0 2 4 6 8 10 12 14
0
100
200
300
400
500
600
700
800
900
1000
Water applied
Temperature
(oC)
Time (minutes from ignition)
T1 - Crib fire directly under water mist nozzleT2 - Crib at nozzle maximum spacing (1.85 m away)
Directly beneath nozzle
At maximum spacing
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Findings single wood crib tests
The effect of reduced water
flow (from 24 l/min down to13 l/min):
The reduction in water flowrate resulted in significantly
reduced fire suppressioneffectiveness
24 l/min suppression 2minutes after water applied
13 l/min less suppression9 minutes after water applied
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Findings single wood crib tests
The effect of shielding:
Highly shielded fire; thewater mist was preventedfrom achieving effectivesuppression and stoppingfire spread.
Partially shielded fire;effective at preventingspread to exposed fueland a level of fire controlwithin the shielded portionof the fire.
Highly shielded
Partially shielded
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Findings single wood crib tests
The effect of ceiling height
(4.3 m and 5.5 m):
The fire suppression
effectiveness wascomparable with the samescenario at 2.8 m and the
influence of ceiling height
was considered to havehad limited influence, forthe tested scenarios.
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Findings single wood crib tests
The effect of ventilation (at
low level affecting both thefire and water dischargeprofile):
The crib fire initially struggledto take hold but then spread
quickly. The fire was not
effectively suppressed,particularly in comparison totesting in still air conditions.
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Findings single wood crib tests
The effect of ventilation (atmid level affecting thewater discharge profileonly):
The ventilation (of the order2 3 m/s) wasdemonstrated to have acritical influence on theeffectiveness of the water
mist system. The watermist discharge pattern wasseverely affected by theventilation.
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Findings compartment tests
The effects of a sealed compartment:
The beneficial influence of a sealedcompartment on the water mist systemsuppression effectiveness was clearlydemonstrated.
In open conditions the crib was notsuppressed (with the crib fire atmaximum spacing). For the equivalentscenario, but with a sealedcompartment, the fire was effectivelysuppressed and fire spread along thecrib prevented.
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Findings compartment tests
The effect of a compartment and ventilation:
The compartment, in combination with the ventilationarrangements tested, had a beneficial influence on the firesuppression effectiveness. Visual observations showed
re-circulating air currents containing water mist dropletsdrawn into or blown into the fire location.
However, the fire suppression was not as efficient as thetest results demonstrated for still air conditions. Asignificant amount of water mist droplets were blown outthe open doorway
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Findings compartment tests
The effect of a compartment and
ventilation with a significant fuelloading:
Baseline test conducted withsealed low pressure water mistwith no ventilation
Second test conducted with a low
pressure water mist with ventilation Third test conducted with a high
pressure water mist with ventilation
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Findings compartment tests
Baseline test, no ventilation, low
pressure water mist system:
Frangible glass bulb systemoperation after 2 minutes 48 seconds.
System demonstrated effective firesuppression on exposed surfaces buthighly shielded wood crib continuedto burn freely. Overall, the water mistwas effective at controlling the fire
and limiting fire spread.
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Findings compartment tests
Identical scenario but
with ventilation:
Velocity readings (taken at
various locations in theroom) ranged from 0.7 4 m/s).
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Findings compartment tests
Low pressure system - Thedevelopment of the fire was severelyaffected (slowed) by the air flows. Incombination, the temperature atwhich the frangible bulb actuatedwas much higher. There was areduction in water above thechipboard table and water mistdroplets blown out the open door.
However, the overall performanceand effectiveness of the system wascomparable to an equivalent testconducted in still air conditions.
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Findings compartment tests
High pressure system - Thedevelopment of the fire was slowed.The activation temperature (andtherefore time of operation) of themist nozzle and distributioncharacteristics of the mist dischargewere detrimentally influenced by theventilation. The water mist systemwas not effective at preventing firespread despite a level of fire controlbeing demonstrated. The overallperformance and effectiveness of thesystem was not clearly proven.
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Findings office scenario fire tests
BRE developed and
characterised officescenario:
Stylised fuel, highlyrepeatable, easily obtained,cost effective.
Fuel loading representative
of OH1, medium fire growthrate, with target items.
Tests under an open 6 x 6 m
ceiling at 5 m height0 2 4 6 8 10 12 14 16
0
500
1000
1500
2000
2500
3000
Manually
extinguishedCEN office
BRE office 2
HeatRelease
Rate(kW)
Time (minutes from ignition)
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Findings office scenario fire tests
Sprinkler test; LPCB approved K80pendent sprinklers used.
Scenario in the centre of 4 headson a 12 m2 spacing (5 mm/min).
The sprinkler system wassuccessful at extinguishing flamingabove the table and preventing anyfurther burning in the plywood walls.
Only a low level of burning in thetwo shielded wood cribs persisted.The fire was effectively suppressed.
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Findings office scenario fire tests Low pressure water mist test
Scenario in the centre of 4heads on a 6.25 m2 spacing(5 mm/min) at ~13 bar
Flaming above the table waseffectively suppressed but thewood cribs under the tableburnt freely for the duration.The water mist system
demonstrated effective firesuppression for the testedscenario
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Findings office scenario fire tests
High pressure water mist test
Scenario in the centre of 4 headson a 9 m2 spacing (2.8 mm/min) at~100 bar
The system significantly reducedtemperatures within the officescenario fire set-up compared to theunsuppressed test and although a
level of fire control wasdemonstrated the fire was not
effectively suppressed.
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Conclusions Nozzle spacing has been demonstrated to have a critical
influence on the fire suppressing effectiveness of a water
mist system (in certain tested conditions);
Nozzle water flow rate (and associated coverage) has alsobeen demonstrated to have a critical influence on the fire
suppressing effectiveness of a water mist system (incertain tested conditions);
Shielding (the prevention of direct water spray onto a fire
location) has clearly been demonstrated to preventeffective fire suppression (in certain tested openconditions);
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Conclusions Ceiling height has been demonstrated to be highly
significant with respect to automatic heat activated water
mist system response times;
The possible effects of ventilation have been clearlydemonstrated:
Ventilation can severely affect the fire growth rate(either significantly slow or speed up);
Ventilation can severely detrimentally affect the waterdistribution profile of water based suppression systems
(high pressure systems most, low pressure systemsand to a lesser extent sprinkler system discharges);
Ventilation has been demonstrated to have a criticalinfluence on the fire suppressing effectiveness of water
mist systems (in certain tested conditions);
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Conclusions Some possible benefits of a compartment on the fire
suppressing effectiveness of a water mist system have
been clearly demonstrated (in certain tested conditions);
Tests were conducted with industry provided low and highpressure water mist systems against the BRE developed
office scenario. The results, with one exception, were ofsome concern as effective fire suppression was notdemonstrated. Results indicate that the water mistsystems, as installed for testing, were not able to provide
the intended level of fire protection. Or, in terms of thedesign of the tested systems, the spacing betweennozzles was too great and the quantity of waterdischarged too low, to provide effective fire suppression.
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Conclusions
One test with an industry provided low pressure water mist
system effectively suppressed the BRE developed officefire scenario. This test was conducted at approximately 5mm/min, an equivalent water coverage to that required bya sprinkler system in accordance with the specifications of
BS EN 12845.
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Conclusions A fire test protocol for office occupancies of Ordinary
Hazard Group 1 has been developed and experimentally
tested. This protocol will be submitted to the relevanttechnical British Standards committee for potentialinclusion into British Standard Draft for Development 8489
Commercial and industrial water mist systems.
Overall, the work has provided valuable new informationon a number of the parameters influencing successfulwater mist systems
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Thank You
Any questions?
Louise Jackman & Kelvin Annable
Fire Safety Group BRE Global
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