water mist systems

8/9/2019 Water Mist Systems

1/36

Mechanisms for successful water mistprotection systems

Louise Jackman & Kelvin Annable

Fire Safety Group, BRE Global


2/36

Project Overview

Three year research programme

Funded byBRE Trust

Industry partners (insurance and system suppliers)


3/36

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


4/36

Project Tasks

1. Review

2. Survey3. Experimental test programme

4. Generic framework


5/36

Review - Standards

CEN/TS 14972

Office occupancies of Ordinary Hazard Group 1 FM Approval Standard 5560

Light hazard occupancies

IMO A.800


6/36


7/36

Design Fire Database


8/36

Survey


9/36

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)


10/36

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


11/36

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


12/36

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.


13/36


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


14/36


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


15/36


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


16/36


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.


17/36


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.


18/36


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.


19/36


20/36

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.


21/36


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


22/36


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


23/36


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.


24/36


Identical scenario but

with ventilation:

Velocity readings (taken at

various locations in theroom) ranged from 0.7 4 m/s).


25/36


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.


26/36


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.


27/36

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)


28/36


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.


29/36

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


30/36


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.


31/36

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);


32/36

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);


33/36

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.


34/36

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.


35/36

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


36/36

Thank You

Any questions?

Louise Jackman & Kelvin Annable

Fire Safety Group BRE Global

water mist systems

Documents