RISK INSIGHT, STRATEGY AND CONTROL AUTHORITY Reducing insurable risk through research, advice and...

RISK INSIGHT, STRATEGY AND CONTROL AUTHORITY

Reducing insurable risk through research, advice and best practice

Watermist for Risk Control

(Why it’s not as simple as all that!)RISCAuthority Seminar 2012

Dr Jim Glockling

Technical Director,

Fire Protection Association

Director RISCAuthority



1



Watermist

• What is watermist?

• Why is it ‘different’ to other forms of suppression?

• Why will it always be complicated to specify and

prove?

• Where equivalency is asked for what comparisons

need makingo What makes a system ‘perform’?o What makes a system ‘reliable’?

• What’s RISCAuthority doing to help?

2



What is watermist?

1. Provision of finely divided water droplets, typically 200um

2. Droplets created at higher pressures than traditional sprinkler systems, through small orifices

3. Sometimes driven by compressed gas or HP pumps4. Generally described as a 2 - part action:

• Thermodynamic cooling during evaporation• Oxygen reduction through steam displacement

5. Operated as:• Deluge systems• Bulb Actuated *

3



Why is watermist ‘different’?

‘Guidance’ of the type given for sprinkler and gaseous systems is too difficult to give

Sprinklers mm/min water for each ‘Hazard Category’Inert gaseous systems %O2 for hazard (O2 index) +

Safety FactorHalcocarbon gas systems %gas for hazard (cup burner test)

+ SF

Watermist more problematic since there are many modes of operation and the properties of the fire and the enclosure may determine which one, if any, occurs.

There is no concept of ‘Safety Factor’

4



Example modes of operation of 3 challenges

5

O2 depletion Foam delivery Surface cooling

Key parameters: Fire size, Compartment size, Compartment height, Compartment Ventilation, Amount of clutter, Nozzle location, Use of foam, Temperature of equipment



So is it ‘gas – like’ or ‘sprinkler – like’?

The safest bet is to assume:

• It is ‘gas – like’ in that it requires a well sealed enclosure

• It is ‘sprinkler – like’ in that it must have direct access to the fire

Unless someone can convince you through appropriate testing to think otherwise.

Retailers will often vary the answer to suit the argument:•Use in warehousing•Use in cluttered environments•Where poor distribution has been established

6



-600 -480 -360 -240 -120 0 120 240 360 480 6000

50

100

150

200

250

300

350

Run 2 - 7.5 minutes pre-burn Run 10 - 3 minutes pre-burn

Comparison mean enclosure temperature

Tem

pera

ture

(C

)

Time (s)

-600 -480 -360 -240 -120 0 120 240 360 480 6004

6

8

10

12

14

16

18

20

22

Comparison oxygen concentrations

Oxy

ge

n (

%)

Time (s)

Run 2 - Low level - 7.5 minutes pre-burn Run 2 - High level - 7.5 minutes pre-burn Run 10 - Low level - 3 minutes pre-burn Run 10 - High level - 3 minutes pre-burn

Oxygen concentrationsprior to system operation

(%)Run

number

Pre-burn time

(minutes)

Mean enclosuretemperature

prior to systemoperation

(C)High Low

Extinguishingtime

(seconds)

2 7 ½ 295 8.34 15.19 10

10 3 258 10.04 17.23 45

Table 1 – Influence of pre-burn times on extinguishment of the large spray fire

How long the fire has been burning effects performance



-240 -180 -120 -60 0 60 120 180 240 300 3600

20

40

60

80

100

120

140

160

180

200

Run 38 - Small spray fire Run 39 - Large spray fire


Tem

pera

ture

(C

)

Time (s)

-240 -180 -120 -60 0 60 120 180 240 300 36015

16

17

18

19

20

21

22


Oxy

gen

(%)

Time (s)

Run 38 - Low level - Small spray fire Run 38 - High level - Small spray fire Run 39 - Low level - Large spray fire Run 39 - High level - Large spray fire

Oxygenconcentrations priorto system operation

(%)

Runnumber

Fire size



(C) High Low

Extinguishingtime

(seconds)

38 Small spray 129 17.82 20.45 Not extinguished

39 Large spray 175 15.75 20.81 31

Table 1 – Influence of fire size upon extinguishment by Fine Water Spray

Fire size effects performance



-360 -240 -120 0 120 240 360 4800

20

40

60

80

100

120

140

160

180

200

220

240

260

Run 25 - 2 vent panels removed Run 39 - 4 vent panels removed Run 47 - 8 vent panels removed Run 24 - 8 vent panels removed


Tem

pera

ture

(C

)

Time (s)

-360 -240 -120 0 120 240 360 48010

12

14

16

18

20

22


Oxy

gen

(%)

Time (s)

Run 25 - Low level - 2 panels removed Run 25 - High level - 2 panels removed Run 39 - Low level - 4 panels removed Run 39 - High level - 4 panels removed Run 47 - Low level - 8 panels removed Run 47 - High level - 8 panels removed Run 24 - Low level - 8 panels removed Run 24 - High level - 8 panels removed


(%)

Runnumber

Vent panelsremoved



(C) High Low

Extinguishingtime

(seconds)

25 2 238 11.64 17.08 14

39 4 175 15.75 20.81 27

47 6 165 17.65 20.84 35

24 8 147 18.06 20.83 Not extinguished

Table 1 – Influence of ventilation on extinguishment of the large spray fire

Ventilation effects performance




(%)Run Nozzles Fire size

Mean enclosuretemperature prior

to systemoperation

(C) High Low

Extinguishingtime

(seconds)

11 4 Small spray 131 17.83 19.88 Not extinguished

14 6 Small spray 125 18.00 19.53 52

10 4 Large spray 258 10.04 17.23 45

15 6 Large spray 241 11.33 17.72 17

Table 1 – Summary data of tests using different numbers of nozzles

Watermist density effects performance



Summary

• Fires that have been burning for LONGER, are hotter, and have less oxygen available and may therefore be EASIER to extinguish

• Fires that are BIGGER, are hotter, and have less oxygen available and may therefore be EASIER to extinguish

• Fires with LESS VENTILATION cannot replace the oxygen displaced by steam as quickly and may therefore be EASIER to extinguish

• Fires subjected to MORE DROPLETS can produce steam more rapidly which may BENEFIT extinguishment

11



That’s all well and good but …

LONGER, BIGGER, LESS VENTILATION, MORE DROPLETS

may mean different things in different sized enclosures with different size fires. The challenge of:

• Physically SMALL fire in a physically BIG enclosure• Physically LARGE fire in a physically SMALL enclosure• Physically LARGE fire in a physically BIG enclosure• Physically SMALL fire in a physically SMALL enclosure

Will be different, and what’s more, as the fire becomes affected, will change in size and alter dynamically ….. cycling of fires is not uncommon.

12



A very special set of circumstances need to exist for water mist to operate

effectively robustly reliably

as an extinguishing or control system

CONCLUSIONS



Watermist

Strengths• High heat output fuels• Liquid fuels• Hot environments• Enclosed

environments• Direct application• Environmental cooling• Hidden fires (if large)

Weaknesses• Ventilated spaces• High ceiling heights• Small fires• Hot surfaces

(sustained ignition sources)

• Deep seated fires• Hidden fires (if small)• Little residual benefit

one water exhausted• Class A fuels 14



Building regulations and codes which specify or reference active protection in England and Wales

• The Building Regulations 2000: Approved Document B

• Compensatory feature for variation from AD ‘B’

• BS 9999:2008 Code of practice for fire safety in the design, management and use of building

• Fitting of sprinkler systems allows adjustment of the risk profile and permits:

• Reduction in the fire growth rate;

• Allowing larger travel distances;

• Larger compartments;

• Reduced fire resistance periods;

• Other provisions recommended in the standard

• BS 7974 Application of fire safety engineering principles to the design of buildings



What BS 9999 states about sprinkler protection

‘Other systems’ must be equivalent to Sprinklers: Performance & Reliability



What makes sprinkler systems Perform?

• Historical record of over 100 years with continuous development and improvement

• Substantial number of fire tests in support of design and development for

• Ordinary Hazard; and • High Hazard risks

• Proven equipment reliability;

• Proven installation standards which create a level playing field in a competitive marketplace.



What makes sprinkler systems Reliable (1)?Reliability of sprinkler systems and equipment was problematic in the early years of sprinkler protection. Most problems have been resolved by:

• Specifications for equipment;

• Specified clearances between moving valve parts

• Sprinkler orifice minimum size limits (8mm ND)

• Continuous refinement of detailed installation design specification;

• Robust definition of hazard vs. design requirements

• Robust water supply design (Security)

• Duplication



What makes sprinkler systems Reliable (2)?

• Testing and certification of hardware;

• Certification of installing companies

• Auditing of installing companies and their work

• Rigorous inspection & testing of installed system;• Acceptance tests and inspections including flow tests• Weekly and periodic testing and inspections;• Checking installation control valve function;

• Pump testing (if pumps are used);



And even then we still find problems albeit rarely….



Comparison of systems specifications

Sprinkler systems

• LPC Rules incorporating BS EN12845

• Proven system design criteria

• Published equipment specifications (EN12259)

• Certificated equipment

Water mist system

• No UK or European standard (BS DD/CEN TS)

• Few proven system design criteria mostly for specialised applications

• No published UK or European equipment specifications

• Few certificated products

• NFPA 750



Comparison of systemsInstallation control valves

Sprinkler installation control valves – opens on demandSecured against tampering

Water alarm gong

Water mist control valves take a number of different forms but often solenoids with electronic activation



Comparison of systems

Sprinkler systems

• Sprinkler orifice size (8mm minimum)

Water mist systems• No minimum orifice

size( orifice sizes can be

<1mm)



Comparison of systemsTesting of water supplies

Sprinkler system• All water supplies

tested• At commissioning;• During service.

Water mist systems• Not all water supplies

can be tested;



Comparison of systemsDuration of water supplies

Sprinkler systems• Ordinary Hazard – 60

minutes

• Wetting of fire load, providing a controlling influence even after water supply duration

Water mist systems• Varies with design but

often 20 minutes or les

• Protection provided for duration of water supply



Comparison of systemsWater application rate

Sprinkler systems• Specified against

hazard

Water mist systems• Varies depending on

system supplier

• May be based on a single fire test designed or selected by the supplier



Comparative fire tests conducted in the UK by BRE on an Office fire load concluded- 1

“Tests were conducted with industry providing low and high pressure water mist systems against the BRE developed office scenario. The results, with one exception, were of some concern as effective fire suppression was not demonstrated.

Results indicate that the water mist systems, as installed for testing, were not able to provide the intended level of fire protection. Or, in terms of the design of the tested systems, the spacing between nozzles was too great and the quantity of water discharged too low, to provide effective fire suppression.”



Comparative fire tests conducted in the UK by BRE on an Office fire load concluded- 2

“One test with an industry provided low pressure water mist system effectively suppressed the BRE developed office fire scenario. This test was conducted at approximately 5mm/min, an equivalent water coverage to that required by a sprinkler system in accordance with the specifications of BS EN 12845.”

Reference: http://www.brebookshop.com/details.jsp?id=326685



Watermist equivalency with Sprinklers?

• Reliability?• Performance?

There is little by way of codes or standards to dictate that watermist systems will have many of the features that we know make Sprinkler Systems effective for the long term protection of property and business:

It will need to be specified separately!

29



Why do we need questionnaires for watermist?

• Repeated calls from insurers for guidance, especially when proposed in place of sprinkler systems

• A need for RISCAuthority to promote new technologies to where they can provide most benefit for business and property protection- in the right places watermist is the BEST option.

• To allow the designer/specifier to demonstrate to the purchasers/insurer that a full and appropriate job has been/will be done in the design and implementation of the system

30



www.RISCAuthority.co.uk

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Why questionnaires and not guides?

• Watermist function is complex

• There are no appropriate standards or certification schemes to rely on

• To describe for every eventuality is impossible

• Checking that all design elements:• have been considered• usual risk control logic has been followed• properly recorded• and are ‘owned’is the only practical approach

32



Common flaws and mistakes (General)• Design intention is not properly understood (i.e. property protection vs.

LS)• Risk never properly investigated and/or understood• System design never validated against appropriate risk (marine)• System design does not consider all ‘modes’ of operation of the

equipment it is protecting• Very short water supply durations in comparison with shut down &

control of ignition sources• Activation not interlocked with:

• Power / fuel / ignition sources• Ventilation / Conveyancing equipment

• Inappropriate detection in the context of suppression system’s / risk’s needs

• Insufficient control of ventilation• Insufficient guidance, training, and manuals• Inappropriate referencing of sprinkler equivalency• No overall ownership

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Closing

• Questionnaires ONLY ask details of the steps that MUST be taken in the provision of an effective watermist response

• Difficultly to complete may indicate that all the bases have not been covered and should serve as a warning

• The intention is to develop further questionnaires for gaseous extinguishing systems

More information at the poster exhibition outside.

END

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NFPA 750

• Scope. This standard contains the minimum requirements for the design, installation, maintenance, and testing of water mist fire protection systems. This standard does not provide definitive fire performance criteria, nor does it offer specific guidance on how to design a system to control, suppress, or extinguish a fire. Reliance is placed on the procurement and installation of listed water mist equipment or systems that have demonstrated performance in fire tests as part of a listing process.

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