Presentation Transcript

1. 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 RISK INSIGHT, STRATEGY AND CONTROL AUTHORITY Reducing insurable risk through research, advice and best practice
2. 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 making What makes a system ‘perform’? What makes a system ‘reliable’? What’s RISCAuthority doing to help? Watermist
3. Provision of finely divided water droplets, typically 200um Droplets created at higher pressures than traditional sprinkler systems, through small orifices Sometimes driven by compressed gas or HP pumps Generally described as a 2 - part action: Thermodynamic cooling during evaporation Oxygen reduction through steam displacement Operated as: Deluge systems Bulb Actuated * What is watermist?
4. ‘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 Factor Halcocarbon 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’ Why is watermist ‘different’?
5. Example modes of operation of 3 challenges 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
6. 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 So is it ‘gas – like’ or ‘sprinkler – like’?
7. How long the fire has been burning effects performance
8. Fire size effects performance
9. Ventilation effects performance
10. Watermist density effects performance
11. 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 Summary
12. 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. That’s all well and good but …
13. CONCLUSIONS A very special set of circumstances need to exist for water mist to operate effectively robustly reliably as an extinguishing or control system
14. Watermist Strengths 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 High heat output fuels Liquid fuels Hot environments Enclosed environments Direct application Environmental cooling Hidden fires (if large)
15. 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 Building regulations and codes which specify or reference active protection in England and Wales
16. What BS 9999 states about sprinkler protection ‘Other systems’ must be equivalent to Sprinklers: Performance & Reliability
17. 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 Perform?
18. 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 (1)?
19. 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); What makes sprinkler systems Reliable (2)?
20. And even then we still find problems albeit rarely….
21. Comparison of systems specifications Sprinkler systems 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 LPC Rules incorporating BS EN12845 Proven system design criteria Published equipment specifications (EN12259) Certificated equipment
22. Comparison of systemsInstallation control valves Sprinkler installation control valves – opens on demand Secured against tampering Water alarm gong Water mist control valves take a number of different forms but often solenoids with electronic activation
23. Comparison of systems Sprinkler systems Water mist systems No minimum orifice size ( orifice sizes can be <1mm) Sprinkler orifice size (8mm minimum)
24. Comparison of systemsTesting of water supplies Sprinkler system Water mist systems Not all water supplies can be tested; All water supplies tested At commissioning; During service.
25. Comparison of systemsDuration of water supplies Sprinkler systems Water mist systems Varies with design but often 20 minutes or les Protection provided for duration of water supply Ordinary Hazard – 60 minutes Wetting of fire load, providing a controlling influence even after water supply duration
26. Comparison of systemsWater application rate Sprinkler systems Water mist systems Varies depending on system supplier May be based on a single fire test designed or selected by the supplier Specified against hazard
27. “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- 1
28. “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 Comparative fire tests conducted in the UK by BRE on an Office fire load concluded- 2
29. 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! Watermist equivalency with Sprinklers?
30. 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 Why do we need questionnaires for watermist?
31. www.RISCAuthority.co.uk
32. 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 Why questionnaires and not guides?
33. 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 Common flaws and mistakes (General)
34. 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 Closing
35. 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. NFPA 750