1	Using Water Mist as an Alternative to Sprinklers in Heritage Buildings NFPA 914 Workshop, September 2002
2	Outline Chronology of Water Mist Heritage Buildings and Performance Base Design Objectives – Ideal and Realistic A Heritage site – suitability of water mist Correcting Mist Conceptions Issues on a real project – National Gallery of Art Lessons learned
3	Chronology of Water Mist NFPA 750, Standard for Water Mist Fire Protection Systems Committee formed in 1993 – New Technology, New Standard Many interested parties: casual to vital Provided fire protection engineering basis for development Research Era 1990 to 1998 … Market Emergence (1995 to present …)
4	Chronology … NFPA 750, Standard for Water Mist Fire Protection Systems Committee formed in 1993 – New Technology, New Standard Research Era 1990 to 1998 (?) intense research – 1 st principles Water based fire suppression, efficiency, limits, opportunities Manufacturers’ R & D efforts still on-going Military special applications still on-going Market Emergence (1995 to present …) Commercial development of technology, invention,
5	Chronology … NFPA 750, Standard for Water Mist Fire Protection Systems Committee formed in 1993 – New Technology, New Standard Research Era 1990 to 1998 (?) intense research – 1 st principles Market Emergence (1995 to present …) Commercial development of technology, invention, Marine sector = sprinkler equivalence – rapid growth Other sectors = halon replacement – very slow growth Standards development (IMO, NFPA 750; CEN TC 191) Formalized Test Protocols
6	Chronology … Acceptance Era (2000 to Present) By End User - Growing By AHJ - Approvals getting easier Growth is uneven - Oil fields, Marine, Co-Generation well advanced Land-based, heritage, commercial, computer rooms Slow in the US – depends on AHJ Rapid in Europe – Every End User decides for themselves Engineering and Construction Era (2000 + …) Design & approval methods established Specifications, Design Drawings, Construction Supervision
7	Chronology … Acceptance Era (1997 to Present) Engineering and Construction Era (2000 + …) Specifications, Design Drawings, Construction Supervision Hydraulics; mixtures of gas and water; achieving duration; piston pumps; materials; techniques; trained installers Acceptance Testing Maintenance and Reliability Costs
8	Heritage Buildings and Contents Windsor Castle Structure, tapestries, paintings, furniture, draperies “Good thing we didn’t have sprinklers installed, imagine having water damage in addition to this fire damage …” (!) Norwegian Wood Stave Churches Unique structure - materials, Icons from 1000 AD Arson-vulnerable, remote, long response time, no water supply Russian National Library 8^th century illuminated manuscripts Basement vaults – access, smoke, flooding …
9	Reasons for Performance Based Design in Heritage Properties Protection objective is very high Irreplaceable structure and contents Damage tolerance is very low Prescriptive infrastructure not present Heritage Buildings are seldom “code-compliant” May be remote from electricity, water supply, & fire service Holistic approach – fire suppression system affects other safety measures, and vice versa Water mist systems require performance based design
10	Ideal Objectives for Water Mist Systems Control fire better than sprinklers Discharge less water than sprinklers Be less intrusive than sprinklers Require no additional effort to satisfy the AHJ Cost no more to design and install … Cost no more to maintain … Be at least as Reliable as sprinklers
11	Realistic Objectives for Water Mist Control fire better than sprinklers Based on actual, recent fire tests May be custom designed under consultation with End User to establish performance objective Cautions The IMO or FM Test Protocol Pass/Fail criteria may not be what you want or need Sales enthusiasts will tell you “this system is FM approved” … (therefore can be applied to any hazard without further thought)
12	Realistic Objectives for Water Mist Discharge less water than sprinklers 20 to 40 percent of standard sprinkler discharge
13	Discharge Less Water
14	Discharge Less Water Than Sprinklers Water damage will be greatly reduced but not eliminated
15	Realistic Objectives for Water Mist Be less intrusive than sprinklers Smaller diameter pipe, mains and risers Attractive nozzles But Less choice than sprinklers for concealed nozzles Additional care in hanging, closer hanger spacing, may be more intrusive
16	Realistic Objectives for Water Mist Require no additional effort to satisfy the AHJ Require substantial effort to convince a reluctant AHJ Listings are not general enough Imperfect match between test protocols and real applications requires interpretation by knowledgeable persons … At best, organization acts as its own AHJ At worst, AHJ accepts without question (Europe)…
17	Realistic Objectives for Water Mist Cost no more to design and install … Depends: costs ~ 3 to 4 times cost of standard sprinklers New technology, equipment, - few contractors with necessary expertise In some circumstances, water mist can cost no more than sprinklers because of Less water storage Smaller pipe sizes, field labor No alternative (halon replacement)
18	Realistic Objectives for Water Mist Cost no more to maintain … Not yet – sole source maintenance contracts Maintenance procedures not in NFPA 750 or 25 Many types of systems, require proprietary expertise More electrical components New, unproven mechanical components
19	Realistic Objectives for Water Mist Reliability (equal to) sprinklers Reliability = will act when it needs to, no unwanted releases More complex equipment – more opportunity for errors or lapses in maintenance; no accumulated experience to rely on. Must achieve equivalent Reliability - but unknown For innovative system for Eurotunnel HGV trains, Eurotunnel required “failure modes and effects analysis” More such analysis is needed
20	Balance Fire control equal to or better than sprinklers Discharge less water than sprinklers Less intrusive than sprinklers
21	Balance Fire control equal to or better than sprinklers Discharge less water than sprinklers Less intrusive than sprinklers
22	Comparison of options Remote Heritage Site Several Separate Buildings No Power, No water
23	Potential Systems
24	Sprinkler solution Elevated tank (10 – 20,000 gallons) Underground, 3-ft bury Not allowed to dig … !
25	Stand-alone systems in each building …
26	Stand-alone systems in each building …
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28	GPU – Gas Driven Pump Unit
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30	Correcting Mist Conceptions “Water mist is a “total-flooding” agent” Sometimes, but seldom with class A fires Extinguish by O₂ depletion is true for machinery spaces Water droplets evaporate, turn to water vapor, and push the oxygen out of the compartment
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32	Correcting Mist Conceptions In Heritage buildings, galleries, public spaces, or storage spaces involving Class A fires Fuel Wetting, not total flooding, is the primary mechanism of extinguishing fire Tolerance for “larger” fires needed for total flooding mechanism to work is lowest in cultural properties Cooling of hot gases reduces buoyancy & smoke spread That means you don’t have to have air-tight compartment, Can tolerate large openings Can use individually thermally activated nozzles instead of full compartment deluge
33	Correcting Mist Conceptions “Water mist is more likely to damage oil paintings than sprinkler sprays, with larger water droplets” Basis: steam temperature > 100 deg C, will do more damage than liquid phase water drops. In a machinery compartment, average temperatures ~ 60 - 70 deg C BUT In a gallery setting, average temperature will be closer to 25 - 35 deg C, and the water vapor concentration < 5 % Water mist cools more than sprinkler spray So, water mist is not more likely to cause damage If the fire is large enough to create absolute humidity > 20% and temperatures > 35 deg C, worry about the fire, not the water vapor.
34	Correcting Mist Conceptions Water mist will ‘scrub’ smoke Water mist equipment manufacturers are claiming exaggerated benefits of smoke scrubbing “Water mist will scrub smoke and save artwork” “Smoke scrubbing will reduce damage to electronics” “Smoke scrubbing will improve exiting safety” “Smoke scrubbing will make smokey air breathable” (uncritical acceptance of these claims in Europe …)
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36	Smoke Scrubbing by Water Mist Industrial smoke scrubbing with water sprays Industrial scrubbers HEPA filter protection Comparable water mist systems for smoke scrubbing Computer room sub-floor system Critique of overstatements of scrubbing benefits Soot removal and visibility benefit Reduced corrosivity of smoke Reduced toxicity
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40	Critique: soot removal and visibility benefit Comment soot is washed out, it is evident in the runoff (but probably less than 25 % and extremely variable) changes in optical density are measurable (50 %), but highly variable & improvement not enough to go from “Unsafe” to “Safe” conditions Acidity and toxicity not altered
41	Benefits of Water Mist A better expression of the benefit of water mist with regard to smoke hazard management is that the water mist reduces the quantity of smoke generated by suppressing the fire reduces the temperature and buoyancy, hence smoke spread reduces the temperature and the threat to life or thermal damage to sensitive property
42	Split Personality – Proponent / Conscience Enthusiasm for Water Mist Systems “Designer sprays” achieve specific objectives at much higher levels of efficiency in use of water than sprinklers Freedom to use new technology allows unprecedented levels of control, logic, programming, intelligence in systems design Conscience of the Industry (or pain in the neck) Challenge overstatements of performance Eliminate careless, imprecise and incorrect engineering in factors such as Hydraulic performance, Duration, Capacity, Corrosion, Reliability Clarify the intent and substance of NFPA 750
43	Issues for Heritage Applications National Gallery of Art, Washington Sculpture Galleries Combustible ceiling, Combustible walls – Threat to rest of the Gallery Preaction system, pumped supply, engineered system NGA able to act as AHJ – required courage and commitment National Gallery of Art - Architect - Mechanical Engineering Firm - Hughes Associates (fire engineering) - Manufacturer (equipment) - Installer
44	Issues for Heritage Applications Biggest Problems Steep learning curve for traditional sprinkler contractor working with new materials, new techniques Transfer of knowledge from specialist manufacturer to contractor Costs high for Engineering, Contracting, Construction supervision Coordination between the water mist system hardware and the fire detection/activation contracts
45	National Gallery of Art, Washington Lessons Learned Skill, experience of installer is critical; one has acquired the experience; no-one would want to start over with a “green” contractor. Even performing the hydraulic calculations unexpectedly difficult Unexpected difficulties with confined spaces, tightening fittings Labor for hanging the high pressure tubing in difficult spaces was 3 times or more than the contractor’s original estimates
46	Engineering of Water Mist Systems An FPE should be involved in the design, supervision and field evaluation of Water Mist system Installations Vendors are good, but they are not always thinking about the End-User’s real needs Review of installations after completion revealed Systems do not comply with NFPA 750 Fire test protocol as basis for design not matched to actual hazard Capacity of nitrogen inadequate, hence Duration of protection inadequate Hydraulic calculations not done, or not done properly Long term maintenance issues
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