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Fire Dynamics II. Lecture # 9 Room-fire Dynamics Jim Mehaffey 82.583. Room-fire Dynamics Outline Introduction Fire development: experimental findings Impact of ventilation, boundary type and fuel load Fire growth: combustible linings

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Fire Dynamics II


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    1. Fire Dynamics II Lecture # 9 Room-fire Dynamics Jim Mehaffey 82.583 Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    2. Room-fire Dynamics Outline • Introduction • Fire development: experimental findings • Impact of ventilation, boundary type and fuel load • Fire growth: combustible linings • Characterize flashover: Transition from burning of one or a few objects to full room involvement Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    3. Introduction Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    4. Upper Layer Temperature During an Enclosure Fire Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    5. Contribution of Room Linings to Fire Growth • First item ignited may be combustible room linings rather than contents • Fire spreads up the wall (or corner) and spreads along upper part of walls (and under the ceiling if also combustible): wind-aided spread • A hot upper layer is generated which radiates energy to portions of the upper wall not yet burning • Opposed flow flame-spread increases rate of heat release and temperature of upper layer which, in turn, causes faster flame spread • Upper layer may become hot enough for flashover Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    6. Flashover • Transition from burning of one or a few objects to full room involvement Statistics • In non-sprinklered residential buildings 22 - 25% of fires proceed to flashover Room Size • For small rooms (~100 m3) important to determine when (if) flashover occurs (life safety) • For large rooms (~1,000 m3) time to flashover can be long, but a localized pre-flashover fire may be sufficiently severe to cause local structural damage Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    7. Flashover Criteria • Flashover has been defined as occurring when: 1. Fire appears (visually) to undergo rapid transition from localised burning to full-room involvement 2. Crumbled paper placed on floor is ignited 3. Flames emerge from the opening 4. Hot layer temperature reaches 500-600°C 5. Radiant heat flux at floor reaches 20 kW m-2 • Experimental studies have employed criteria 1 to 5 • Theoretical studies employ criteria 4 & 5 Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    8. Experiments: Mehaffey & Harmathy, 1985 • 32 room fire experiments • Fuel: wooden cribs • Fuel load: simulated hotel & office rooms • Room Dimensions • Floor: 2.4 m x 3.6 m • Ceiling height: 2.4 m • Ventilation opening • Open throughout test • Purpose of experiments • Assess thermal response of room boundaries exposed to post-flashover fires Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    9. Impact of boundary (thermal properties) Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    10. Impact of boundary (thermal properties) • Fuel: wooden cribs: 15 kg m-2 (hotel) • Window: area = 9% area of floor • b =0.7 m; h =1.2 m; = 0.92 m5/2 • Post-flashover fire: ventilation controlled • rate of heat release = 970 kW ~ 1 MW • . . . . “Standard fire” CAN4-S101 (ASTM E119) Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    11. Impact of size of openings Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    12. Impact of size of openings • Fuel: wooden cribs: 27 kg m-2 (office) • Thermal inertia of room boundaries • = 666 J m-2 s-1/2 K-1 • kc = 0.444 kJ2 m-4 s-1 K-2 • Post-flashover fire: ventilation controlled • . . . . “Standard fire” CAN4-S101 (ASTM E119) Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    13. Experimental Results: Post-flashover Fires (SFPE Handbook) • Floor area = 29 m2 • Fuel load: wooden cribs • First two tests: Fuel-surface controlled • Last three tests: Ventilation controlled Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    14. Experimental Results: Post-flashover Fires (1) • Largest single loss: Note % lost  as vent area  • Significant loss: Note % lost  as vent area  • Small loss: Note % lost  as vent area  Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    15. Pitt Meadows, B.C. - Video October 19-24, 1996 • 1-storey wood-frame apartment building to be demolished • Local fire departments & IAAI plan full-scale fire tests & training program • UBC / Forintek invited to monitor tests • Video - visual display of flashover - role of ventilation in flashover Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    16. Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    17. Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    18. Maximum Possible Heat Release Rate • One pane open: b = 0.6 m and h = 1.33 m • Window broken: b = 2.7 m and h = 1.33 m Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    19. Pitt Meadows, B.C. - Video October 19-24, 1996 • One window pane open at beginning of test • Appears flashover will not occur as not enough ventilation (air supply) • Firefighters break rest of window glazing • Flashover occurs quickly thereafter Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    20. Temperature Profile in Living Room Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    21. Temperature Profile in Bedroom Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    22. Room Fire Test - Apparatus • ISO 9705 “Fire tests: Full scale room fire tests for surface products” • Contribution of room linings to fire growth (flashover) Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    23. Room Fire Test - Procedure • Line walls and ceiling with product • Burner in back corner • First 10 min: = 100 kW (large wastepaper basket) • Last 10 min: = 300 kW (small upholstered chair) • Observe time to flashover • Room experiences flashover when  1,000 kW Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    24. Room Fire Test - Results Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    25. CAN/ULC- S102: Red Oak and Plywood • At (red oak) = 43.0 m min  FSR (red oak) = 100 • At (plywood) = 47.2 m min  FSR (plywood) = 135 Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    26. CAN/ULC-S102: Gypsum Board • At (gypsum board) = A1 + A2 = 8.0 m min  FSR (gypsum board) = 15 Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    27. CAN/ULC- S102: Polyurethane Foam Insulation • FSR (PU foam insulation) = 427 (d/t) or 74 (At) Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    28. Room Fire Test - Video • Test follows ISO 9705 • Walls & ceiling: wooden panelling • Time to flashover  3:00 min Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    29. Simulation of Rhode Island Fire • NFSA = National Fire Sprinkler Association • Simulate the stage area • dimensions and layout approximately replicated • Foamed plastic acoustic insulation glued to plywood on wall and ceiling • propylene oxide polyol (not PU foam insulation?) • thickness = 75 mm (3”) • density = 16 - 20 kg m-3 (1-1.25 lb ft-3) • Ignition simulated ignition from pyrotechnics • Would sprinklers have helped? Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    30. Simulation of Rhode Island Fire - Video • Demonstrates rapid ignition and flame spread over exposed foamed plastic insulation Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    31. Kemano: Fire in Basement Recreation Room • Room dimensions: 3.25 m x 3.44 m x 2.2 m (height) • Walls: 2 gypsum board // 2 (6 mm) wood panelling • Ceiling: gypsum board • Floor: carpet over concrete • Furnishings: couch / coffee table / TV on wood desk • Ventilation: no window / hollow-core wood door closed Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    32. Temperatures in Basement Fire • Temperature predictions from Lecture 3 for leaky enclosures (based on oxygen depletion): • For a heat loss fraction 1= 0.9, Tg,lim = 120 K • For a heat loss fraction 1= 0.6, Tg,lim = 480 K • 1 = 0.6 appropriate for spaces with smooth ceilings & large ceiling area to height ratios • 1 = 0.9 appropriate for spaces with irregular ceiling shapes, small ceiling area to height ratios & where fires are located against walls Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    33. Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    34. Suppression At what rate (litre/min) must water be applied to absorb the heat being released by a fire? • Assume water starts as liquid droplets at 20°C. • Account for the energy required to heat the droplets to 100°C and then vaporize them to steam at 100°C. • Assume density of water is 1000 kg/m3, specific heat in the range 20-100°C is 4.182 x 103 J/(kg °C) and heat of vaporization is 2.26 x 106 J/kg. Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    35. Suppression • Heat absorbed as 1 kg of water heated from 20C  100C  steam is H = 4.182 x 103 J / (kg C) x 80C + 2.26 x 106 J/kg  H = 2.595 x 103 kJ kg-1 • Density of water is 1,000 kg m-3 = 1 kg / litre  H = 2.595 x 103 kJ litre-1 • Define rate of heat release of fire = • Define efficiency of application of water to fire as  < 1 Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    36. Suppression • Divide heat release rate by  times heat absorbed per kg of water that is vaporized to arrive at rate water must be applied in units of kg s-1 • Required rate of application of water (litre s-1) • Assume  = 1/2 and remember 60 s = 1 min • Required rate of application (litre min-1) Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    37. Suppression • For 1,000 kW fire, rate water must be applied is 120 x 1,000 / 2.595 x 103 = 46 litre min-1 • For 6,200 kW fire, rate water must be applied is 120 x 6,200 / 2.595 x 103 = 285 litre min-1 1 US gal = 3.785 litres or 1 litre = 0.264 US gal Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    38. Factors Contributing to Fire Growth (Pre-flashover Fires) • Flammability of room contents: Rate of heat release • Distribution of combustibles (room contents) • Flammability of room linings: propensity for flame spread / rate of heat release • Thermal properties of room linings • Supply of air: size and status of potential openings • Size and shape of room Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    39. Factors Contributing to Fire Severity (Post-flashover Fires) • Flammability: contents & linings: Rate of heat release • Quantity of combustibles • Thermal properties of room linings • Supply of air: size of unprotected openings • Size and shape of room Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    40. Pre-flashover Fires Threats: * life safety in room (& elsewhere) threatened by toxicity, heat & reduced visibility * property in room (& elsewhere) threatened by smoke deposition (corrosivity) & heat * localised structural damage Design Strategies: * inhibit early fire growth * delay or prevent flashover * foster evacuation from room / building Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    41. Pre-flashover Fires Design Options: * limit flammability of contents & linings * limit supply of fresh air * provide early automatic suppression * provide early detection & alarm * limit travel distances & provide adequate exits from room / building Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    42. Post-flashover Fires Threats: * life safety in rest of building threatened by toxicity, heat & reduced visibility * property in rest of building threatened by smoke deposition (corrosivity) & heat * fire spread to other rooms or buildings * structural damage Design Strategies: * delay or prevent fire spread * delay or prevent structural damage * foster evacuation from building * control movement of smoke Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    43. Post-flashover Fires Design Options: * provide compartmentation * ensure adequate spatial separations * ensure structural sufficiency * limit quantity of combustibles * provide automatic suppression * provide adequate means of egress * provide adequate smoke control Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    44. Relative roles of contents and linings in fire dynamics as reflected in fire loss statistics Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    45. Fire Loss Statistics (1) 1982-1996 Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    46. Upholstered Furniture: Fire Loss Statistics 1982-1996 (1) Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    47. Fire Loss Statistics Upholstered Furniture 1982-1996 (1) Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    48. Fire Loss Statistics Upholstered Furniture 1982-1996 (1) Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9

    49. References 1. K.D. Rohr, “Custom Analysis: Examining Fires in Selected Residential Properties”, National Fire Protection Association, Quincy, MA, August 1998. Carleton University, 82.583, Fire Dynamics II, Winter 2003, Lecture # 9