Fire Dynamics II

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Fire Dynamics II

• Lecture 9
• Room-fire Dynamics
• Jim Mehaffey
• 82.583

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• 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

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• Introduction

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• Upper Layer Temperature During an Enclosure Fire

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• 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

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• 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

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• 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 500-600C
• 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

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• 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

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• Impact of boundary (thermal properties)

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• 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)

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• Impact of size of openings

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• 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)

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• 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

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• 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 ?

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• 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

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• 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

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• 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

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• Temperature Profile in Living Room

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• Temperature Profile in Bedroom

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• Room Fire Test - Apparatus
• ISO 9705 Fire tests Full scale room fire tests
  for surface products
• Contribution of room linings to fire growth
  (flashover)

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• 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

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• Room Fire Test - Results

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• 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

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• CAN/ULC-S102 Gypsum Board
• At (gypsum board) A1 A2 8.0 m min
• ? FSR (gypsum board) 15

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• CAN/ULC- S102 Polyurethane Foam Insulation
• FSR (PU foam insulation) 427 (d/t) or 74 (At)

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• Room Fire Test - Video
• Test follows ISO 9705
• Walls ceiling wooden panelling
• Time to flashover ? 300 min

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• 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?

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• Simulation of Rhode Island Fire - Video
• Demonstrates rapid ignition and flame spread over
  exposed foamed plastic insulation

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• 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

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• 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

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• 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 20C.
• Account for the energy required to heat the
  droplets to 100C and then vaporize them to steam
  at 100C.
• Assume density of water is 1000 kg/m3, specific
  heat in the range 20-100C is 4.182 x 103 J/(kg
  C) and heat of vaporization is 2.26 x 106 J/kg.

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• 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 ? lt 1

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• 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)

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• Relative roles of contents and linings
• in fire dynamics as reflected in
• fire loss statistics

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• Fire Loss Statistics (1)
• 1982-1996

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• Upholstered Furniture Fire Loss Statistics
• 1982-1996 (1)

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• Fire Loss Statistics
• Upholstered Furniture
• 1982-1996 (1)

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• Fire Loss Statistics
• Upholstered Furniture
• 1982-1996 (1)

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• References
• 1. K.D. Rohr, Custom Analysis Examining Fires
  in Selected Residential Properties, National
  Fire Protection Association, Quincy, MA, August
  1998.