Fire Dynamics I

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Fire Dynamics I

• Lecture 10
• Burning Rates of Materials Products
• Jim Mehaffey
• 82.575 or CVG7300

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• Burning Rates of Materials and Products
• Outline
• Cone Calorimeter
• heat release rates of materials
• Furniture Calorimeter
• Wooden Cribs
• Wooden Pallets
• Upholstered furniture
• fire loss statistics
• resistance to ignition
• heat release rates
• Design Fires ?t2

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• Cone Calorimeter (3) - ISO 5660 ASTM E1354

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• Cone Calorimeter Data - Thermoset

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• Model for a Thermoset

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• Cone Calorimeter Data - Thermoplastic

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• Model for a Thermoplastic

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• Cone Calorimeter Data - Reduced Oxygen

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• Rate of Heat Release in an Enclosure
• The rate of heat release of an object burning in
  an enclosure may differ from its free burning
  rate as a consequence of a competition between
  two effects
• Radiant heat transfer from the hot upper layer or
  ceiling flames increases the rate of burning.
• Reduced air (oxygen) flow to the burning item
  reduces the rate of burning.

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• Furniture Calorimeter
• The rate of heat release of a product burning in
  the open can be measured using a furniture
  calorimeter.
• ASTM E1537 Standard test method for fire testing
  of real-scale upholstered furniture items
• ASTM E1590 Standard test method for fire testing
  of real-scale mattresses
• ASTM E1537 and 1590 specify a propane burner
  which simulates a newspaper fire. Other ignition
  sources can, however, be used with the apparatus.

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• Furniture Calorimeter

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• Wooden Pallets (1)

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• Wooden Pallets

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• Wooden Pallets - Peak Burning (in the open)
• Eqn (10-1)

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• Wooden Pallets - Theory vs. Experiment

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• Wooden Pallets
• For non-standard pallet sizes,
• Eqn (10-2)
• Heat release rate per unit floor area covered by
  pallet stack

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• Wooden Pallets - Mass Loss Rate
• The heat release rate mass loss rate are
  related by
• Eqn (10-3)
• Implicitly assumed that Hch 12 kJ g-1
• Knowing can calculate, radiative and
  convective components of heat release rate, and
  rates of generation of CO and soot.

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• Wooden Pallets in an Enclosure
• Radiation from upper layer has little impact on
  because fire is largely self-contained with
  many surfaces seeing each other.
• If fire is limited by ventilation, will be
  reduced.

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• Wooden Cribs (1)

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• Wooden Cribs
• D stick thickness (m)
• S spacing between sticks (m)
• hc height of crib (m)
• N number of rows hc / D
• n number of sticks per row
• L length of each stick (m) L gtgt D
• ? density of sticks (kg m-3)
• mo initial mass of crib (kg) N n ? D2 L

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• Steady-State Burning of Wooden Cribs
• Fuel surface controlled burning Stick surfaces
  burn freely S gtgt D
• Eqn (10-4)
• mass loss rate of crib (kg s-1)
• to time at which steady burning is established
  (s)
• vp surface regression rate (m s-1)

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• Steady-State Burning of Wooden Cribs
• Crib porosity controlled burning Burning
  controlled by rate of flow of air combustion
  products through holes in crib S ltlt D
• Eqn (10-5)
• for t gt to is given by lesser of Eqns
  (10-4) (10-5)

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• Growth Rates - Burning of Wooden Cribs
• Assume crib is ignited at bottom / centre
• to time at which steady burning is established
  (s)
• For t lt to
• Eqn (10-6)
• to time Eqn (10-6) yields lesser of Eqns (10-4)
  (10-5)
• 
  
• For a crib ignited at bottom / centre and whose
  steady-state burning is fuel-surface controlled
  to 15.7 n (s)

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• Wooden Cribs - Heat Release Rate
• The heat release rate is given by
• Eqn (10-3)
• with Hch 12 kJ g-1
• Knowing one can also calculate, radiative
  and convective components of heat release rate,
  and rates of generation of CO and soot.

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• Wooden Cribs in an Enclosure
• Radiation from upper layer has little impact on
  because fire is largely self-contained with
  many surfaces seeing each other.
• If fire is limited by ventilation, will be
  reduced.

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• Upholstered Furniture Fire Loss Statistics
• 1982-1996 (2)

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• Upholstered Furniture Fire Loss Statistics
• 1982-1996 (2)

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• Upholstered Furniture Fire Loss Statistics
• 1982-1996 (2)

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• Upholstered Furniture Fire Loss Statistics
• 1982-1996 (2)

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• Resistance to Ignition - USA
• Upholstered Furniture Action Council (UFAC)
• In 1979, UFAC introduced a voluntary program
  intended to make upholstered furniture more
  resistant to cigarettes
• 24 x 106 pieces of furniture sold annually in US
  join 350 x 106 pieces in use. Estimated life is
  30 years.
• By 1988, 91 of volume of new upholstered
  furniture was UFAC approved
• From 1978-1986, 55 reduction in number of fires
  starting on upholstered furniture. Could be due
  to
• better furniture
• fewer smokers
• earlier detection (smoke detectors)

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• Resistance to Ignition - UK
• Upholstered Furniture (Safety) Regulations 1980
• Upholstered furniture must resist ignition by
  cigarettes and matches
• Resistance to Ignition - Canada
• Hazards Product Act. Mattress must exhibit
  resistance to ignition by cigarettes
• Upholstered furniture Program similar to UFAC
  introduced in early 1980s

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• Upholstered Furniture
• European Statistics (3)
• Fires starting in upholstered fires
• Cause 49 of deaths in dwellings
• Cause 15 of deaths in public buildings
• 42 ignition by smokers materials

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• Upholstered Furniture Mattresses
• European Experiments (3)
• Tested numerous pieces of commercially available
  upholstered furniture (sofas and chairs) and
  mattresses
• Test conducted in a furniture calorimeter
  employing Nordic Standard NT Fire 032
• Used flaming (not smouldering) ignition source
• Identified four basic levels of performance

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• Upholstered Furniture Mattresses
• European Experiment Data (3)
• Heat release rate (HRR) as function of time for
  representative selection of European upholstered
  furniture mattresses

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• Upholstered Furniture Mattresses
• European Regulations?
• Fire safety acceptance criteria have been
  proposed to the European Commission

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• Design Fires ?t2
• Characterize growth phase of fire by
• ? (t - tig)2 Eqn (10-7)
• heat release rate (kW)
• ? growth coefficient (kW s-2)
• tig time to flaming ignition (s)

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• Design Fires ?t2 - Examples
• Eqn (10- 6) for growth rate of crib fires
• Page 10-13 for growth rate of wooden pallets with
  tig 100 s and ? 0.047 kW s-2
• 
  
  
  
  
  
• Burning sofa
• cushions filled
• with foam plastic

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• Design Fires ?t2

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• References
• 1. V. Babrauskas, Burning Rates, Section 3 /
  Chapter 1, SFPE Handbook, 2nd Ed. (1995)
• 2. K.D. Rohr, Custom Analysis Examining Fires
  in Selected Residential Properties, National
  Fire Protection Association, Quincy, MA, August
  1998.
• 3. B. Sundström, S.J. Grayson and P. Van Hees,
  Short Communication An Overview of the Findings
  of the Combustion Behaviour of Upholstered
  Furniture Project, Fire and Materials 20,
  205-211 (1996)