Fire Dynamics I

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Fire Dynamics I

• Lecture 11
• Flammability of Solids
• Jim Mehaffey
• 82.575 or CVG7300

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• Flammability of Solids
• Outline
• Characterizing flammability
• Non-combustibility test
• Degrees of combustibility test
• Room fire test
• Flame-spread ratings
• Corner wall test
• Flame spread models

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• Characterizing Flammability Common Descriptors
• 1. Ignitability (piloted // non-piloted)
• ignition temperature
• critical flux for ignition
• time to ignition (scenario dependent)
• 2. Combustibility
• noncombustible vs combustible (temperature rise
  / persistence of flaming / mass loss)
• degree of combustibility (heat release)
• 3. Heat release
• rate of heat release vs time
• peak rate of heat release
• total heat released

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• Characterizing Flammability Common Descriptors
• 4. Flame spread
• arbitrary index
• rate of flame spread
• extent of flame spread
• critical flux for flame spread
• 5. Production of smoke and toxic gases
• rate, peak and total
• Which descriptors best assess a solids
  flammability depends on the scenario of interest
  and hazard of concern. When countries developed
  test methods to regulate wall coverings, they
  devised different tests that measured different
  aspects of flammability.

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• European Flammability Tests
• Project conducted by H.W. Emmons, Harvard Univ.
• 24 wall coverings were tested in 6 countries.
  Each country used its own test method.
• In each country, coverings were ranked 1, 2,
  23, 24 according to their performance. 1
  exhibited the worst performance 24 exhibited the
  best.
• An average ranking for each covering was
  established by averaging its rank in all 6 tests.
• A graph was constructed with the ranking for each
  covering in each country on the ordinate and the
  average for each covering on the abscissa

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• European Flammability Tests
• Order of flammability of 24 wall coverings as
  tested in 6 countries. If each test measured the
  same property, all point would fall along the
  diagonal.

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• European Flammability Tests
• Order of 24 materials drawn 6 times from deck
  of cards. Plot reflects random process. Same as
  flammability study.
• Europe is now harmonizing its test methodology

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• Combustible vs Noncombustible Building Materials
• Ignitability measure of ease of ignition
• surface temperature at ignition
• critical heat flux
• time to ignition for flux gt critical heat flux
• Combustibility measure of potential to
  contribute to fire
• In Canada, a building material is noncombustible
  if it meets the acceptance criteria of
• CAN4-S114, Standard method of test for
  determination of non-combustibility in building
  materials
• Otherwise it is combustible

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• CAN4-S114 Test Apparatus

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• CAN4-S114 Test Apparatus
• Test specimen 38 x 38 x 50 (mm)
• Condition specimens for 24 to 48 h at 60 ? 3C
  and let cool to room temperature
• Stabilize furnace at 750 ? 3C for 15 minutes
• Specimen inserted and monitored for 15 minutes
  (or until it fails)

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• CAN4-S114 Acceptance Criteria
• Building material is non-combustible if
• Average maximum temperature rise (3 tests) ? 36
  C
• No flaming during last 14 min 30 s in any of 3
  tests
• Maximum mass loss ? 20 in any of 3 tests
• A pass / fail test
• No measure of degree of combustibility

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• CAN4-S114 Observations
• Furnace is at temperature 750 C 1023 K
• Emissive power of internal walls of furnace is
• E1 ? ? T4 0.9 x 5.67 x 10-8 W m-2 K-4 x
  (1023 K)4
• E1 56 kW m-2
• Heat flux at surface of specimen is
• E1 F1-d2
• The configuration factor would be high ( 1) so
  flux exceeds critical radiant flux for
  auto-ignition of wood namely 28 kW m-2

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• CAN4-S114 Observations
• Mass loss ? 20 excepts hydrated materials that
  are not combustible
• Gypsum is CaSO4 2H2O so is about 21 by mass
  chemically bound water
• The chemically bound water is driven from gypsum
  between 100 to 200C.
• Core of gypsum board is about 70 gypsum
• Core of gypsum board losses about 15 of its mass
  in test so classified as noncombustible

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• CAN4-S114 Douglas Fir
• Douglas fir is classified as combustible

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• CAN4-S114 Glass-fibre Insulation
• This glass-fibre insulation is classified as
  combustible

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• CAN4-S114 Aluminium
• Aluminium is classified as non-combustible

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• Combustible vs. Non-combustible
• Combustible materials wood products, paper,
  plastics, felt (animal or vegetable fibres)
• Non-combustible materials brick, ceramics,
  metals, glass, granite, sandstone, slate, marble,
  plaster (gypsum non-combustible
  aggregate), concrete (portland cement non-comb
  aggregate)
• Analogous US test is ASTM E136. Temp rise
  criterion is assessed at specimen centre. ASTM
  E136 ? to be non-combustible must have less than
  3-4 organic content.
• Addition of fire retardants does not usually make
  a material non-combustible.

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• National Building Code Requirements
• Non-combustible construction
• Structural members non-combustible
• Restricted use of combustibles elsewhere (3.1.5.)
• Combustible construction
• Wood-frame or heavy timber
• Whether bldg must be of non-combustible
  construction or is permitted to be of combustible
  construction depends on
• major occupancy
• number of storeys
• building area
• number of streets building faces
• presence of sprinklers

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• Shortcomings of Non-combustibility Test
• A severe pass / fail test
• No measure of degree of combustibility (that is
  actual performance)
• Treats materials not products like gypsum board

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• Degrees of Combustibility Test
• CAN/ULC-S135, Standard method of test for
  determination of degrees of combustibility of
  building materials using an oxygen consumption
  calorimeter (cone calorimeter)
• Specimen subjected in cone calorimeter to heat
  flux of 50 kW m-2 in presence of spark ignition
  source for 15 minutes
• Observations and potential means for
  classification
• time to ignition (s)
• heat release rate (peak) (kW m-2 )
• total heat released (kJ m-2 )

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• Factors Affecting Rate of Spread of Flame
• Material Factors
• Chemical Composition of fuel
• Presence of fire retardants
• Physical Initial temperature
• Surface orientation
• Direction of propagation
• Thickness
• Thermal conductivity
• Specific heat
• Density
• Geometry
• Continuity

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• Factors Affecting Rate of Spread of Flame
• Environmental Factors
• Composition of atmosphere
• Temperature
• Imposed heat flux
• Air velocity

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• Spread of Flame over Wall Linings

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• Spread of Flame over Wall Linings

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• Room Fire Test - Apparatus
• ISO 9705 Fire tests Full scale room fire tests
  for surface products

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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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• Flame-spread Ratings - Building Materials
• CAN/ULC-S102 "Standard Method of Test for
  Surface-Burning Characteristics of Building
  Materials and Assemblies
• CAN/ULC-S102.2 "Standard Method of Test for
  Surface-Burning Characteristics of Flooring,
  Floor Coverings, and Miscellaneous Materials and
  Assemblies"

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• Flame-spread Ratings - Test Apparatus

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• Flame-spread Ratings - Test Apparatus
• Test equipment Horizontal tunnel
• 7.6 m long 450 mm wide 300 mm deep
• Roof Removable
• Low-density mineral board
• Walls and Floor Fire brick
• Observation windows Along one wall

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• Flame-spread Ratings - Test Method
• Condition specimen at 23 ? 3C and relative
  humidity of 50 ? 5
• Natural gas flames (2 burners) forced down tunnel
  by draught 1.2 m s-1
• Burners f lames 1.37 m long // ? 90 kW
• Flames impinge on specimen mounted on ceiling
  (S102) or floor (S102.2)

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• Flame-spread Ratings - Test Method
• Calibration Adjust so it takes 5.5 min for
  flames to travel to end of red oak specimen
• In exhaust duct Light source detector to
  measure obscuration due to smoke
• Test protocol Monitor advance of flame smoke
  obscuration for 10 min
• Run 3 tests for each product

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• Flame-spread Rating (FSR)
• Fixed points
• Red oak . . . . . . . . . . 100
• Inorganic board . . . . . . 0
• Determination of rating
• Plot flame front position vs time
• Calculate area At under curve ignoring recessions
• FSR 1.85 At if At ? 29.7 m min
• FSR 1640 / (59.4 - At) if At gt 29.7 m min

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• Flame-spread Rating (FSR)
• If initial rapid advance
• FSR 92.3 d / t
• d distance of rapid advance (m)
• t time of rapid advance (min)
• or employ
• ULC-S127, Standard corner wall method of test
  for flammability of non-melting building
  products

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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 Loose-fill Cellulose Insulation
• At (loose-fill cellulose insulation) A1 A2
  30 m min
• ? FSR (loose-fill cellulose insulation) 55

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

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• Comparison with ASTM E84
• ASTM E84 specimen tested in ceiling // only
  uses area expressions (with different
  coefficients)
• When area expressions governs (S102)
• FSR (E84) ? 0.92 FSR (S102)
• When rate expression governs (S102)
• FSR (E84) lt FSR (S102)
• When products tested to S102.2, generally
  difficult to compare. However for melting
  materials
• FSR (E84) lt FSR (S102)

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• Comparison with Room Fire Tests
• NBCC requires protective barrier for foam
  plastic insulation

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• Corner Wall Test
• ULC-S127, Standard corner wall method of test
  for flammability characteristics of non-melting
  building materials

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• Corner Wall Test
• Test chamber cubical - 1300 mm
• Test specimen 2 walls, ceiling canopies
• Ignition source 33 kW natural gas burner
• Measure time (s) until thread breaks

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• Corner Wall Test

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• Building Code Requirements Interior Finish
• Purpose If interior finish ignited early in
  fire, flames must not spread so quickly that
  occupants are unable to escape
• Example An apartment building (no sprinklers)

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• Shortcomings with the Tunnel Test
• FSR is not a fundamental property. It cannot be
  used to predict rate of flame spread in filed
  conditions that differ from test conditions.
• For example performance in tunnel is unrelated
  to
• performance of foamed plastic insulation in a
  wall cavity
• performance of textile coverings on walls
• performance of interior finish exposed to
  external radiant flux

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• Flame Spread Models Concepts
• Flame spread an advancing ignition front
• Leading edge of flame is heat source (raising
  fuel to ignition temp) and the pilot
• Visually flame spread ? advancing flame close to
  solid
• Two interacting advancing fronts
• flame front in gas phase
• pyrolysis front along solid surface
• Heat transfer from flame ? pyrolysis front to
  advance
• Advance of pyrolysis front ? increased release of
  volatiles ? advance of flame front
• Flame-spread velocity ? rate of advance of
  pyrolysis front

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• Wind-aided Spread

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• Wind-aided Spread
• ? region of heat transfer from flame smoke
• For wind-aided spread 0.1 m ? ? ? 10 m
• For opposed-flow spread 1 mm ? ? ? 3 mm
• Surface temperature in control volume drops from
  Tig to Ts
• Pyrolysis front moves at speed
• Model for wind-aided flame spread

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• Example of Acceleratory Flame Spread
• Upward turbulent spread on thick PMMA
• xb 0 and n 0.94 1
• Experiment finding
• When xp 1.0 m, v 5.0 mm s-1

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• Example of Constant Flame Spread
• Upward turbulent spread on thin textiles
• n 0.6
• After some time, (xp - xb) and v become constant

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• Opposed Flow Spread Model for Thick Materials
• Quintiere and Harkleroad, 1985
• ? flame-heating parameter (kW2 m-3) material
  property
• Provided no dripping, this model holds for
• downward flame spread (wall)
• lateral flame spread (wall)
• horizontal flame spread (floor)
• ?, k?c and Tig - measured (LIFT apparatus)
• Ts - depends on scenario (external flux)

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• LIFT Apparatus - Standard Tests
• ASTM E1321, Standard test method for determining
  material ignition and flame spread properties
• ISO 5668, Fire tests Reaction to fire surface
  spread of flame on building products

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• LIFT Apparatus

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• LIFT Apparatus - Results