Improved Fire- and Smoke-Resistant Materials for Commercial Aircraft Interiors A Proceedings (1995) / Chapter Skim
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Chapter 6. Fire Properties of Materials
Chapter 6. Fire Properties of Materials
Pages 61-92
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From page 61... ...
The relationships between the firehardening of materials and fire properties are enumerated. Fire-hardening is defined as a process where resistance to pyrolysis, ignition, combustion, and fire propagation is increased, and release rates of heat and fire products are decreased.
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From page 62... ...
Radiative heat of combustion (AH,~ Yield of a product Energy required to pyrolyze a unit mass of a material origimally at ambient temperature Heat lost to the environment from the hot surface Amount of a product generated per unit mass of a material pyrolyzed Amount of a product generated in pyrolysis per unit; amount of energy required to pyrolyze a unit mass of a material Ignition Process Minimum heat flux at or below which a flammable vapor-air mixture is not created Ease of in-depth penetration of the thermal wave and time delay to reach the ignition temperature Combustion Process Heat flux transferred from the flame back to the surface Amount of energy released in the complete combustion of a unit mass of a material pyrolyzed with water as gas Amount of energy actually released in a fire from the combustion of a unit mass of a material pyrolyzed Component of the chemical heat of combustion carried away from the flame by flowing combustion product-air mixture Component of the chemical heat of combustion transmitted away from the flame by radiation Amount of a product generated in the combustion per unit mass of a material pyrolyzed
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From page 63... ...
Corrosion damage by products· · . corrosion index Amount of energy generated in combustion per unit amount of energy required to pyrolyze a unit mass of a material Amount of a product generated in combustion per unit; amount of energy required to pyrolyze a unit mass of a material Fire Propagation Extent and rate of fire propagation beyond the ignition zone Nonthermal Damage Maximum distance over which an observer can see Smoke damage due to discoloration, smell, or electrical malfunction Toxic effects of products on humans Rate of corrosion per unit mass concentration of a material pyrolyzed PYROLYSIS When a material is exposed to heat flux, pyrolysis products are generated.
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From page 64... ...
Results from numerous small- and large-scale fires show that, as the surface area of the burning material increases, the flame radiative heat flux increases and reaches an asymptotic limit, whereas the flame convective heat flux decreases and becomes much smaller than the flame radiative heat flux at the asymptotic limit (Hottel, 19591. In small-scale experiments with fixed surface area, flame radiative heat flux increases and flame convective heat flux decreases with increase in the oxygen mass fraction (Ye)
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From page 65... ...
Modifications in the pyrolysis behavior to enhance release of higher monomer fraction relative to oligomer fraction and reduction in the carbon atom fraction relative to other atoms in the pyrolysis products (enhanced surface charring) would reduce the flame heat flux transferred back to the surface and the mass pyrolysis rate (Equation 3~.
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From page 66... ...
66 In 0~8 i, o' i- O ° i-O 3 ~ 1 NOI103S d~ddn WtO'Z Ct A: 111 z o J ~ Z o <: Ct ~ o J ~ m<: Improved Fire- aru] Smoke-Resistant Materials · ~ / ~~ \ z ~ ~ g O2 'JJ ~ Z O ~ ~ ~ ~ O ~ ~ A LLI A ilk' < O Q a)
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From page 67... ...
The mass pyrolysis rate is directly proportional to the heat release rate and the generation rates of products. Decrease in the mass pyrolysis rate, thus, would reduce the thermal and nonthermal hazards.
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From page 68... ...
7 - 52 (Teflon) Aflame Radiation Scaling Technique: Pool diameter fixed at 0.10 m, Yo20.30.
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From page 69... ...
. For thermally thick materials, the square root of time to ignition is directly proportional to TRP and inversely proportional to the external heat flux.
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From page 70... ...
Thermal Response Parameter (TRP) The TRP values depend on the physical and chemical characteristics of the materials.
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From page 71... ...
, assumed to be constant; Of is the flame heat flux transferred ahead of the pyrolysis front (kW/m21; and ~T,,:~kpcp is the TRP for the thermally thick materials in kW · s''2/m2 (Equation 41. The flame heat flux transferred ahead of the pyrolysis front is a function of the rate of heat actually released in the fire-propagation process, defined as the chemical heat release rate.
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From page 72... ...
< l ~ 0.233 400 600 800 1 000 1 200 1 400 Time (s) FIGURE 5 Chemical heat release rate versus time for the downward fire propagation, steady combustion, and flame extinction for 300-mm long, 100-mm wide, and 25-mm-thick PMMA vertical slab under opposed air flow condition in the FMRC Flammability Apparatus.
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From page 73... ...
Numerous correlations have been developed for the relationship between the flame heat flux transferred ahead of the pyrolysis front and the radiative heat-release rate, one of which is ~ewarson and Khan, 19881: Off a' tirade 2/3 (7) where Q',~ is the radiative heat release rate per unit width or circumference of a slab or a cylinder of a material respectively (kW/m)
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From page 74... ...
Fire propagation beyond the ignition zone is limited. 10 < FPI < 20: Fire propagates slowly beyond the ignition zone.
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From page 75... ...
An increase in the TRP value and a decrease in the chemical heat release rate by the various techniques discussed in the previous sections would lead to FPI values that are ~ 7. GENERATION OF HEAT AND FIRE PRODUCTS As a material is exposed to heat in the ignition zone, the first step is the generation of the pyrolysis products.
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From page 76... ...
By' ~ I' - if' (13) The ratio of the chemical heat of combustion to heat of gasification, AHC,,/AH:, is defined as the heat release parameter CARP)
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From page 77... ...
By knowing or predicting the net heat flux for a fire scenario, the chemical heat release rate can be calculated from Equation 13. 1 .2 1.04 8 0.8 I `, 0.6 ~L I 0.4 0.2 o.o I I I I i I I'I I I 10-1 10° 1 1 ~_b ~ ___ _ orb q it's + Wood · PMMA Nylon O PE PP O PS 1 01 Equivalence Ratio 1o2 FIGURE 6 Ratio of the heat release parameter for the ventilation-controlled to well-ventilated combustion of materials versus the equivalence ratio.
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From page 78... ...
The stoichiometric yields of the products provide an insight into the nature of the products and the maximum possible mass generation rates of products expected in pyrolysis and combustion processes in fires. The ratio Y.11tj is defined as the generation efficiency of the product j, A
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From page 79... ...
Techniques to reduce the HRP values, discussed previously, would also help to reduce the PGP values. The CO and smoke PGP values for selected materials are listed in Table 7, along with the FPI values and the group classification.
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From page 80... ...
The values of c' and ~ are strongly dependent; whereas, the value of `S is weakly dependent on the chemical structures of the nonhalogenated materials. The ventilation correlation coefficient c' primarily reflects the magnitude of the fire properties in nonflaming fires (high ~ values)
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From page 81... ...
I 2 ~ ~ ////.//. /~/ Nonfloming ~ · PUMA , Nylon , PE iO PP ~ 10° Equivalence Ratio 10' FIGURE 8 Ratio of the smoke generation parameter for ventilation-controlled to well-ventilated combustion of materials versus the equivalence ratio.
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From page 82... ...
This paper deals with the subject of nonthermal damage in industrial and commercial occupancies due to smoke and corrosive fire products. The subject of corrosion for commercial and industrial occupancies has been reviewed based on the knowledge denved from the telephone central office (TCO)
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From page 83... ...
and on laboratorvscale pyrolysis and combustion experiments. _ _ , _ _ _ _ , In fires mew surfaces are exposed to fire products that include water (generated in the combustion process and present in the ambient airs.
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From page 84... ...
and WT is the total mass of the material pyrolyzed (kg)
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From page 85... ...
It has been suggested that soot nucleation and growth occur near the highly ionized regions of the flames in combustion processes and that some of the charges are transferred to smoke particles. Smoke damage in industrial and commercial occupancies is considered in terms of discoloration and odor of the property exposed to smoke; interference in the electric conduction path and corrosion of the parts exposed to smoke is a carrier of the corrosive products.
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From page 86... ...
the heat of combustion need to be decreased to reduce the mass pyrolysis rate in the combustion and the heat release rate. These two fire properties could be reduced by (~)
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From page 87... ...
FIGURE 11 Ratio of the HRP in the presence and absence of Halon0 1301 for the well-ventilated combustion of polyester-70 percent glass composite system exposed to 60 kW/m2 of external heat flux. Data are from the FMRC Flammability Apparatus.
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From page 88... ...
rule neat release rate wlthm each ilrepropagation group is characterized by the heat release parameter (HRP) (or the ratio of the heat of combustion to heat of gasification)
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From page 89... ...
(kW/m2) heat release rate per unit sample width (kW/m)
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From page 90... ...
1977. The dependence of flame propagation on surface heat transfer.
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From page 91... ...
1994. Flammability parameters of materials: Ignition, combustion, and fire propagation.
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