Fire Properties of Polymers

The release rates of heat and products from the combustion of solid polymers are expressed as [21, 22]:

Gj = (yj/AHg)(q'e + qf - %) = fj(*}/AHg)(q'l + qf - ^) (11.7)

Qh = (AHch/AHg)(q>: + f - %) = x(AHr/AHg)(% + f - q^) (11.8)

where G j is the mass generation rate of product j per unit surface area of the polymer (g/m2 s), y is the yield of product j (g/g), fj14 is the generation efficiency of product j, ^j is the maximum possible mass stoichiometric yield of product j (g/g), Qc'h is the chemical heat release rate15 per unit surface area of the polymer (kW/m2), AHch is the chemical heat of combustion (kJ/g), AHT is the net heat of complete combustion of the polymer (kJ/g), x is the combustion efficiency, which is the ratio of AHch to AHT. The term yj/AHg is defined as the product generation parameter PGP (g/kJ), and the term AHch/AHg is defined as the heat release parameter (HRP, kJ/kJ) [21, 22].

The release rates of polymer vapors, heat, and products are measured at various external heat flux values in normal air as well in air with variable oxygen concentration and flow rate in the standard test apparatuses [31, 36, 37]. An illustration of the combustion test is shown in Figure 11.6. This test was performed in

13 Combustible polymers, solids, liquids, and gases in general are defined as fuels.

14 fj is the fuel carbon atom conversion efficiency. It is the ratio of the experimental yield of a product j to the maximum possible stoichiometric yield of the product.

15 Chemical heat release rate is the actual heat that is released in the combustion of a polymer [21, 22]. It has a convective and a radiative component. Chemical heat release rate is always less than the heat release rate for complete combustion as the polymers do not burn completely. Chemical heat release rate is determined from the mass generation rate of CO2 corrected for the mass generation rate of CO (defined as the carbon dioxide generation calorimetry) and from the mass depletion rate of O2 (defined as the oxygen consumption calorimetry).

Figure 11.6. Combustion of a liquid fuel soaked in jute cloth wick inside a 100-mm diameter and 25-mm deep Pyrex glass dish in the ASTM E2058 Apparatus. Combustion was performed in normal air at a flow rate of 2.9 x 10-3 m3/s inside a quartz glass tube with no external heat flux.

our laboratory in the ASTM E2058 apparatus in normal air without the external heat flux for a liquid-fuel-soaked wick inside a 100-mm diameter and 25-mm deep Pyrex glass dish.

Examples of the release rates of heat and products measured in the ASTM E2058 Fire Propagation Apparatus and the ASTM E1354 Cone Calorimeter, taken from Refs. [19, 41-44] are listed in Tables 11.9 and 11.10. Table 11.9 lists release rates of products and heat for polymers from parts of a minivan measured in ASTM E2058 Apparatus in normal air and 50 kW/m2 of external heat flux, where data are taken from Ref. [41]. Table 11.10 lists heat release rates measured in ASTM E1354 Cone Calorimeter for various polymers at three external heat flux values, where data are taken from Refs. [42-44]. The HRP (AHch/AHg) values are also listed in Table 11.10, which are obtained from the slopes of the lines representing the relationship between Q)^ and q_l [Eq. (11.8)].

Table 11.9 Peak Release Rates of Heat and Products from the Combustion of Polymers from Parts of a Minivan Measured in the ASTM E2058 Fire Propagation Apparatus3

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G] (g/m2-s)


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