Flame spread parameter, determination

Determination of the flame spread parameter, (fc. The following well known expression has been given (( ), (6), etc) for the velocity of the flame front for a slab initially at the temperature T = Tg... 

The flame spread parameter experimentally-determined parameter C... 

ASTM E132 was developed as an improvement on the apparatus in ASTM E162 [38]. The specimen size for flame spread studies is 155 by 800 mm by a maximum thickness of 50 mm. This test method determines the critical flux for flame spread, the surface temperature needed for flame spread and the thermal inertia or thermal heating property (product of the thermal conductivity) test. These properties are used mainly for assessment of fire hazard and for input into fire models. A flame spread parameter is also determined, and this can be used as a direct way of comparing the responses of the specimens. It has been used for predictions of full-scale flame performance [39]. 

Equation 3.32 provides an expression for the flame spread velocity based only on the parameters of the problem and on the experimental conditions, but still relies on the presence of an unknown constant that needs to be determined experimentally. 

The main objective of conducting LIFT flame spread experiments is to obtain material properties for predicting opposed-flow flame spread. On the basis of the analysis by deRis (see Equation 14.8), the flame heating parameter can be determined from the slope of a linear fit of l/yjvp(y) plotted as a function of qe (y), where y is the distance from the hot end of the specimen. The minimum surface temperature for spread, Tsmin, is calculated according to an expression akin to Equation 14.4 from the incident heat flux at the maximum distance from the hot end reached by the flame. 

The RCC measures /ign, smoke, CO, specific heat of combustion, mass loss rate, and a variety of other parameters which can help to determine the mechanisms affecting the material flammability. The RCC data is an excellent complement to MFFS data as the MFFS is a measure of the interaction of several of these parameters measured in the RCC. Comparison of the RCC and MFFS data shows the inverse relationship between MFFS and pHRR (Figure 16.17) the higher the pHRR the lower the MFFS. A more detailed explanation of flame spread and more specifically flame spread using the flooring radiation panel apparatus [37] can be found elsewhere [38],... 

An analysis has allowed the authors of Refs. 52 53) to find out a number of interesting features of flame spread over a material surface and investigate the combustion flame structure in the gas and condensed phases. However, the equations obtained contain too many unknown parameters which may be determined only by way of complicated experiments. For this reason the theory in its present form can be used only for rough estimates (e.g. for flame spread limits). 

PaP determined the flammability parameters of 13 materials under different experimental conditions (Table 3.12) for ranking them in terms of a percentage performance as defined for each parameter taking the most favourable value for 100% (where no numerical data can be measured such as in the case of the flame spread rate of rigid PVC, the percentage performance is above 100). The ratings of the 13 materials compared in this way are illustrated in Figures 3.67 to 3.70. 

It has proved difficult to determine any correlation between the test result of the various national procedures [53]. Because of this, the experts of TC92 of the International Standards Organisation (ISO) have undertaken the development of a test procedure to characterise independently ignitability, flame spread, rates of heat release, and other fire-related parameters [54-56]. Worldwide efforts continue to correlate laboratory tests to real-life fires [57]. Examples of such programmes are the corner test programme carried out by Factory Mutual and the corrugated metal tool deck [58] trials [59, 60] carried out by TNO. The corner test has been used to determine the fire behaviour of rigid foam materials when exposed to severe wood crib fire. 

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