Fire growth index

FIGURE 15.22 THE (fire load) plotted against the PHRR/fig, (fire growth index) for PP-g-MA and the corresponding 5 wt.% LS PP-g-MA nanocomposites (PP-g-MA/LS) at different irradiances 30, 50, and 70kW m-2. 

PA 66-GF is fairly constant, since the polymer is nearly completely combusted for all irradiances used, whereas the THE decreases most for the flame-retarded material at low irradiance, because the char formation is at the highest level. This effect diminishes with increasing irradiance. In the case of Pred in PA 66-GF, combustion is complete at the highest external heat flux, with or without flame retardant, so the THE is almost the same, but the fire growth index is almost halved. Conversely, at low irradiance, not only is the fire growth index reduced, but the THE is almost halved as well. The change in the fire scenario changes the effectiveness of Pred added to PA 66-GF in two of the most important fire properties. Pred in PA 66-GF works best for low external heat flux. Flammability tests like LOI and, much more important, UL 94, are fire scenarios with low external heat flux. 

The fire properties of PE-ZCHS nanocomposites can also be evaluated using fire indices derived from cone data. One fire index is PHRR divided by tig while the fire growth index (FIGRA) is defined as the PHRR divided by tPHRR (70). The values are shown in Table III. Only the 5% loading exhibits improvement on these scales. It is important to note that nanocomposite additives are not effective fire retardants by themselves and should be considered as candidates for formulations that include other additives (13) in order to optimize all fire-related properties. 

The surface burning characteristics (flame spread index and smoke developed index) for wood and wood products as measured by American Society for Testing and Materials (44) can be reduced with fire retardant treatments, either chemical impregnation or coatings (48). Fire retardant treatments also reduce the heat release rate of a burning piece of wood (49,50). The heat release rates (51) of the burning materials are an important factor in fire growth. 

FIGRA index (fire growth rate index) defined as the peak heat release rate in kW during the period from ignition to flashover (excluding the contribution from the ignition source) divided by the time at which the peak occurs (kW/s) ... 

Time to ignition Peak heat release rate Time to peak heat release Total heat release Peak smoke production rate Time to peak smoke production Total smoke production Fire growth rate index (FIGRA)... 

Figure 13.13 Reduction in PHRR, time to ignition (/ign), fire performance indexes (FPI), and fire growth rate (FIGRA) of different PMMA, d ZnAl, and melamine compositions (P=PMMA M=melamine LDH=Zn3Al undecenoate). FPI = /,gn/PHRR and FIGRA = PHRR/time to PHRR. Reproduced with permission from Ref. [85].

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