Experimental study on the characteristics of horizontal flame spread over XPS surface on plateau.
A series of comparative laboratory-scale experiments were carried out in the Lhasa plateau and the Hefei plain respectively to investigate the characteristics of flame spread over the extruded polystyrene (XPS) foam, a typical thermal insulation material. Flame shape and the temperature profile in solid phase were monitored, and the effects of altitude on the heat transfer process were analyzed. The results show that the temperature rise with time undergoes three stages: the preheating stage, the melting stage and the pyrolysis stage. The durations of the melting and pyrolysis stages on plateau are longer than that in plain, which sequentially results in a lower flame spread rate on plateau. Comparing of the temperature change rate curve on plateau with that in plain, it is found that the peak characteristics of the curves in the pyrolysis stage changed from single peak to multi-peaks, which suggests that the altitude difference might change the pyrolysis mechanisms of XPS material. Moreover, the sample scale effects on flame spread are also explored. Two different regimes are found in flame spread behavior with sample scale at the both altitudes. The spread rate drops with sample scale in convection regime and rises in radiation regime.
Plastic pool fires
Abstract Experimental results relating flame radiation feedback mechanisms to the burning behavior of 51 mm-thick, solid, horizontal, square, polymethyl methacrylate (PMMA) pools are discussed. Data for sizes ranging from 25 mm × 25 mm to 1.22 m × 1.22 m show that the burning rate per unit surface area of plastic pool fires increases with scale and is dominated, at the larger scales, by thermal radiation from the flames. The total radiative power output of the flames represents 42% of total heat release rate of the larger PMMA fires. Local burning rates for the larger plastic pools are maximum at pool center, corresponding to maximum radiative heat transfer from the flames, and decrease monotonically to the edge of the pool. Relatively long time periods are required to establish steady burning in the intermediate sized pools. The long “burn-in” time to reach steady state is associated with increasing radiative heat flux from the flames to the pool with time. The magnitude of the time-dependent radiative heat flux to the pool is calculated on the basis of a one-dimensional analysis for a semi-infinite slab. The variation of local burning rates along the pool surface is formulated in terms of a cylindrical flame model. Physical implications of the assumptions made in the analysis and their limitations are reviewed critically.
Experiments on the burning of cross piles of wood
Experiments have been performed in which geometrically scaled, unenclosed, cross piles of wood were burned under controlled conditions. For sticks of square cross section ranging in size from 0.16 to 9.15 centimeters, t he typical weight-time curve illustrated the t hree characteristic stages: ignition, active combustion, and decay. For the active combustion stage, the maximum rate of burning (rate of weight loss) was determined and all the test data were correlated in ter ms of a porosity factor involving t h e vent area of the pile and the exposed surface area of t he sticks. The correlation between the scaled r ate of burning and t he porosity factor may be simply considered in terms of three regions: a. Diffusion-limited co mbustion, in which t he sc&led rate of burning is very nearly propor tional to t he porosity factor, b. free combustion, in which the scaled rate of burning is independent of the porosity factor, and c. lJonsustained combustion, in which t he openness of the pile prevents the maintenance of combustion. Similari ty considerations of flame height and radiant intensity data indicate t hat a simple model may adeq uately describe the natural convection burning of cross piles of wood of t he type and size range investigated.