Experimental and theoretical analysis of quasi-steady small-scale enclosure fires

Abstract

Forty-six small-scale experiments were conducted to measure the characteristics of horizontal plastic (PMMA) pool fires in an enclosure as a function of doorway width and fuel area. A 0.30 m high enclosure was instrumented to measure sample mass loss, the upper gas layer and ceiling temperatures, heat flux to the floor, and the pressure drop across the doorway. Results are reported for the maximum steady burning period; however, a few cases do not seem to have reached a steady state. For small sample sizes, a distinct fire plume could be perceived in the enclosure, while for larger sample sizes flames tended to fill the enclosure (sometimes to within 2 or 3 cm of the floor), and extended out the door opening. The rate of mass loss is a strong function of the radiative feedback from the enclosure. However, reduced oxygen concentration in the flow entrained by the fire plume seems to affect the mass loss rate. For the smaller doorway widths, the rate of mass loss increases almost directly with ventilation. As the width is increased, the mass loss rate instead becomes a function of sample area and radiative heat transfer. For some sample sizes, as the doorway width is increased a maximum rate of mass loss is achieved, followed by a decrease in burning rate at higher ventilation levels. The temperatures and floor heat flux also tend to follow this trend. The data were then compared to the results of a theoretical model. Agreement between theory and data is qualitatively good. But overall, good quantitative agreement is not achieved. This lack of agreement appears consistent with inaccuracies of the flame radiation model and an incomplete description of the flame chemistry.