Experimental fires in enclosures

Results are presented of experimental measurements of the mass rates of burning, temperatures, and gas compositions in model enclosures of three sizes. Interest was confined to the fully developed period of burning, in which the burning rate of a combustible-fiberboard crib was limited by the size and shape of the ventilation opening. The burning rate was found to be generally proportional to A(h1/2) (A=area, h=height of window opening), but a characteristic transition region was found for each enclosure, which resulted in a pronounced shift in the data line. Burning-rate data were correlated in terms of the ventilation parameter normalized by the square of the linear-scale ratio. The over-all process involved in enclosure fires appears to be a combined gravity-controlled fluid dynamic regime and a radiation-controlled thermal regime. The dimensionless Froude group is the criterion for similarity in a gravity- (buoyancy-) controlled regime and, from the limited agreement found among the data for the two larger enclosures, this group appears to include the essential parameters in the scaling of burning rates of fires in geometrically similar enclosures.