Determination of Separation Distances Inside Large Buildings

In this study, an analytical framework is developed to determine the hazards posed by an uncontrolled fire burning indoors. This scenario, unlike unconfined outdoor fires, has received little attention in the literature and associated engineering methods for risk evaluation are unavailable. The present analyses are limited to overventilated fires burning in large non-combustible buildings. Hazards are evaluated on the basis of thermal radiation and firebrand transport. Thermal radiation is assessed using a solid flame radiation model; transport of firebrands is evaluated taking into consideration the convective ceiling layer established by the fire plume. Given the considerably different geometry of the scenario of interest herein, as compared to unconfined fires, efforts are placed in developing a rigorous physical and mathematical approach so as to make the developed methodology sufficiently general. The model derived is validated against limited heat flux data obtained for free-burn fires (up to 50 MW) involving Class 2 commodity rack storage arrays. In addition, general trends are investigated using a hypothetical sample scenario. Results show that thermal radiation is the main phenomenon driving the hazards encountered in indoor fires; firebrand transport, due to ceiling confinement, presents a much lesser hazard.