Duct Fires

Abstract

This report analyzes fuel rich fires spreading within ventilated fuel-lined ducts. The conditions for the occurrence of these intense high hazard fires are discussed. Overall energy balance arguments can be used to predict the fire spread velocity provided one knows: (1) the energy H _vap required to vaporize unit mass of fuel at ambient temperatures and (2) the net heat loss rate Q _L to the side walls. The present lack of information on H _vap for wood is discussed and some experimental measurement techniques are proposed. In addition a detailed mathematical model for fuel rich duct fires: (1) verifies the overall energy balance relationship, (2) accounts for the various energy flows including the heat loss Q _L, and (3) provides a calculation of the temperature distributions in the gas and walls. These calculations are in agreement with the extensive experiments performed by Roberts el al. (1966, 1967a, 1967b). The conceptual understanding provided by this analysis of fuel-rich fires should prove helpful in interpreting the results from standard duct-like material flammability tests.