Influence of excess fuel from timber lined compartments

Abstract External fire spread is a key risk faced by engineers in the design of buildings. This can be quantified by heat flux to an exposed surface, which is dependent on the conditions in the external fire plume. Introducing additional fuel in the form of exposed timber surfaces is shown to increase the energy released by external flaming, as defined by an excess fuel factor or Global Equivalence Ratio (GER). This paper presents a review of three recent experimental series exploring the effects of exposed timber on compartment fire dynamics, and uses experimental data to calculate the GER for each experiment. When combustion efficiency was assumed equal to one, Global Equivalence Ratios were found to range from 0.58 to 3.00; these corresponded to a compartment with a single exposed timber surface and a compartment with three exposed timber surfaces. A “burning factor” has been introduced to as a possible method to relate GER to the properties of the compartment. It is found that a relatively good correlation (R2 > 0.9) is achieved between burning factor and GER when only the compartment surfaces are burning, but that the correlation does not hold when other fuel load is also burning within the compartment.