Abstract
The main aim of the paper is to evaluate the primary factors affecting the safe available evacuation time with the utility of computer modelling, namely Consolidated Model of Fire and Smoke Transport (CFAST) computer model by NIST. The traditionally accepted base value of 2.5 minutes, used in many design standards, may not be appropriate due to its very generalised nature. Hence, a multi-criteria analysis is carried out in which four standard fire scenarios (fire growth rates) are modelled in a set of compartments with varying geometry. The simulation results are assessed against a range of critical conditions, including visibility, toxicity and temperature. Obtained safe available evacuation times are then compared to the standardised values used in design. The results show that the standardised times derived from the 2.5-minutes base value are not as conservative as believed; both under- and overprediction have been identified. The outcomes indicate that a review of the standardised available safe evacuation times should be carried out.
Highlights
Many of fire safety design standards prescribe the maximum allowed length and minimum clear width of escape routes
In fire safety engineering the term Available Safe Evacuation Time (ASET) is used to define this period, there is no direct equivalent in prescriptive fire design codes and various other terms may be used, e.g. Maximum Allowed Evacuation Time (MAET) [1]; for the purposes of this paper the term ASET is used, it does not refer to fire safety engineering design
ASET results from Consolidated Model of Fire and Smoke Transport (CFAST) and Fire Dynamics Simulator (FDS) - 50 m2 area, 2.7 m height compartment
Summary
Many of fire safety design standards prescribe the maximum allowed length and minimum clear width of escape routes. By adhering to these limits, evacuees are assumed not to be exposed to the harmful effects of fire and smoke and to exit the building prior to the onset of untenable conditions. In prescriptive or other traditional codes, ASET is usually not stated directly as a time value but rather as the above mentioned length and width limits. This ASET value is usually based on the 2.5-minutes clearance time indicated in [2]. In light of the age, premise and significant generalisation of the 2.5-minutes value, forming critical part of fire design standards internationally, there is a need for a review of its validity and applicability
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