Five fire scenarios have been simulated with the CFD model Fire Dynamics Simulator (FDS) to analyse the performance-based fire safety design of a 2935 m-long railway tunnel. The influence of tunnel longitudinal ventilation fan activation time, fire size and the type of burning materials on tunnel tenability was investigated based on variations of two primary scenarios: Scenario #1 assumed a 15 MW fire at the front end of a train, and Scenario #2 assumed a 15 MW fire at the rear of a train. In both scenarios the burning material was assumed to be predominantly polyurethane, and tunnel fans were assumed to activate 901 seconds after fire initiation. Scenario #3 was a variation of Scenario #1 with the dominant burning material changed to wood; Scenario #4 was a variation of Scenario #2 which assumed that fans activated 180 seconds after fire initiation; and Scenario #5 was a 6 MW fire, which was scaled down from the 15 MW fire of Scenario #1.For all of the scenarios, a reversible bi-directional ventilation strategy was implemented, and the worst wind condition was considered. The burning materials (polyurethane and wood) were assumed to generate a soot rate of 10% and 1% per unit weight of fuel respectively. Maximum tenable time (known as Available Safe Egress Time, ASET hereafter) was computed based on a visibility limit of 10 m at a height of 2.1 m.CFD virtual realisation results showed that the fire heat release rate, type of dominant burning material and the activation time of Smoke Management Systems (SMS) fans all influence tenability times within the tunnel. It is suggested that all these factors must be considered in the performance-based fire safety design and the accident management of a tunnel.
SUMMARYExperimental and theoretical investigations were conducted on the combustion behaviour of compacted, rendered straw bales exposed to two radiant heat flux regimes-(1) 30 kW m −2 for 30 min and (2) 50 kW m −2 for 40 min. The objective was to examine the fire safety of the rendered straw bales, which are used to construct houses in rural areas or on the urban fringe. The rendered bales were ∼ 950 mm× 450 mm×550 mm in size, comprising a ∼ 45 mm thick render layer on all sides. Two types of render materials-earth-based and lime-based-were tested. The 30 kW m −2 , 30-min regime resulted in little damage to the render layer and no combustion of the straw bale. The 50 kW m −2 , 40-min regime initiated combustion of the straw 24 h after the end of the exposure regime, consuming the entire straw bale over 11 days.A two-dimensional mathematical model describing the heat transfer through the render and the straw, and the combustion of the straw is presented. The kinetic parameters for the pyrolysis and combustion were derived from thermo-gravimetric analysis of the straw. The physical and thermal properties of the render and the straw were obtained from measurements and literature. The model predicted transient temperature profiles within the straw bale. The trends of predicted temperatures compare favourably with the experimental measurements, although aspects of the theoretical predictions of the ignition of the straw could not be reconciled with experimental results. q Commonwealth of Australia 2008.
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