A model of a tunnel fire is proposed to describe the behavior of the fire gases spreading in
opposite direction to a fresh air current induced by tunnel ventilation. In particular, the model
yields an analytic formula for estimating the critical ventilation velocity, which is required to
prevent backlayering, i.e. to arrest the fire gases close to the fire source. It can be shown that
the critical ventilation velocity mainly depends on the heat-release rate of the fire and the
height of the tunnel. An important finding, already suggested by other theories, is that for
large heat-release rates the critical velocity does not depend on the heat-release rate. The
model has been validated by comparison with the experimental data obtained from fire tests in
an instrumented tunnel. The formula of the critical ventilation velocity, which is also given in
dimensionless form, is generally applicable for ventilation rates and heat-release rates
occurring in real tunnel fires. r 2002 Elsevier Science Ltd. All rights reserved
A model of a tunnel fire is proposed to describe the behavior of the fire gases spreading inopposite direction to a fresh air current induced by tunnel ventilation. In particular, the modelyields an analytic formula for estimating the critical ventilation velocity, which is required toprevent backlayering, i.e. to arrest the fire gases close to the fire source. It can be shown thatthe critical ventilation velocity mainly depends on the heat-release rate of the fire and theheight of the tunnel. An important finding, already suggested by other theories, is that forlarge heat-release rates the critical velocity does not depend on the heat-release rate. Themodel has been validated by comparison with the experimental data obtained from fire tests inan instrumented tunnel. The formula of the critical ventilation velocity, which is also given indimensionless form, is generally applicable for ventilation rates and heat-release ratesoccurring in real tunnel fires. r 2002 Elsevier Science Ltd. All rights reserved
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