A novel representation of the critical ventilation velocity for mitigating tunnel fires

Critical ventilation velocity dominated research within the field of tunnel fire safety because it is integral for designing a tunnel ventilation system. This work proposes a novel analytical model for the critical ventilation velocity. The theoretical analysis infers that the heat release rate and tunnel height controls the critical ventilation velocity. Earlier studies support this conclusion. We perform several highly accurate simulations of smallscale tunnel fires to quantify the influence of heat release rates and tunnel height. We define two nondimensional quantities and identify a correlation through data analysis. The new model illustrates the transition where the critical ventilation velocity increases rapidly with the heat release rates however at higher heat release rates the critical ventilation velocity becomes constant. To verify and validate the model, we compare the novel formulae against the existing relationships and available experimental data. There exist numerous analytical models but several of these models are discontinuous while others do not capture the transition where the critical velocity becomes independent of the heat release rate. The novel relationship, presented in this work, eliminates these drawbacks.

Automated summary

This study introduces a novel analytical model for determining the critical ventilation velocity in tunnel fire safety, where the heat release rate and tunnel height are the key factors. By conducting highly accurate simulations of small-scale tunnel fires and analyzing data, a correlation between these two factors is identified. The new model shows the transition of critical ventilation velocity with heat release rates and establishes the critical velocity becoming constant at higher heat release rates.