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

Abstract

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 small-scale tunnel fires to quantify the influence of heat release rates and tunnel height. We define two non-dimensional 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.