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

• Published in: Tunnelling and underground space technology 2021-06, Vol.112, p.103853, Article 103853
• Main Authors: Khattri, S.K., Log, T., Kraaijeveld, A.
• Format: Article
• Language: English
• Subjects: Critical velocity; Critical ventilation velocity; Data analysis; Fire protection; Fire safety; Heat; Heat release rate; Heat transfer; Mathematical models; Simulation; Studies; Tunnel fires; Tunnel ventilation; Tunnels; Velocity; Ventilation
• ISSN: 0886-7798; 1878-4364
• DOI: 10.1016/j.tust.2021.103853

•The work develops a simple yet powerful new model for critical ventilation velocity.•The new model offers notable improvements over older models.•Contrary to the classical approach, the work uses a different strategy to develop the model.•The paper outlines a theoretical analysis to discover the parameters that control the critical ventilation velocity (Section 2).•The work verifies and validates the new model (Figs. 9, 10 and 11). 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.