A Comprehensive Study on the Critical Ventilation Velocity in Tunnels with Different Geometries

• Published in: The International journal of ventilation Vol. 14; no. 3; pp. 303 - 320
• Main Authors: Kazemipour, Ali, Afshin, Hossein, Farhanieh, Bijan
• Format: Journal Article
• Language: English
• Published: Taylor & Francis 01.12.2015
• Subjects: aspect ratio; critical ventilation velocity; heat release rate; hydraulic diameter; longitudinal ventilation; tunnel fire; tunnel slope
• ISSN: 1473-3315; 2044-4044
• DOI: 10.1080/14733315.2015.11684088

Longitudinal ventilation is a common technique for smoke management during a fire accident within tunnels. In this paper, fire and smoke movement behaviour in longitudinally ventilated tunnels is investigated focusing on critical ventilation velocity. Firstly, critical velocity (V C ) is evaluated for different heat release rates and results are compared and verified with model scale experimental data. Secondly, two fire scenarios inside tunnels with different cross sections are arranged and the reliability of some existing correlations for V C is explored. Results illustrate that using a combined geometric scale rather than the traditional single length-scale ones results in better estimation of critical ventilation velocity. On this basis, a new correlation with a wider range of applicability utilizing tunnel hydraulic diameter and aspect ratio as a combined parameter is presented. The effect of tunnel slope on critical velocity is also examined and obtained data are implemented to modify the new suggested correlation. Finally, the validity of the proposed correlation to estimate critical velocity in full scale tunnels is explored.