Tunnel Fire Dynamics as a Function of Longitudinal Ventilation Air Oxygen Content

Abstract

Longitudinal ambient air ventilation is the most common methodology for maintaining an amicable environment in tunnels during normal operations while providing an evacuation path during tunnel fire emergencies. The present work investigates the influence of forced ventilation air oxygen concentrations on tunnel fire dynamics. Mixing inert gasses such as nitrogen, argon, or carbon dioxide with ambient air changes the ventilation air oxygen concentration. In order to quantify the influence of the oxygen content on the critical tunnel safety parameters, multiple computational fluid dynamics (CFD) simulations were done on a reduced-size tunnel while preserving the system Froude number. Analytical expressions were developed to describe the importance of oxygen content on the tunnel fire dynamics. By employing Froude scaling, the resulting relations were extrapolated to real scale tunnels. For the ambient air ventilation, the extrapolated expressions displayed good agreement with experimental literature data. By adjusting the oxygen concentration, parameters such as maximum tunnel ceiling temperature, fire growth rate, maximum heat flux to the tunnel floor, maximum flux on the tunnel ceiling, and maximum heat release rate can be controlled. This is the case also for oxygen levels where people can survive. This may increase the possibility for evacuation and improve the conditions for firefighting, significantly improving tunnel fire safety.

Prediction of Tunnel Face Stability Using a Naive Bayes Classifier

“…Based on the above study, several conclusions can be drawn: Consequently, the 2nd naive Bayesian classifier is recommended for initial predictions of tunnel face stability. A number of predictions can be readily conducted using Equations (7) and (8) based on…”

“…At the construction stage, encountering face collapse is very likely for the tunnels driven in weak ground, such as clay [1], silt, and sand [2,3], and for tunnels with large cross-sectional area [4]. The collapse of the tunnel face threatens the safety of workers, equipment, and adjacent structures, including buildings, bridges, piles [5], underground pipelines, and existing tunnels [6,7]. Design work on the tunnel face involves the evaluation of its stability, the choice of reinforcement measures and the determination of related parameters [8][9][10].…”

A Numerical Study for Assessing the Risk Reduction Using an Emergency Vehicle Equipped with a Micronized Water System for Contrasting the Fire Growth Phase in Road Tunnels

“…CFD modeling was carried out in our study for simulating tunnel fire scenarios, certain applications of which can also be found more especially in Caliendo et al [18][19][20], and Khattri et al [21]. CFD modeling is based on the finite volume method for discretizing the tunnel in elementary cells, each cell is then solved by using the fundamental equations (i.e., conservation of mass, momentum, and energy) coupled with physical models describing the combustion, turbulence, and thermal radiation phenomena.…”

Numerical Investigation of the Required Quantity of Inert Gas Agents in Fire Suppression Systems

“…In fires, all halocarbon agents produce decomposition products which may represent a threat to the health and safety of the occupants. Inert gas agents suppress fires by diluting the oxygen concentration to a specific threshold level below which the fire flames are suppressed [5][6][7]. Research shows that lowering the oxygen concentration in air to below approximately 12% by volume will extinguish flaming fires [2,8].…”