A Methodology for Life Safety Assessment in Road Tunnel Fires

This paper presents a methodology for evaluating life safety risks in road tunnel fires. The methodology considers three realistic fire scenarios, smoke spread, occupant evacuation, and reliability of fire suppression systems. The three fire scenarios represent three variations of fire growth rates. The road tunnel in this study is assumed to have two traffic tubes, a longitudinal ventilation system and emergency exits and escape routes. The Fire Dynamics Simulator is used to model smoke spread and the time available for evacuation, based on a visibility limit when occupants cannot find their way to the emergency exits. A simple evacuation model is used to estimate the time required for people upwind of the fire to egress through the emergency exits. Vehicles downwind of the fire are assumed to continue moving and exit the tunnel safely. In two of the three fire scenarios, conditions in the tunnel become untenable rapidly, not allowing sufficient time for the people to egress safely. A simple risk assessment approach is used to estimate the number of fatalities, based on the number of occupants who are trapped in untenable conditions in the tunnel. The assessment shows that the level of fatalities depends very much on the reliability and effectiveness of the installed fire suppression system. It is argued that a rapid and reliable fire suppression system is critical in preventing heavy casualties in a tunnel fire.