Development of a risk assessment method for fire in rail tunnels

In the field of rail tunnel fire safety the concept of risk analysis plays an important part in the creation of a fire safety design that meets the objectives of the different stakeholders. For rail tunnels, there is very little information available about how to perform a quantitative risk assessment. Therefore, research on this topic has been conducted in order to develop a risk assessment methodology able to quantify the risk for people present in a tunnel. The problem is approached by means of an extensive literature study in which the deterministic cause of fires in tunnels is investigated. From this, the major contributing factors leading to disastrous events are determined. Next, a bow-tie structure was chosen for representing the risk assessment model. For the construction of the event tree part of the bow-tie, a closer look is taken at past accidents. From these experiences, the most important factors are determined to be: Human behaviour, fire growth curve, ventilation conditions, safety systems and population distribution. These factors are incorporated into the event tree by using pathway factors. After determining these factors, the frequencies are calculated for each branch outcome. The data obtained for these frequencies is based on European research projects, fault tree analysis and engineering judgement. For the determination of the consequences, the method is assisted by three integrated models: The Smoke spread, Evacuation and Consequence model. The models can take all types of geometry and materials, human behaviour and different susceptibilities of people for smoke into account. Together, they determine the possible number of fatalities, by means of a FID value, in case of a fire in a rail tunnel. The final risk is presented by the expected number of fatalities, the individual risk and the societal risk. The societal risk is demonstrated through visualisation of an FN-curve.