Let us look back at the problem introduced in Section 1.3.1. A risk analysis is to be carried out to predict the effect of various alternative safety measures for a road tunnel. The analysis, together with other relevant information, will be used as the basis for the decision-making concerning what measure(s) to implement.
7.1.1 Problem definition
What are the consequences of a ventilation system not being able to handle a 100-MW fire? The aim of the fire ventilation system is to ensure that the smoke gases are forced away from the fire site and directed further inwards into the tunnel section, in the direction of traffic flow. For a dual carriageway tunnel, this is advantageous as the drivers situated downstream of (past) the fire site will exit the tunnel without even being aware of the existence of the fire. The cars that are located upstream of (before) the fire site will have to stop when they encounter the fire or smoke, thus forming a queue. In such a situation, it is important to force the smoke gases further inwards into the tunnel and thus avoid the situation whereby the drivers stationary in the queue upstream of the fire are exposed to smoke gases before they can evacuate on foot out of the tunnel or through the cross galleries (emergencyexits).
The case is based on a tunnel that is almost horizontal. There is a slight rise in one carriageway and a slight fall in the other carriageway. Because warm air is ...