Fire risk of heavy vehicles in high gradient road tunnels

The report examines the relationship between high gradients in road tunnels and the risk of fire in heavy vehicles. Our analyses show that the fire risk increases most from a gradient of 7 per cent, and we regard a maximum gradient of 7 per cent as a "breaking point". The length of high gradient distances is also related to the fire risk. The longer distances with a high gradient, the more fires there are in the tunnel. This applies both to gradients from 5 per cent and especially to gradients from 7 per cent. Subsea road tunnels have a higher risk of vehicle fires than other tunnels. This can mainly be explained by the fact that they have long and steep gradients. The cause of heavy vehicle fires in long and steep tunnels is primarily technical problems (overheated engine). Insufficient vehicle maintenance is often an underlying cause. The most relevant measure to prevent fires in heavy vehicles in Norwegian road tunnels is to not build long and steep road tunnels, whenever it can be avoided. The other most relevant measures that we identify in the study seem to be technology for automatically extinguishing fires in engine compartments, vehicle maintenance, technical inspections of vehicles, thermo portals and cooperative ITS.