VTT methods to improve fire safety in subterranean facilities

VTT has developed methods for the assessment of fire safety in subterranean facilities. The methods make it possible to check and harmonise the currently widely divergent underground fire safety requirements. Having uniform requirements will make it easier to estimate the costs of fire safety solutions designed for underground facilities and reduce the risk of accident in underground metro stations, public bomb shelters in recreational use and in underground parking facilities and maintenance tunnels.

Simulation of the spread of smoke caused by a burning car in an underground car park. Source: VTT

Applying the state of the art fire safety assessment methods, VTT has examined the fire safety of an underground metro station in Helsinki, an underground parking facility, a bomb shelter and a maintenance tunnel in joint use. The results show that the fire safety design is mostly based on correct but partly also on uncertain estimates of smoke ventilation, fire spread, people's chances of escaping from the building and rescue operations in the event of fire.

At present no building permission is even required for constructions which are entirely underground. There is moreover considerable variation in the fire safety requirements imposed by municipal officials. Thus fire safety arrangements differ greatly, causing a great deal of overlapping work for both officials and designers.

In Helsinki there are nine million cubic metres of subterranean construction, 100 times the size of the Parliament building, and 250 kilometres of subterranean tunnels. Building underground saves energy and is increasing rapidly, in Finland and in China, for example. Elsewhere in Europe relatively more roads and railways have been built underground.

As far as fire safety is concerned, the major problems with underground spaces compared to those built above ground are that, in case of fire, the fire, the smoke and the people all try to go in the same direction – upwards – and that in a subterranean space the temperature will rise extremely high as the heat energy cannot escape into the external atmosphere. The first few minutes after the start of the fire are decisive for people escaping and getting into the fresh air, as the poor visibility caused by smoke may cause them to lose their way to the exits. Heat and poor visibility moreover impedes the rescue work of smoke divers.

VTT, in five years of cooperation with the National Institute of Standards and Technology, U.S., has developed a simulation technique for fire and evacuation of people. On an ongoing follow-up project a guide to the design of fire safety in subterranean spaces is to be composed based on the VTT findings.

The VTT research is funded by VTT, the Finnish Work Environment Fund, the Ministry for the Environment, the Ministry of the interior, the Ministry of Defence and Fläkt Woods.

Further information:

Photo: VTT
VTT Building and Transport Simo Hostikka, Research Scientist Tel. +358 20 722 4839 simo.hostikka@vtt.fi	City of Helsinki Marko Järvinen, Regional Fire Chief Tel. +358 50 541 8459 marko.jarvinen@hel.fi