The Importance of Fire Safety in Tunnel Design

Fire safety, protection and prevention are an ever increasing part of tunnel design as regulations tighten and technology advances in detection and control and management systems. Intensive research is undertaken into the effects of fires in tunnels, the evacuation of passengers, smoke ventilation and fire control.

Several factors can have an effect on the fire growth and the potential danger to passengers and damage to the tunnel. The behaviour of people using the tunnel, the tunnel design and layout, the structure and make up of vehicles within the tunnel, the equipment and safety systems installed in the tunnels, the quality of maintenance of the tunnel and the reaction of the emergency services all play a part in fire safety. While the tunnel design itself cannot control or account for all of these factors, it is essential to have an understanding of them and their relationships with each other, to create the safest possible design.

Safety and Risk Management
A full and exhaustive risk assessment should be undertaken on each specific project, as well as overall in the development of tunnelling to improve knowledge and experience of fire safety. The over-riding aim is to reduce the risk of fire, in terms of the frequency of fires occurring, and reduce the consequences for people and for the tunnel structure itself.

An assessment can be broken down into four key areas: The safe evacuation of tunnel users, access for emergency personnel, equipment and vehicles, protection of the surrounding area of the tunnel, and protection of the tunnel structure. Fire detection and control systems should be put in place along with passive and active fire protection systems. These should be fully planned from design stage and specified for the project; each tunnel is entirely different and blanket specification risks using methods or equipment which is not fit for purpose. 

Fire Testing in Tunnels
Research and testing into the behaviour and impact of fires in tunnels has been extensive and is ongoing throughout the world. Pictured below is a test carried out by SP Fire Technology in 2003, one of the leading institutes in tunnel fire research, simulating a fire in two HGV’s in a model scale test environment. The aim of the tests, which at the time were the largest performed in a tunnel, was to assess the heat release rate, the fire development and the flame spread, amongst other things. One of the main conclusions showed that the heat release and temperature was much higher than previously thought in this type of fire, e.g. heavy vehicles carrying normal goods.
  

Source: sp.se

Other tests have been carried out to assess the smoke spread and concentration, the efficiency of thermal ventilation shafts, the effect of ceiling height and wall and ceiling temperatures, the impact of suppression systems, and several other factors. The result is that we know more than ever about the effects of fires in tunnels and this aids regulation and technological advancement in detection, management, and control.

Research and development continues, and fire testing will play an important role in changing tunnel design in the future. Testing institutes are beginning to use computer simulated 3D models to reproduce fires and the statistical analysis drawn from these models further enhances our understanding of the behaviour of fires in tunnels.

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