Fire hazards in tunnels pose a serious threat to human life and can cause substantial financial losses. The increasing world population leads to an increase in mobility which accelerates the growth of traffic. High-performance fire and blast protective tunnels are therefore crucial.

The protection of tunnels can be established by installing fire rated doors with blast and smoke resistant capabilities. In this article I will explain how the dynamics of a tunnel are during a fire and how people and the structures can be saved by fire rated doors.

Fire protection in tunnels is important for the following reasons:

• It ensures life safety during fire events;
• It ensures operability of the tunnel structures;
• It ensures that there are no economic or financial losses.

Tunnel fire dynamics

A tunnel is an enclosed structure where fire and smoke cannot mix with open air. This situation is especially dangerous because fire can spread rapidly in certain directions whilst creating smoke. Consequently, oxygen levels within the tunnel decrease and people who are present will have a hard time breathing. Next to this aspect, people are also exposed to high temperatures due to the flames. In small tunnels, this situation is worse due to the fact that there is less oxygen present. The evacuation time and the possibility of fire containment is dependant on the tunnel size, larger tunnels allow for more evacuation time and higher possibility of fire containment.

The following safety measures can be taken to reduce the impact of fire:

• Safe escape route design;
• Installed smoke extraction systems;
• Install architectural products with fire and structural integrity, e.g. a fire door.

Fire rated doors in tunnels: a lifesaving solution

Fire rated doors in tunnels have to prevent the spread of fire, hot gasses and smoke from the main tunnel to other compartments. In general, fire rated doors are installed to provide access to escape routes and to protect people who have succesfully accessed the escape rooms/areas of the tunnel.

Smoke resistance and thermal insulation are key characteristics which need to be considered for fire rated doors to prevent smoke passage and heat transfer from the fire. Furthemore, corrosion resistance should be taken into consideration as well since aggressive and polluted chemicals are released from vehicles.

Since fire events in tunnels are different to fires in open air, the internationally recognized RWS curve is recommended to be used in order to test fire doors. The failure criteria for the RWS curve is that the temperature of the door reinforcement should not exceed 250 ^oC and the interface between the fire protection and the concrete should not exceed 380 ^oC.

Fire safety in tunnels is key to protect people and materials from the dangerous effects of fires. The side effects of high temperatures and high levels of smoke also need to be taken into consideration when assessing the risk within a tunnel. Fire rated doors are an excellent solution in providing sufficient safety for people and allow for efficient evacuation.