7.1. Emergency exits
Emergency exits are provided in all except the shortest tunnels to allow tunnel users to evacuate on foot from the traffic tube to a place of safety in an emergency. In short tunnels, the portals are adequate as emergency exits. In most tunnels, however, additional emergency exits are required in order to limit how far tunnel users have to travel to reach a place of safety.
Emergency exits may be provided in different ways, including:
- Cross-connections or cross-passages between tubes (which may be used by vehicles as well as pedestrians).In some cut and cover tunnels, the cross-connection may simply comprise a single doorway between the tubes.For bored tunnels, the tubes are usually spaced some distance apart, and cross passages (of a measurable length) are created.
- Exits may lead into shelters where the public can remain safely during an emergency. However these shelters have to be connected to the surface directly or by an escape gallery, in order to make possible in a second stage the escape under the control of the fire brigade. Shelters are specially equipped enclosures with a separate special fresh air supply and an emergency telephone. Some welfare facilities may be provided. The psychological effects associated with the use of shelters should be considered in the design and the procedures for their use (see Report 2008R17 "Human factors and road tunnel safety regarding users" ).
- Safety galleries (passages) constructed alongside the traffic tubes or perhaps under the carriageway and leading to the surface or other safe place.
- Escape passages leading directly from an emergency exit doorway to the surface or other safe place.Such passages are generally feasible only for tunnels with little cover (cut and cover tunnels for instance).
Figure 7.1-1 shows a typical escape pattern for a uni-directional tunnel with longitudinal ventilation.
The appropriate spacing between emergency exits depends on:
- types of vehicles using the tunnel, which dictates the nature of incidents that could occur;
- traffic volume and the number of tunnel users that may need to use the exits;
- the capability of tunnel ventilation system to maintain tenable conditions for evacuation in the tunnel;
- incident detection and warning systems;
- the nature of the protected routes beyond the emergency exits (including their dimensions and the presence of significant gradients or stairs); and
- human behaviour.
The optimal distance between two emergency exits is generally estimated to be between 100 and 500 m.
The following design principles are important:
- emergency exits should be clearly signed as such to distinguish them from equipment room access. The recommended colour of the doors (very often the "emergency exit" colour green) must be considered in combination with the type of tunnel lighting;
- doors and openings should be sized to handle a large number of people in a short time as well as the passage of rescue workers with equipment or stretchers;
- emergency exits should be visible either directly or by visible and recognisable signs from any position in the tunnel;
- the luminance of access floors, doorsteps, etc. and the room just behind the emergency exit should be "inviting" and be designed to prevent people from falling or stumbling;
- curb lighting/markers should not be obstacles for walking people;
- emergency exit doors should not be locked.
Figure 7.1-2 shows a possible design of an emergency exit.
Further discussion of emergency exits is provided in the Technical Report 1999 05.05.B "Fire and smoke control in road tunnels" and, in more detail, in the more recent Technical Report 2007 05.16.B "Systems and equipment for fire and smoke control in road tunnels".