Self-rescue describes the ability of people involved in a tunnel incident to get away from a source of hazard by their own initiative and appropriate behaviour. Experience from past tunnel fire incidents shows that smoke is the main problem for human safety in a tunnel fire. The opportunity to quickly reach a safe zone, which is not affected by smoke, is essential for mitigating the consequences of the incident. Hence the self-rescue principle is a key pillar of tunnel safety in case of a tunnel fire.
Fire in a modern building will normally give those in the building a reasonable opportunity to escape to a safe zone closely located from the area affected by the fire. In a tunnel, users have to escape to one of the portals to get outside of the tunnel. For long single-tube road tunnels without emergency exits to an escape route independent from the affected tunnel tube, a safe zone may be several kilometres away - often an unreasonable prerequisite for safeguarding the principle of self-rescue. Therefore modern tunnel guidelines include prescriptions for a maximum admissible distance of emergency exits leading to a safe zone, which can be an escape tunnel, an escape shaft, an exit to the open air or a parallel second tunnel tube. For instance, Annex I of the European Directive on minimum safety requirements defines a maximum admissible distance of 500m and national guidelines often define stricter requirements.
Serious incidents that challenge the self-rescue principle are fast-developing vehicle fires involving vehicles with a high fire load (mainly HGVs with combustible loads) which are able to produce a lot of smoke within a short period of time. However, a fire in a small vehicle can also turn into a larger fire, e.g. by involving several vehicles.
In any case, it is important to evacuate early and fast. Therefore, in addition to providing an emergency route to a safe place, measures are required to make sure people react quickly and evacuate early through the emergency exits.
A closer look into the self-rescue process reveals that the evacuation behavior of people can be divided into several phases. At the beginning is the pre-evacuation phase, which includes all events before the start of the evacuation and ends with the decision to escape. In the subsequent evacuation phase, we can distinguish the pre-movement phase and the movement phase. During the pre-movement phase, the tunnel user searches for information and selects an escape route. The movement phase includes all behavior that tunnel users display during the evacuation until they reach an escape target.
Hence, it is important to support this procedure by providing relevant information and giving clear instructions to people - visually or acoustically.
Further, self-rescue may be influenced by tunnel parameters and traffic conditions. For instance, there is a close link between self-rescue and smoke management strategies.
In tunnels with two tubes operating with unidirectional traffic and longitudinal ventilation, the ventilation typically supports smoke propagation in the driving direction (the initial direction of smoke propagation due to traffic-induced airflow). The smoke gradually affects the empty part of the tube in front of the incident. People that are stuck in traffic behind the incident can evacuate to the other tube and are normally not affected by the smoke. The second tube will normally be closed to traffic, and can be considered a safe zone to evacuate to. There is also a safe evacuation passage between the tubes. In unidirectional tunnels with regular congestion or in bidirectional tunnels the situation is more complex, as vehicles are likely to be blocked on both sides of the fire site; hence the interaction between self-recue and the strategy of emergency ventilation gets more complicated. However, modern risk assessment tools are able to investigate this process in detail for particular situations, thus providing valuable information for optimizing the interaction between human behaviour, procedures and technical equipment.
Furthermore, a steep evacuation route may also affect the ability to perform self-rescue as well as smoke propagation behaviour. Therefore, tunnels with high gradients require special attention.
Public education is important in providing knowledge and skills for self-rescue initiatives to road tunnel users. Information campaigns and publicity provided by road tunnel operators or authorities can help road-tunnel users understand the self-rescue measures to adopt when they encounter an emergency. In the context of self-rescue, special issues regarding people with reduced mobility have to be taken into account - see technical report 2008R17 “Human factors and road tunnel safety regarding users “
Many of these topics are also discussed in Section I "Objectives of fire and smoke control" of report 05.05.B, which includes a detailed discussion on tenability criteria under fire situations.