Road Tunnels Manual

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2.5. Principles and tools for fire safety

Among the possible risks to be considered in road tunnels, vehicle fires give rise to particular concern because they are not very rare events and their consequences may be far larger underground than in the open if no appropriate measures are taken. For this reason, several PIARC reports treat the issue of fire safety in road tunnels.

Part of the material included in these reports relates to specific tunnel features and is dealt with in the corresponding chapters of this manual, for instance:

However, before fire-safety measures can be defined, general principles, basic information on tunnel fires and study methods must be available. These are the issues dealt with in this section.

On the basis of the general safety objectives for road tunnels stated in Section General principles above, more precise aims have been proposed for fire and smoke control:

  • to save lives by making self evacuation by users possible,
  • to make rescue and fire fighting operations possible,
  • to avoid explosions,
  • to limit damage to tunnel structure and equipment and to surrounding buildings.

These objectives are 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. Complementary guidance is included in Section 2 "Safety concepts for tunnel fires" of report 05.16.B.

In order to help assess the risk and provide data to be used as a basis for design, information on the charateristics of tunnel fires, relevant influencing factors, as well as frequency and severity of fire incidents are given in Chapter 4 of the report “Experience with Significant Incidents in Road tunnels".

An understanding of how smoke behaves during a tunnel fire is essential for every aspect of tunnel design and operation. This understanding will influence the type and sizing of the ventilation system to be installed, its operation in an emergency and the response procedures that will be developed to allow operators and emergency services to safely manage the incident. Detailed discussion on the topic can be found in Section III "Smoke behaviour" of report 05.05.B and Section 1 "Basic principles of smoke and heat progress at the beginning of a fire" of report 05.16.B, which analyse in detail the influence of different parameters (traffic, fire size, ventilation conditions, tunnel geometry) in the development of an incident.

To help scientists and designers, an exhaustive description of basic (full and small scale experimental results) and advanced (computer simulation) techniques available to approach fire safety studies is given in Section IV "Study methods" of report 05.05.B.

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