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OCR for page 53
54 CHAPTER NINE DESIGN FOR TUNNEL FIRES--LITERATURE REVIEW BACKGROUND Safety equipment, such as heat detection of vehicles before entering the portals. Every tunnel is unique, making it difficult to generalize designs for road tunnel fires. As reported, design fires and design Preventive measures on fire in a tunnel are related to fire scenarios are essential inputs for a fire safety-engineered approach to fire safety design of new tunnels and any appraisal Removal of sources of ignition, of fire safety protection measures in existing tunnels. An Reduction of the likelihood of a fire, and effective fire protection design for life safety and property Prevention of the development from the ignition to a protection in tunnels requires a systematic assessment of a number of component "sub-systems," which contribute to severe fire. the overall safety of the design. These sub-systems are: Gasoline tankers are prohibited from using many U.S. The initiation and development of fire spread tunnels. Dangerous goods that travel through tunnels can be Spread of smoke and toxic gases costly in terms of human lives, tunnel damage, transport dis- Detection of fire and activation of active fire life safety ruption, and the environment. Conversely, needlessly banning systems dangerous goods from tunnels may create unjustified economic Tunnel users' evacuation costs and force transport operators to use more dangerous Fire service intervention. routes. Further complexity arises because the time scales for the The fire prevention measures presented in Table 11 can be response of active fire protection measures such as fire detection implemented in tunnels to reduce either the probability or the and safety systems activation are different from the response consequences of an incident in a tunnel. time of occupants during evacuation or the response time for structural integrity. The main engineering goals regarding the fire protection of road tunnels are listed here in order of priority, as identified The first priority identified in the literature for fire design in the literature: of all tunnels is to ensure: 1. Objectives related to life safety: 1. Prevention of critical events that may endanger human Minimize the risk of injury or death for tunnel users life, the environment, and the tunnel structure and in the event of a fire. installations. Minimize the risk for people outside of the tunnel. 2. Self-rescue of people present in the tunnel at time of In densely populated areas, people outside the tun- the fire. nel may also be affected by the fire inside the tunnel 3. Effective action by the rescue forces. (e.g., when buildings are present above the tunnel or 4. Protection of the environment. when dense and toxic smoke may cause secondary 5. Limitation of the material and structural damage. incidents on roads adjacent to the tunnel). Furthermore, part of the objective is to reduce the consequences Minimize the risk of injury or death for rescue teams and minimize the economic loss caused by fires. and repair workers. 2. Objectives related to economic consequences and to A 100% safety scenario against a tunnel fire is not possible; the quality of life: however, actions can be taken to reduce the risk to a reason- Avoid damage that threatens the tunnel construction. able minimum. Preventive measures are safety measures that Avoid the need to incur expensive repair work. reduce the probability of an unwanted event. Preventive Avoid long-term interruption of service. safety measures in tunnels can be related to: The proactive measures comprise all of the general actions Organization and traffic management; taken in the planning phase to improve tunnel safety-- Structural or geometrical solutions; and independently of a specific tunnel project.

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55 TABLE 11 RISK REDUCTION MEASURES CLASSIFIED ACCORDING TO THEIR MAIN PURPOSE Measures to Reduce the Probability of an Accident Related to tunnel design and maintenance Tunnel cross section and visual Alignment Maintenance design Lighting (normal) Road surface (friction) Related to traffic and vehicles Speed limit Escort Vehicle checks Prohibition to overtake Distance between vehicles Measures to Reduce the Consequences of an Accident Alarm, information, communication of operator, and rescue services Closed-circuit television Automatic fire detection Automatic vehicle identification Automatic incident detection Radio communication (services) Emergency telephone Communication with users Emergency telephones Alarm signs/signals Loudspeakers Radio communication (users) Evacuation or protection of users Emergency exits Lighting (emergency) Failure management Smoke control Fire-resistant equipment Reduction of accident importance Fire-fighting equipment Drainage Emergency action plan Rescue teams Road surface (non-porous) Escort Reduction of the consequences on the tunnel Fire-resistant structure Explosion-resistant structure Source: Safety in Tunnels (2001) (41). Legislative initiatives and other actions highlight the Fixed fire suppression systems can prevent fires from awareness of the problem and contribute to an improve- developing into severe fires, but could reduce visibility ment in the standards for designing and operating tunnels. in the tunnel. Research projects and similar actions that develop and The best chances of successful fire fighting are in the ini- disseminate knowledge about tunnel fires contribute to tial phase of a fire. Therefore, systems directed by operators future tunnel safety. or end users may be beneficial. Such installations are easy In addition, any proactive measures regarding user behav- to use because the tunnel's users will probably be unfamiliar ior such as an increase in awareness to safer driving and with fire fighting and with the tunnel's environment. correct behavior in the event of an incident may signifi- cantly influence safety in the tunnel. Response to Fire Mitigation measures are safety measures that aim to The fire resistance of doors and walls reduce the probability limit the consequences once the ignition has taken place of the development and spread of fires from one compart- ment to another. The fire resistance of the active fire life safety and developed into a fire. The mitigation measures may be systems (e.g., ventilation and fire suppression) ensures that related to: the development of the fire can be controlled. Reduction of the fire development, Reduction of Consequences to Humans Reduction of the consequences to humans, and Reduction of the consequences to structure and Structural Measures equipment. The highest priority of tunnel design safety is to mitigate consequences to humans. The geometrical layout of a tunnel Reduction of Fire Development can contribute to the mitigation of a fire. For example, it is easier to ensure that the majority of tunnel users have smoke- Structural Measures free conditions if the tunnel is operated in one-way traffic. Also, the cross-sectional area influences the chances of Flammable liquids may leak during or before a fire. A suitable creating smoke-free areas and providing conditions for drainage system reduces the quantity of flammable liquids escape from a fire. from the source of the fire and thereby mitigates a serious fire development. One of the most important mitigation measures for users exposed to a fire in a tunnel is the provision of escape routes. Safety Equipment Safety will be influenced by the spacing and design of the emergency exits. In some cases, the rescue and evacuation The main function of ventilation during a fire is to of the injured and physically disabled will have to be assisted control the smoke and, to some degree, influence the by the rescue forces, tunnel operators, etc. Emergency exits development of the fire. can serve as access routes for the rescue forces.