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25 2. Economic losses related to vehicles and goods, and the fire, they are difficult to suppress and extinguish and usually cost of repair of damage/reconstruction: receive more attention. Fire statistics indicate that highway Destroying tunnel equipment (e.g., lighting, ventila- tunnels are safer than open roads. tion, and telecommunication); Damage to the tunnel construction: the main effects When HGVs are involved in fires, there is a higher risk of are spalling of concrete, overheating of concrete rein- the fire developing into a much larger, serious fire. forcement, collapse of false ceilings, and ventilation The duration of recorded serious fires in road tunnels ducts; and Severe damage or loss of burning vehicles and their ranged from 20 min to 4 days. Most of the serious fires last from 2 to 3 h. goods. 3. Traffic disturbance resulting from closure or reduced Analysis of the catastrophic tunnel fire events provided service level of the tunnel after a fire (e.g., re-routing the following conclusions: resulting in extra transport time, direct economic losses, and possibly increased risk to the users). Fires develop much more quickly than expected. 4. Potential environmental damage from the fire. Fire temperatures in excess of 1000C (1832F) are achieved. In some cases, tunnel rehabilitation after fires can take Smoke volumes are higher than expected from an early weeks or months. During this time, traffic congestion on stage of the fire growth. the roads in the vicinity of the closed tunnel is an almost Fire spread between vehicles occurs over a much greater inevitable result, especially in densely populated areas. distance than had been expected previously. The road tunnel users behaved unexpectedly, such as: In two French tunnels in Lyon (Tunnel Fourviere and Did not realize the danger to which they were exposed. Tunnel La Croix Rousse) about 40% of the fires were extin- Failed to use the safety infrastructure provided for guished by a fire extinguisher (six cases). In about 60% of the self-rescue. events (eight cases) the help of a fire department was needed. Wrongfully believed that they were safer in their cars Most fatalities in road tunnels appear to arise from ordinary than if they used the self-rescue safety systems. traffic accidents. Norwegian data indicated that approximately Chose to stay in their vehicles during the early stages of two-thirds of deaths resulted from common traffic accidents a fire since they did not want to leave their property. and about one-third from fire-related incidents. In addition, it Realized too late the danger they had placed them- stated that "dangerous goods" incidents are likely to involve selves in, by which time it was too late to execute fire, which may be assumed to be about one-third of fire- self-rescue. related incidents (see Table 5). Collisions and other vehicle accidents are not the most Fire statistics indicate that highway tunnels are safer than frequent cause of fires, although most large fires are caused open roads. As far as can be determined, there have been only by accidents. three major tunnel fires in the United States. Small automobile Engine fires cause approximately two-thirds of bus fires. fires are frequent and occur as often as weekly in congested They can be the result of damaged fuel lines, oil lines, urban tunnels. To date, such fires have been extinguished or overheated HVAC systems. without difficulty. Electrical short-circuits, followed by a cable fire (the most frequent cause for light vehicle fires). Electrical SUMMARY fire or cable insulation was the item first ignited in 29% of the U.S. bus fires. Although major fires in tunnels (with a HRR of more than Twenty-seven percent of the bus and school bus fires 20 MW resulting in injuries, loss of life, and structural damage) began with the flammable or combustible liquids or are very rare events, because of the unique nature of a tunnel gases, piping, or filters. TABLE 5 LIFE LOSS IN ROAD TUNNEL INCIDENTS IN OSLO Potential Loss of Life per Type of Incident Billion Person-Kilometers Percentage (person-miles) Common Traffic Accidents 0.74 (1.19) 67 Fire, Light Vehicle 0.08 (0.13) 7 Fire, Heavy Vehicle 0.24 (0.39) 21 Fire in Tunnel Installations 0.01 (0.02) 1 D an gerous Goods" Incidents 0.04 (0.06) 4 Total 1.1 (1.77) 100 Source: Assessment of the Safety of Tunnels Study (23).

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26 Underseat heaters catching fire. 2. Economic losses related to vehicles and goods and cost Braking systems; these can overheat. of repair of damage/reconstruction: Collisions. Destroying tunnel equipment (e.g., lighting, ventila- Technical defects (self-ignition) of tunnel equipment. tion, and telecommunications); Maintenance work in tunnels. Damage to the tunnel construction: primary effects are spalling of concrete, overheating of concrete The risk of a vehicle fire tends to increase in situations of reinforcement, and collapse of false ceilings and intensified motor heating (steep uphill lanes of tunnels, tun- ventilation ducts; and nels after a long uphill slope) and intensified brake heating Severe damage or loss of the burning vehicles and (long downward slopes). their goods. 3. Traffic disturbance owing to closure or reduced service The main consequences of fires are: level of the tunnel after fire. 4. Potential environmental damage resulting from the 1. Fatalities and injuries to fire. Tunnel users, Operating personnel, and In some cases, tunnel rehabilitation after fires can take Rescue forces. weeks or months.