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24 FIGURE 4 Burnley Tunnel (Australia) after fire. FIGURE 3 Mont Blanc Tunnel after fire. Other causes that were mentioned but occur far less frequently (long downward slopes). Also, for a short period of time included technical defects (self-ignition) in tunnel equipment during the opening of a new tunnel, there can be a tendency and maintenance work in tunnels. for more fire events as was observed in the Elb Tunnel in Germany. As the drivers become more familiar with a tunnel environment, the fire rate will stabilize at a lower level. FREQUENCIES OF TUNNEL FIRES In a French study representing 400 million kilometers (approx- CONSEQUENCES OF TUNNEL FIRES imately 250 million miles) run by trucks underground, HGV fires in 26 tunnels were analyzed and roughly classified accord- Fires generally produce heat, smoke, and toxic products, which ing to their importance to tunnel environment (Table 4) (21). can cause damage and loss of life. Heat is the cause of damage The heat release for fires classified as causing some damage to structure and installations, whereas it is rarely the original to the tunnel is estimated to be below 20 MW (68 MBtu/hr); cause of death. The threat to humans is primarily the loss of vis- serious fires are considered with heat release of more than ibility owing to smoke (which impedes evacuation), then toxi- 20 MW (68 MBtu/hr). Therefore, major fires are rare events, city. A secondary risk is that fires potentially represent a hazard even in relation to the entire number of truck fires in tunnels to the environment caused by the toxicity of the smoke and sub- (see Figure 4). German and Swiss data showed that only stances in the drainage. The main consequences of fires are: about 1 of 100 to 500 breakdowns is accompanied by a fire, with fire involved in about 1 of 10 to 20 accidents. Note that 1. Fatalities and injuries to: this information is currently being revisited by PIARC to Tunnel users, reflect the latest fire events. Operating personnel, and Rescue forces. The risk of a vehicle fire tends to increase in situations of Heat, smoke, gases, lack of oxygen, and loss of intensified motor heating (steep uphill lanes of tunnels, tun- visibility lead to intoxication, suffocation, burns, and nels after a long uphill slope) and intensified brake heating even death. TABLE 4 ESTIMATION OF FIRE RATES IN FRENCH TUNNELS Cases of Fire Classification of Fire for 108 veh x km (approx. 108 veh x miles) Passenger Cars Fires of any importance 12 (1.63.2) Trucks Without Fires of any importance 8 (12.9) Dangerous Goods Fires with some damage to the tunnel 1 (1.6) Very serious fires Estimation 0.1 to 0.3 (0.16 to 0.48) Trucks Transporting Fires of any importance Estimation 2 (3.2) Dangerous Goods Fires with involvement of the dangerous Estimation 0.3 (0.48) goods Source: PIARC (21).