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10 CHAPTER TWO TUNNEL SAFETY PROJECTS--LITERATURE REVIEW OVERVIEW OF RECENTLY COMPLETED 4. Hazardous material tank truck accidents resulted in AND ON-GOING TUNNEL SAFETY PROJECTS cargo being spilled in 8.5% of the accidents. 5. The cargo was involved in 87% of the fires involving There are a number of recently completed and on-going proj- hazardous material tank trucks. ects on tunnel safety and design for tunnel fires in the United States and Europe (see Figure 1). Each project addresses dif- This information was used to calculate a hazardous mate- ferent components of design practice for tunnel fires. Results rial tank truck fire frequency for highway tunnels. The of these projects findings are documented in this chapter. FHWA report states that: The average tanker truck accident frequency was 4.91 PREVENTION OF TUNNEL HIGHWAY FIRES accidents per million miles (3.05 accidents per million Prevention and Control of Highway Tunnel Fires (FHWA- kilometers). RD-83-032): The principal investigator interviewed 18 Assuming that 8.5% of the accidents resulted in spilled U.S. agencies operating 35 vehicular tunnels for this study. cargo, the number of cargo spills per million miles was Responses from single agencies operating more than one estimated at 0.418 (4.91 accidents per million miles times 0.085 cargo spills per accident equals 0.418 cargo tunnel (such as the Pennsylvania Turnpike Commission) spills per million miles or 3.05 accidents per million kilo- carry more numerical weight than others that operate one. meters equals 0.259 cargo spills per million kilometers). The numbers illustrate the range of opinions, practices, and Assuming that 2.9% of the accidents involving tank systems encountered. This FHWA publication (7 ) states trucks result in fires, the number of fires per million that: miles of tank truck travel are estimated at 0.142 fires per million miles (4.91 accidents per million miles times 1. Trucks, in general, have an accident frequency that 0.029 fires per accident equals 0.142 fires per million ranged from 6.89 to 7.50 accidents per million miles miles) or 0.088 fires per million kilometers. (4.28 to 4.66 per million kilometers) from 1976 through Assuming that 87% of the tank truck fires involve the 1981. In comparison, tank trucks had an accident fre- cargo, the cargo fire frequency is estimated at 0.124 cargo quency that ranged from 3.97 to 5.98 accidents per mil- fires per million miles (0.142 fires per million miles times lion miles (2.47 to 3.72 per million kilometers) for those 0.87 cargo fires per fire equals 0.124 cargo fires per mil- same years. It was noted that tank truck operators may lion miles) or 0.077 cargo fires per million kilometers. have a more favorable accident history than general truck operators. The fire and hazardous cargo spill frequency for the Ref- 2. Few truck accidents resulted in fires (1.7% of all erence Tunnel are predicted by using these frequencies (7 ): truck accidents). Hazardous material tank trucks had a 70% higher fire-to-accident ratio than the general 1. One cargo spill per 2,390,000 tunnel crossings. trucking industry, with 2.9% of all accidents result- 2. One cargo fire per 8,064,000 tunnel crossings. ing in fire during the period from July 1966 through December 1968. Assuming that hazardous material tank truck crossings 3. Approximately 50% of the reported fires were caused occur at the rate of 100 crossings per day (36,500 crossings by collisions. The remaining 50% were caused by non- per year), the hazardous material fire and spill frequencies collision type accidents, such as overheated brakes or are predicted as (7 ): tires, defective exhaust systems, and defective electri- cal systems. Control of hazardous material tank truck 1. One cargo spill occurring every 65 years. tunnel crossings may reduce the probability of colli- 2. One cargo fire occurring every 221 years. sion accidents and subsequent fires. However, inspec- tion of hazardous material tank trucks before tunnel The incident frequencies for other tunnel lengths or for a dif- crossings also appears to be needed if the anticipated ferent number of hazardous material tank truck crossings may fire frequency is to be reduced appreciably. be calculated in a similar manner.