Abstract of Meeting Paper

Society for Risk Analysis-Europe 1997 Annual Meeting

Risk Comparison of Options for Safe Operation of a UK Road Tunnel. S. M. Hockey, W. G. Hulbert and S. K. Liew, WS Atkins Consultants Limited, Woodcote Grove, Ashley Road, Epsom Surrey, KT18 5BW, UK

A study has been carried out to support decisions on dangerous goods transport restrictions through a motorway tunnel in the UK. The aim of the study was to determine the likelihood and consequences of an accident occurring in the tunnel involving dangerous goods under various tunnel operating conditions: namely,

1. normal operation (unenforced prohibition of dangerous goods)
2. normal operation (enforced prohibition of dangerous goods)
3. normal operation (no prohibition of dangerous goods)
4. contraflow situation under normal operation (unenforced prohibition of dangerous goods)

The first step in the analysis was to ascertain the quantities and variety of dangerous goods passing through the tunnel under normal operating conditions (as in 1 above). With the cooperation of the police, a survey was designed and undertaken for three separate eight-hour periods, concurrently with a traffic count survey. In addition to an appreciation of the types of goods transported, the results of the two surveys enabled an indication of the modes of transport of dangerous goods through the tunnel to be gained. It was found that the danger of the goods transported was their flammability.

The next step was to ascertain the frequency and consequences of an accident involving dangerous goods occurring under normal operating conditions. This was undertaken using tunnel specific data and statistics from other tunnels throughout Europe, together with the knowledge gained of the characteristics of the goods passing through the tunnel and the incidents which occurred in the tunnel over a period of several months. The outcomes of this analysis gave an indication of the risk of various incidents in the tunnel per year.

From this baseline figure for risk, the risk of either altering the tunnel operating conditions (in the case of conditions 2 and 3) and the risk of contraflow situations was considered. It was found that conditions 1 and 3 presented the same degree of risk to tunnel users, that condition 4 did not add significantly to the risk and that condition 2 would result in reduced frequency of fire incidents, but the consequences of a fire would not necessarily be reduced. The risks due to other types of incident related to dangerous goods transport should be removed if operating condition 2 were enforced.

The study findings were used to determine the policy for future operation of the tunnel.

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