Risk
Comparison of Options for Safe Operation of a UK Road Tunnel
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.
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