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The Use of Risk Analysis to Achieve Consistency in the Fire and Life Safety Design of Road Tunnels


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Author L Poon


According to the Australian Bureau of Statistics, fatalities from road
transport accidents represented an average of over 97 per cent of all transport
related accidents between 1997 and 2002. With increasing traffic density,
tunnels are becoming a more viable means of providing alternative travel routes
to ease areas of congestion in the road transport network. However, unlike open
road conditions, a fire incident in the confined space of a tunnel environment
may impact upon many users that are remote from the incident location. In this
context, designing for an appropriate level of safety in tunnels is therefore an
important consideration for achieving consistency in the life safety measures
for users of the road transport network. Unfortunately, like fire safety
engineering design for buildings, there are presently no clear measures in the
design processes to assess the adequacy of the design in terms of attaining the
level of safety implicated in the design objectives. This is partly due to the
indeterminate nature in which the design objective or the level of performance
measure is stated – the intent of the objective is relatively clear but the
measure of it is not. Another reason is the lack of a standardised procedure for
determining the critical design variables affecting life safety. This is
important to ascertain consistency in the use or adoption of the important
parameters for design.

This paper looks at the processes involved in the fire engineering design of
road tunnels that are currently practised. A review of the design processes for
fire safety in road tunnels is provided, which includes the range of fire
scenarios in a tunnel environment, the traffic flow and composition, the
relevant fire protection systems, the ventilation and smoke control system, the
egress provisions and the benefits of incorporating fire brigade intervention. A
simplified risk assessment approach is developed for a typical road tunnel to
assess and evaluate the impact of a range of design parameters on life safety.
Using a sensitivity technique, the important variables are then identified and
means of reducing design variations associated with them are recommended. The
technique may be further refined for use in the development of codes or
guidelines in order to develop a suitable means of deriving more consistent
design values, and hence achieve better consistency in the overall level of
safety in the design.