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Deluge System Operating Effectiveness in Road Tunnels and Impacts on Operating Policy


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Author M Bilson, A Purchase and C Stacey


The procedure for operation of deluge systems installed in road tunnels is
still a subject of debate. The work undertaken in this paper assists in the
understanding of the effects of deluge in road tunnels, and thus aims to help
inform the development of operational policy.

Analysis was undertaken using computational fluid dynamics (CFD) simulations
to help explore the deluge interaction with the tunnel ventilation (including
smoke exhaust) and combustion products. It was found, for the scenarios
considered, that:

  • Deluge activation can decrease the required critical velocity for smoke
    backlayering, and this in turn can improve the effectiveness of a smoke exhaust

  • The dominant parameter for deluge
    effectiveness is the vehicle configuration, with shielded scenarios (such as a
    fire in the passenger compartment) showing almost no water reaching the fire.
    The water delivery rate (5 mm/min versus 10 mm/min) has only a minor effect on
    the smoke duct damper inlet temperatures and downstream smoke temperatures for
    small fires (5 MW). For large fires (50 MW) the higher water delivery rate
    gives slightly improved performance (lower damper inlet temperatures and lower
    downstream smoke temperatures).

A one-dimensional transient tunnel model incorporating different operational
and deluge response policies (ie deluge activation times) was developed. It was
used to examine the influence of different operational parameters on life safety
risk and tunnel damage risk. It was found, for the scenarios considered,

  • The life safety risk for different
    scenarios has a sensitivity to deluge activation policy with the case of
    delaying the deluge activation for a long time giving the worst outcomes.
    However, the most critical parameters for life safety risk are operator
    response time (for all response activities, not just deluge) and the type of
    fire (configuration, size and growth rate).

  • There is a reduction in risk of tunnel
    damage when the deluge is activated earlier, although the fire configuration
    (ie whether or not the seat of the fire can be reached) has the greatest
    influence on the outcome.

It is concluded that the deluge activation policy should be case-dependent. It will depend on the tunnel, the safety
systems provided, and most particularly the vehicles involved. The current
policy in Australian tunnels is for manual activation of the deluge by the
tunnel operator as soon as practical after the fire is confirmed (see also
PIARC, 2007). This is a good policy. However, future work may be helpful to
improve the skills of operators to make the best judgement as to when deluge
should be activated, balancing all risks. This work could include research to
further the understanding of deluge and fire in road tunnels, training programs
and consideration of historical fire events.