Presentation report (10/05/06)
It has been decided not to mandate the installation of sprinklers. The reasons are as follows:
1. Sprinklers cool the smoke causing it to descend and engulf passengers endangering their lives.
2. The sprays reduce visibility. The loss of visibility is exacerbated by the cooling of smoke which causes it to descend. Loss of visibility could affect the ability of people to evacuate.
3. Sprinklers may generate steam causing volumetric expansion and greater movement of smoke. Compared with not using sprinklers, steam generation would result in increased temperatures over a greater distance from the fire.
4. Flammable liquids can float on the water released by the sprays causing fire spread and increasing the size of the fire.
5. The sprays can increase the risk of explosions arising from the vaporisation of unburnt fuel.
There is, however, a significant body of opinion that favours the use of sprinklers. A series of reasons taken from the paper “Fire suppression in road tunnels – Why it is needed: A fire brigade view” by Les Fielding, International Symposium on Catastrophic Tunnel Fires (CTF), Boräs, Sweden, Nov 20 -21, 2003 are as follows.
1. Provide protection and time for people in a tunnel to escape.
2. Control a fire in its insipient stages reducing the amount of heat and smoke.
3. Wash heavier soot particles out of the smoke.
4. reduce the potential heat output of the fire protecting the infrastructure of the tunnel and prevent the radiated heat from spreading the fire to other vehicles.
5. Continue to suppress the fire providing the necessary control measures to allow fire fighters to enter the tunnel ensuring a safer more tenable environment for carrying out fire fighting operations.
6. Protect the tunnel structure from the effects of fire and heat.
7. Protect the environment from exposure to the products of combustion that would be produced by a large uncontrollable fire.
Having given due consideration to the issues, the view of the SRT group is that case in favour of installation needs further scientific justification. There is particular concern over the risk of a descending smoke layer engulfing escaping passengers and an explosion involving vapour from unburned fuel. The SRT group does not, therefore,favour installation.