In his letter, Neil McCallum (NCE 8 November) asked when tunnel engineers are going to incorporate sprinkler systems in tunnels. This issue remains a topic of much debate at international tunnel safety and tunnel fire conferences.
The present recommendations of PIARC (the World Road Association) are that automatic sprinkler systems must not be used in road tunnels, and that if sprinklers are installed in a tunnel they must not be operated until everyone has been evacuated.
The reasons for this are that sprinklers are ineffective at extinguishing vehicle fires, that water can cause explosion in petrol and other chemical spillages, that visibility in the tunnel will be reduced due to destratification of the smoke and that vaporised steam itself can be a problem.
As a consequence, sprinklers are not considered to be useful for life safety, only for protection of the tunnel facilities after evacuation has taken place.
Ricky Carvel, research associate - tunnel fire dynamics, civil and offshore engineering, Heriot-Watt University, civroc@civ. hw. ac. uk