Paper presented at the 3rd International Symposium on Tunnel Safety and Security

Water mist systems are unable to suppress or control large fires, therefore the ‘design fire’ for a water mist system in a tunnel should not be specified in terms of peak heat release rate, but rather in terms of the characteristics of a growing fire which such a system is designed to suppress. This paper reviews the growth rates of a number of fire experiments carried out in tunnels and makes observations regarding the influence of tunnel ventilation on these growth rates. Further experiments will be required to validate these observations. It is suggested that tunnel ventilation of the order of 3ms-1 may provide the optimal conditions for rapid fire growth and that both higher and lower airflows may result in slower growing fires. Three ‘design fires’ for water mist systems are proposed.