Study on the effectiveness of fire suppression deluge systems in tunnels

Abstract

The required water flow for adequate deluge system operation during a tunnel fire is currently only prescribed by a few regulatory authorities. Car fires are commonly used as references when addressing water-based suppression; nevertheless, limited public information exists on the amount of water required for correctly suppressing a car fire and the thresholds by which the suppression systems fails to be effective. This paper aims at delivering key experimental outcomes to fill this gap in car tunnel fire suppression. The effectiveness of deluge sprinkler systems was investigated by performing a series of full-scale car fire experiments. These experiments were performed by symmetrically positioning a single car under a single sprinkler nozzle, with activation happening (i.e. the sprinkler going off) at a certain time from ignition (which defines the size of the fire), and carefully gauging the burning behaviour of the car fire. A single car was used as it was deemed as the minimum unit for a fire. Temperatures inside, around, and above the car were measured and infrared camera footage was used to gauge flame heights during the experiment. Results from this study yielded two forms of car fire suppression by a deluge system: gradual and instantaneous. A correlation between heat release rate and required water flow for the deluge system is also presented. Outcomes herein show that a water flow per unit area of 6.6 mm/min is the minimum water flow required to effectively reduce the temperature in the immediate vicinity of a car fire of different sizes.