Modelling of water mist fire suppression systems by a one-zone model

Substantial progress has been made in studying water mist fire suppression systems (WMFSSs) in the past decade. As the one-zone model is commonly used for studying WMFSSs, this approach will be reviewed in this paper. This model is based on the experimental observation of water mists mixing with fire gas in a protected space and is developed for studying obstructed fire extinguishment in a compartment. The room is taken to be a homogeneous zone and the interactions between the fire-induced flow and the discharging water mists are studied. Conservation equations for the droplet phase and gas species in a fire compartment are solved to calculate the parameters describing the fire extinguishment. The effects of fire size, ventilation, pre-burning time, droplet size and discharging rate can be studied. The continuous discharge mode and cycling discharge mode of operating a WMFSS are described. The limitations of the one-zone modelling approach are also discussed. It is suggested that more experimental fire tests be carried out in order to explore the one-zone model further for practical design of the system.