Effect of Water Mist Nozzle Discharge Height on Fire Suppression Performance: A Review of Experimental and Numerical Studies

Dr. A. R. Sontake, Yuvraj Yadav, Ankit Kunwar, Nikhil Sharma, Kumar Satyam, Shiva Mall

Abstract: Water mist is a fine water spray in which 90% of the flow-weighted cumulative volumetric distribution of droplets (Dv0.90) is smaller than 1000 micrometres, and it has become an established alternative to conventional sprinklers and gaseous clean-agent systems because it combines a low water demand with an environmentally acceptable extinguishing action. It suppresses fire through combined mechanisms of gas-phase cooling, oxygen displacement, fuel-surface wetting and cooling, and radiant heat attenuation, allowing it to interrupt more than one side of the fire tetrahedron simultaneously. The height at which the discharge nozzle is installed above the fuel is a key design variable governing how effectively these mechanisms are mobilised at the seat of a fire, since it affects droplet trajectory, momentum loss before the droplets reach the flame, spray-cone dispersion, and the balance between direct fire suppression and ambient cooling of the protected space. Design practice, however, still leans heavily on test data generated at nozzle heights below roughly 3 metres and on single-fuel, fixed-height experimental programmes, even though real occupancies such as warehouses and tunnels often require much greater installation heights. This review synthesises five experimental and numerical (Fire Dynamics Simulator) studies covering a railway tunnel rescue station, a shielded diesel compartment fire, a shielded wood-crib fire in a partition room, a simulated warehouse compartment with nozzle height varied from 3 m to 9 m, and oil spray fires in confined spaces, examining how nozzle height interacts with operating pressure, flow rate, fuel type and shielding to govern suppression time, heat release rate and cooling performance. Across the reviewed literature, a consistent pattern emerges: lower or closer nozzle positions favour rapid direct suppression while higher positions favour general area cooling but take substantially longer to extinguish a fire unless compensated by higher pressure, higher flow rate or faster (smoke-based) detection. However, no single study varies both nozzle height and fuel type together under otherwise identical conditions, which is identified as the principal research gap motivating the experimental programme proposed in this work.

Keywords: Water mist; Nozzle discharge height; Fire suppression; Extinguishment time; Fire dynamics; Droplet momentum; Fire protection