An experimental study of the effects of water mist characteristics on pool fire suppression

Suppression of pool fire by a water mist is influenced by mist characteristics, its location and orientation relative to the fire. A heptane pool fire was generated in 1 m × 1 m × 1 m chamber in a 125 mm diameter pan. Mist was generated with a pair of twin-fluid atomizers installed at the ceiling centre. Nitrogen at 4–8 bar and 104–136 LPM flow rate aspirated water at 0.18–0.22 LPM. Mean droplet diameter and velocity measured at 500 mm and 850 mm from the atomizer were 18–30 μm and 2.2–3.2 m/s, respectively. The fire was produced at four locations and mist was activated 30 s after fire initiation. Temperatures were measured along the flame centreline at 160, 360 and 560 mm above the fuel surface. CO, CO2 and O2 concentrations were also measured. Mean droplet diameter decreased and velocity increased with increasing nitrogen pressure. Fire suppression time decreased with increasing gas pressure approaching asymptotic value for pressures greater than 6 bar for all location of fire. The fastest suppression (12–18 s) was achieved for fire at the chamber centre where mist spray was symmetrical and slowest (47–68 s) for farthest location of fire from mist.

► Fire produced in a 125 mm diameter pan (6.5 kW) in a 1 m3 chamber at 4 locations.
► Twin fluid atomizer operated with N2 at 4–8 bar, generating mist at 180–220 mLPM and Dv50 ∼ 18–30 μm.
► Flame centre-line temperatures, CO, CO2 and O2 concentrations measured for non-penetrating mist.
► Suppression times 13–68 s, decreases with increasing pressure up to 7 bar.
► Suppression time is greatest (68–19 s for 4–8 bar) at the farthest fire location.