Effect of foam air mixing on flame intensification -- comparative experimental study of foam and water sprays extinguishing transformer oil pool fire.

In this paper, the mechanism of flame intensification during the suppression of transformer oil pool fire is investigated for foam and water sprays. The results show that the extinguishment time is proportional to the discharge height and inversely proportional to the discharge pressure because greater height or lower pressure reduces the amount of suppression agent reaching the fuel bed thus extending extinguishment time. The increase of heat release rate following activation is inversely proportional to the discharge height and directly proportional to the discharge pressure; again, affected by the amount of suppression agent. When the nozzle is above the flame, the foam spray is affected by the entrapped air within, resulting in greater flame intensification, which is 3.5 times compared to water spray. For radiation, when the nozzle is above the flame, the heat flux increase is inversely proportional to the discharge pressure, which differs from the relationship for heat release rate increase. This difference is due to the shielding effect of the blanketing spray. For predict the heat release rate increase, an empirical model is developed, and an air mixing coefficient, τ, is introduced for foam spray to account for a 20%–35% increase in the heat release rate. [ABSTRACT FROM AUTHOR]