Cooking oil fires, compared to other types of liquid fuel fires, are difficult to extinguish, because they burn at high temperature and re-ignite easily. During the 2 min of free burn, the cooking oil fire was fully developed and the oil was further heated to a higher temperature. The highest oil temperature measured in the tests was 403oC, which was 38oC above the auto-ignition temperature. Also, the change in oil composition during the free burn and fire suppression periods reduced the auto-ignition temperature of the oil below its original auto-ignition temperature. The lowest auto-re-ignition temperature measured in the experiments was approximately 65oC below the original auto-ignition temperature.
Full-scale fire experiments demonstrated that the water mist fire suppression systems developed in the present work were capable of extinguishing cooking oil fires and preventing their re-ignition. The predominant extinguishing mechanism was the cooling of the fire plume and the wetting/cooling of the oil. Extinguishing cooking oil fires requires flame extinction over the entire surface at once and rapid cooling of oil below its auto-re-ignition temperature to prevent re-ignition. The fullscale testing results indicated that spray momentum, spray coverage area and flow rate are the three most important factors that determine the effectiveness of a water mist system for extinguishing cooking oil fires. The discharge of water mist does not cause oil to splash outside the fryer.