Why should water not be used on a Class K cooking oil fire?

• A. Water can be used safely and effectively
• B. Water is more effective than the wet chemical
• C. Water can cause violent splashing and spreading of burning oil and is ineffective against fats
• D. Water cools too slowly

Answer: (C)

Water should not be used on a Class K cooking oil fire because oil and water do not mix and have very different densities. When water is poured onto hot oil, the water sinks to the bottom and instantly turns to steam. That rapid expansion pushes burning oil and droplets out of the pan, causing a violent flare-up and spreading the fire. Water also doesn’t mix with oil to cool it effectively, so the fat keeps burning even as steam erupts.

The safe, effective approach is to use a wet chemical Class K extinguisher or to smother the fire with a lid or other appropriate method to deprive the flames of oxygen and allow the oil to cool. The wet chemical agent chemically reacts with fats to form a soapy layer that helps cool and seal the surface, preventing re-ignition.