What is the primary advantage of a wet chemical extinguishing system over a dry chemical system when used for Class K cooking oil fires?

The primary advantage of a wet chemical extinguishing system over a dry chemical system when used for Class K cooking oil fires is its unique ability to prevent reflash by simultaneously cooling the superheated oil and creating a lasting, non-combustible vapor-sealing blanket. Class K fires involve combustible cooking oils and fats, which burn at extremely high temperatures. Dry chemical systems extinguish fires primarily by interrupting the chemical chain reaction of the flames and by creating a temporary smothering effect. While a dry chemical agent can initially put out the visible flames of a Class K fire, it does not significantly cool the superheated cooking oil. Because the oil remains well above its autoignition temperature, the fire can easily re-ignite once the dry chemical powder disperses and oxygen becomes available again, a phenomenon known as reflash. In contrast, wet chemical systems are specifically formulated for Class K fires. Their extinguishing agent is an alkaline solution, typically containing potassium acetate, potassium carbonate, or potassium citrate. When this wet chemical agent is applied to hot cooking oil, two critical processes occur: first, a chemical reaction called saponification transforms the burning oil or fat into a non-combustible, soapy foam-like substance; second, the water content within the wet chemical agent rapidly cools the superheated oil below its autoignition temperature. The combination of saponification and cooling creates a durable, non-combustible blanket, or vapor seal, over the surface of the cooking oil. This vapor seal effectively smothers the fire by preventing oxygen from reaching the fuel and, critically, suppresses the release of flammable vapors from the hot oil. This dual action of cooling the fuel and establishing a stable vapor seal is what definitively prevents reflash, ensuring the fire remains extinguished.