When should a wet chemical extinguisher not be used on Class K fires?

A wet chemical extinguisher is specifically designed for Class K fires, which involve cooking oils and fats. However, its use prior to the activation of a fixed extinguishing system, such as a kitchen hood suppression system, may not be advisable. This is because the wet chemical is intended to cool and smother the flames, but if a fixed system is already in place and has not activated, using the extinguisher prematurely could disrupt the intended operation of that system and potentially compromise safety.

In situations where the fixed system operates effectively, it is often best to allow it to handle the fire, especially in larger-scale incidents. The fixed systems are designed to deal with these types of fires, often more effectively than a portable extinguisher can, particularly if there is a considerable amount of fire present. Thus, while the wet chemical extinguisher is effective in many scenarios involving Class K fires, using it before the activation of a fixed system could lead to inefficiency in firefighting response.