How is the numerical rating decided for Class K portable fire extinguishers?

Class K portable fire extinguishers, which are specifically designed for kitchen fires involving cooking oils and fats, do not have a numerical rating assigned to them. This is because the nature of the hazards they address is unique compared to other classes of fire extinguishers, such as those intended for electrical or combustible solid fires.

Unlike other classifications where a numerical rating can indicate the effectiveness based on the type and size of the fire, Class K extinguishers are evaluated based on their ability to effectively suppress grease fires without a standardized numerical scale. They are tested under specific conditions that demonstrate their efficacy in real-world scenarios of cooking fires, focusing heavily on the extinguishing agent’s performance in those environments.

In contrast, the other potential answers suggest scenarios where ratings could be mathematically derived or based on user testing with defined parameters. However, such methods do not apply to Class K extinguishers, reaffirming the unique nature of their classification.