Which form of foam is least effective on water-insoluble liquids?

Alcohol-resistant foam is specifically formulated to combat fire hazards associated with water-miscible substances, which are liquids that can mix with water, making these environments more challenging to manage. Water-insoluble liquids, such as oils and various hydrocarbons, do not mix with water and present a different problem for firefighters.

The effectiveness of foam types is tied closely to their intended purpose. Aqueous Film-Forming Foam (AFFF) and Class B foam are specifically designed to combat flammable liquids, forming a barrier that smothers the flames while also cooling the surface. High expansion foam can also be effective for certain applications, but it varies with the specific type of application and the characteristics of the burning material.

In contrast, alcohol-resistant foam is tailored for situations involving water-miscible solvents, making it less compatible and effective when fighting fires involving water-insoluble liquids. Therefore, among the options listed, alcohol-resistant foam is least effective on water-insoluble liquids, while the other foam types are geared more towards tackling such fires effectively.