Question 55 QMED05 - Machinist-Pump Technician

The Correct Answer is A. Aqueous Film Forming Foam (AFFF) is a highly effective fire-extinguishing agent primarily designed for Class B (flammable liquids) fires. It works by creating an aqueous film that floats on top of the liquid fuel, sealing the surface, blocking oxygen access, and suppressing the release of flammable vapors. Engine room bilges often accumulate spilled oils and fuels, leading to potential **oil fires (Class B)**. AFFF is especially suitable here because its density allows it to float on and cover hydrocarbon fuels, and its "light water" nature helps it flow and spread rapidly across the surface area typical of a bilge fire, quickly knocking down the flames. Here is why the other options are incorrect: **B) any class D fire:** Class D fires involve combustible metals (like magnesium, titanium, or potassium). AFFF (which contains water) is generally unsuitable and potentially dangerous for most Class D fires, as water can react violently with these metals, intensifying the fire. Specialized dry powder agents are required for Class D fires. **C) class C fires in paint lockers:** Class C fires involve energized electrical equipment. While AFFF is a versatile foam, standard AFFF is conductive and should not be used on energized electrical fires (Class C), especially in confined spaces like paint lockers (which often contain electrical fixtures). Furthermore, paint lockers typically involve solid combustibles (Class A) and flammable liquids (Class B). While AFFF can handle the Class B component, CO2 or dry chemical agents are often preferred for Class C fires, and water or standard foam for Class A. **D) all of the above:** Since AFFF is incorrect for Class D and inappropriate for standard Class C (electrical) fires, this option is incorrect.