OHST Practice Exam

Which firefighting agent is effective on a Class A fire?

1. Purple K

2. Halon 1301

3. Dry Chemical (Potassium Chloride)

4. Dry Chemical (Ammonium Phosphate)

The correct answer is: Dry Chemical (Ammonium Phosphate)

Class A fires involve ordinary combustible materials such as wood, paper, and textiles. The correct firefighting agent effective for extinguishing Class A fires is the dry chemical agent, specifically ammonium phosphate. This agent works primarily by cooling the burning material and forming a barrier between the material and the oxygen in the air, which is essential for combustion. Ammonium phosphate not only smothers the fire but also absorbs heat, making it highly effective for this type of fire. Other agents mentioned are less effective or suitable for Class A fires. For instance, Purple K is primarily designed for Class B and C fires—those involving flammable liquids and gases—and may not be efficient on Class A fires. Halon 1301 is a clean agent used typically for protecting electronics and class B and C fires, but it does not effectively deal with solid combustibles. Potassium chloride, another dry chemical, is more specialized for Class B fires, often used in extinguishers for flammable liquids and gases. Therefore, ammonium phosphate stands out as the best option for addressing Class A fires.