Question 8 QMED04 - Boiler Technician-Watertender

The Correct Answer is B **Explanation of Option B (Correct):** Dry chemical extinguishing agents (such as sodium bicarbonate, potassium bicarbonate, or monoammonium phosphate) are solids that are finely powdered. A major advantage of these substances is their **good stability** (meaning they have a long shelf life, remain effective, and do not readily decompose under normal storage conditions) and their **non-toxicity** (they are generally safe for humans, though inhalation of the powder should be avoided, and they are safe for the environment in comparison to some other agents). They achieve extinguishment primarily through chemical interference with the combustion chain reaction. **Explanation of Incorrect Options:** * **A) permanent extinguishment regardless of the reignition sources:** This is incorrect. Dry chemicals are highly effective at suppressing flames, but they provide **no significant cooling or inerting effect** (unlike water or CO2). If the heat source (reignition source) is still present, the fire can immediately reignite after the discharge stops. They do not ensure "permanent extinguishment" in the absence of control over the ignition source. * **C) its excellent cooling ability:** This is incorrect. Dry chemical agents have **poor cooling ability**. Their primary extinguishing mechanism is chemical inhibition (breaking the combustion chain reaction), not cooling. Water and specialized cooling foams are used when excellent cooling is required. * **D) all of the above:** Since options A and C are incorrect, this option is also incorrect.