Question 67 QMED04 - Boiler Technician-Watertender

The Correct Answer is A ### Explanation for Option A (CO2) **CO2 (Carbon Dioxide)** extinguishers are the preferred choice for fires in sensitive electrical equipment, such as an automation console (a Class C fire), once the power has been secured. 1. **Non-Conductive:** CO2 is an inert gas that does not conduct electricity, making it safe to use around high-voltage equipment, even if residual charge is present. 2. **No Residue:** CO2 works by displacing oxygen (smothering the fire) and cooling the area. Crucially, it leaves absolutely no damaging residue behind. This ensures the survival of adjacent sensitive electronics within the console after the fire is extinguished. ### Explanation of Incorrect Options **B) Foam:** Foam extinguishers are water-based and highly conductive. They are primarily used for Class A (ordinary combustibles) and Class B (flammable liquids) fires. Using foam on electrical equipment (even if the main power is secured) poses a severe electrical hazard and would permanently ruin the sensitive components within the console. **C) Soda acid:** Soda acid extinguishers are obsolete and primarily used for Class A fires. They contain a corrosive, water-based solution that is highly conductive and extremely damaging to electrical equipment. They are entirely unsuitable for Class C fires. **D) Dry chemical:** Dry chemical extinguishers (such as ABC powder) are effective at putting out Class C fires because the agent is non-conductive. However, the powder (usually monoammonium phosphate or sodium bicarbonate) leaves a heavy, corrosive, and difficult-to-clean residue. While effective at extinguishing the fire, this residue will likely destroy the sensitive circuit boards and components inside the console, making CO2 the significantly superior choice for minimizing equipment damage.