Question 35 QMED03 - Oiler

The Correct Answer is B **Explanation for Option B (Correct):** The primary purpose of purging a boiler furnace prior to ignition is safety. During periods when the boiler is idle or shut down, small leaks of fuel (combustible vapors, such as natural gas or atomized fuel oil residue) can accumulate in the furnace. If ignition is attempted while these vapors are present, a rapid, uncontrolled combustion event known as "flareback" or "furnace explosion" can occur. Therefore, the furnace **must first be purged of combustible vapors**. This is achieved by introducing a large volume of air, usually from the **forced draft blower**, to sweep out these flammable gases. To ensure the air flow effectively sweeps through the furnace and exits the stack, the **air register doors must be open** to allow maximum air input and proper distribution. **Explanation of Incorrect Options:** * **A) The furnace must first be purged of inert vapors and oxygen with the forced draft blower while the air register doors are open.** * This is incorrect because the goal is not to purge *inert vapors* (which are non-flammable and harmless in this context) or to purge *oxygen*. Oxygen is necessary for combustion, and attempting to purge it would make ignition impossible. The critical hazard to remove is the **combustible vapors**. * **C) The furnace must first be purged of combustible vapors with the forced draft blower while the air register doors are closed.** * This is incorrect because closing the air register doors severely restricts the amount of air that can enter the furnace and limits the flow path, making the forced draft purge ineffective. A proper purge requires maximum airflow, meaning the air registers must be **open**. * **D) The furnace must first be purged of inert vapors and oxygen with the forced draft blower while the air register doors are closed.** * This is doubly incorrect. As explained for Option A, the goal is not to purge inert vapors or oxygen. As explained for Option C, the air register doors must be **open** for an effective purge.