Question 68 QMED01 - Junior Engineer

The Correct Answer is A. **Explanation for Option A (Correct):** Option A is correct because before attempting to ignite a burner in a cold or idle boiler, the primary safety procedure is to perform a **furnace purge**. A purge is necessary to remove any accumulation of unburnt fuel, combustible gases (like methane or residual fuel vapors), or volatile mixtures that may have leaked into the furnace or boiler passes while the unit was idle. If ignition is attempted with a concentration of combustible vapors present, the mixture could ignite explosively, causing a dangerous condition known as **boiler flareback** (or furnace explosion). The purge must be executed using the **forced draft (FD) blower** to move a sufficient volume of air through the furnace. The **air register doors must be open** during the purge to ensure maximum airflow and complete ventilation of the furnace space and combustion pathways, effectively sweeping out the combustible vapors. **Explanation of Incorrect Options:** * **B) 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 of the pre-light-off purge is to remove *combustible vapors*, not "inert vapors and oxygen." Oxygen is necessary for combustion and is deliberately supplied by the FD blower during the purge. * **C) 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 incorrect for two reasons: (1) The goal is to remove combustible vapors, not inert vapors and oxygen (see B). (2) The air register doors must be **open** during the purge to allow the air from the FD blower to fully ventilate the furnace. Closed registers would prevent effective purging. * **D) 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 although the goal is correctly identified as removing "combustible vapors," the safety requirement is that the air register doors must be **open** during the purge. Closed registers would throttle airflow and prevent the complete removal of the volatile mixture, rendering the purge ineffective and maintaining the risk of flareback.