Question 53 QMED03 - Oiler

The Correct Answer is D **Explanation for Option D (Correct):** Option D describes the mandatory safety procedure that must be followed after a failed light-off attempt on an idle boiler. When a light-off fails, it means that unburned fuel (gas or oil vapor) has entered the furnace. This unburned fuel accumulates and creates a highly volatile, potentially explosive mixture within the confined space of the furnace and gas passages. To prevent a furnace explosion (or "blowback") upon the next ignition attempt, all fuel must be immediately secured (shut off) to stop the flow of more combustibles. Following this, the furnace must be thoroughly purged using the forced draft (FD) fan to flush out all accumulated explosive vapors and introduce fresh air. Only after a sufficient purge cycle (which is specified by regulatory codes and manufacturer recommendations, often 4 to 8 air changes) is it safe to attempt re-ignition. **Why Other Options Are Incorrect:** * **A) The fuel should be secured to the boiler and the boiler allowed to remain idle for a few minutes before another light-off attempt is made.** * This is incorrect because it secures the fuel but fails to address the critical safety hazard: the existing accumulation of combustible vapors in the furnace. Simply waiting a few minutes without purging the furnace leaves the explosive mixture intact, making the next light-off attempt extremely dangerous. * **B) Another light-off attempt (just one) can be undertaken before any additional precautions need to be observed.** * This is highly dangerous and violates standard safety procedures. Attempting to light the boiler again without first purging the furnace guarantees that the ignition source will encounter the rich, explosive fuel-air mixture that caused the first failure, almost certainly resulting in a furnace explosion. * **C) Another light-off attempt (with no limit) can be undertaken before any additional precautions need to be observed.** * This is fundamentally and catastrophically unsafe. Repeatedly attempting ignition without purging is an invitation to a major industrial accident (furnace explosion) and is prohibited by all standard boiler operating codes.