Fired-Heater Light-Off Firebox Explosion

Before lighting a fired heater, furnace, or boiler, the firebox must be purged to sweep out leaked fuel. Light off without a proper purge — or keep feeding fuel to a burner that failed to light — and the accumulated fuel-air mixture explodes on the ignition attempt.

Firebox explosions on light-off are the canonical burner-management failure; NFPA 86 and API burner-management standards exist almost entirely to force the purge-verify-light sequence this card trains.

1. Complete the measured pre-ignition purge (duration/volumes per NFPA 86 / BMS permissives) before any light-off.
2. Verify fuel valves are tight (no leak-by loading the box during the purge).
3. Light each burner per sequence and confirm flame on each before proceeding.
4. On any failure-to-light, isolate fuel immediately.
5. Re-purge fully before every re-attempt — never ignite into an unpurged or fuel-rich box.

Scenario-specific frequency: not quantified in public sources; published root-cause reports on furnace explosions repeatedly come back to inadequate pre-purge, bypassed BMS interlocks, and undetected flame failure ( industry-literature pattern, e.g. [National…

Class-level: firebox explosions kill and injure operators at the heater and destroy the fired equipment; the extreme fuel-reaches-firebox case is Skikda 2004 (27 dead — see card_02_08). Majority of serious boiler-related accidents involve fatalities per…