Storage-Tank Overfill (High-Level)

A tank is being filled while its level gauge stops updating and the independent high-level cutoff isn't working. The tank overflows, a large flammable vapor cloud forms at ground level, and finds ignition.

Buncefield (11 December 2005): tank 912 overfilled ~300 tonnes of gasoline; the gauge had stuck (a known intermittent fault) and the independent high-level switch was inoperable because a required padlock was never fitted. The vapor cloud exploded — one of Europe's largest peacetime explosions (Buncefield MIIB report).

1. Confirm the high-level trip is functional BEFORE starting the transfer.
2. Cross-check level by independent means during filling (volume balance, timing, manual gauging).
3. Treat a non-moving gauge during an active fill as failed, not fine.
4. Stop the transfer at the first unresolvable discrepancy.

Insurance-industry data: overfills occur about once per 3,300 tank fillings — the statistic behind API 2350's overfill-prevention requirements (Emerson, The Complete Guide to API 2350,…

Overflow, ground-level vapor cloud (~360 m diameter at Buncefield before igniting ~22 minutes after first CCTV sighting), explosion and multi-tank fire; Buncefield injured 43 and destroyed the terminal (Buncefield MIIB).