In the early hours of Sunday 11 December 2005, the Buncefield oil storage depot in Hemel Hempstead, UK, was rocked by a massive explosion.
The blast was caused by a vapour cloud explosion (VCE) - when a cloud of flammable vapour, gas, or mist ignites, creating a sudden and powerful overpressure.
One of the initial explosions registered 2.4 on the Richter scale, sparking a huge fire that engulfed most of the site.
Around 2,000 people were evacuated, over 40 were injured, and nearby homes and businesses suffered major damage.
The fire burned for several days, sending thick black smoke across southern England and disrupting fuel supplies to London and the Southeast.
The Buncefield disaster started when Tank 912 overfilled because its critical safety equipment didn’t work.
The tank’s automatic gauge and independent high-level switch failed, and the valves that should have stopped the overflow didn’t operate.
Fuel spilled out, forming a dense vapour cloud that spread across the site and into nearby areas.
At 06:01, the first explosion spread through the depot, followed by more blasts and a fire that consumed over 20 tanks.
The incident investigations showed that problems weren’t just in the tank’s primary containment itself.
The disaster highlighted weaknesses in all three levels of containment:
- Primary containment – the tank and pipework holding the fuel - failed
- Secondary containment, such as high-level alarms and bunds designed to catch spills, was overwhelmed
- Tertiary containment, including drainage, kerbs and surface features meant to slow or hold escaping liquids, also failed.
Buncefield presented a clear message to high-hazard industries: storing flammable liquids safely requires a robust, well-maintained three-layer containment system.
