Buncefield explosion: 20 years on

The Buncefield oil depot explosion still feels like a wake-up call for anyone dealing with bulk storage and management of highly flammable liquids and major incident planning.

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.

What went wrong

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.

Secondary and tertiary containment measures also failed to stop the fuel spreading, highlighting how quickly things can escalate when safety layers break down.

Primary containment, like the tank itself, failed. Secondary containment, including bunds meant to catch spills, was overwhelmed.

Even tertiary containment, such as drainage and surface barriers, couldn’t stop the spread. Each layer matters, and when they all fail, the results can be catastrophic.

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.

Twenty years on, Buncefield still sends a clear message to high-hazard industries: storing flammable liquids safely requires a robust, well-maintained three-layer containment system.

Lessons learned

The Buncefield explosion taught the global operators of bulk fuel storage tanks some invaluable lessons. One major takeaway was the potential failure of the bunds - the walls meant to contain fuel.

At the time of the incident, they couldn’t cope with the volume of fuel mixed with firewater and firefighting foam, which found multiple ways to escape into the environment, and causing environmental pollution.

For anyone running a fuel storage site, this is a clear signal: check your containment systems, know where overflow might go, and consider increasing bund capacity.

The incident also highlighted the importance of planning for the worst-case scenario. Even the best emergency plans can fall short if they underestimate the scale of an incident. 

Regular drills and clear communication lines between site operators, local authorities, and emergency services are essential.

Buncefield showed that coordination saves lives and limits damage, but preparation must be realistic and robust.

Finally, equipment and materials matter. Bunds need to withstand fire conditions, and firefighting foam should meet the latest environmental standards. Training staff and designing sites with extreme events in mind are essential.

The lessons from Buncefield are global: the unforeseen will happen, and the better prepared we are, the safer our communities will be.

Reference

Final report of the Major Incident Investigation Board Incident – Volume 2 (PDF 4.3MB).