Basic safety-management failings were the root cause of Britain’s most costly industrial disaster, according to a new report published on 16 February.

In July 2010, five companies were fined a total of £9.5million for their part in causing the explosion and five-day fire at the Buncefield Oil Storage Depot, which resulted in massive environmental damage and devastated the local community.

The full story of the joint investigation by the HSE and Environment Agency into the 2005 disaster is told for the first time in the report, The Buncefield explosion: Why did it happen?

Drawing on previously unpublished material, held back until the criminal prosecution was completed and the appeals processes had run their course, the 36-page report identifies several contributory factors to the disaster. Not least, it condemns the development of a culture where maintaining operations was seen as more important than safe processes, which did not get the attention, resources, or priority status they required.

Part of the report found that an automatic gauging system that was fitted to a tank and set up to measure the rising level of fuel flatlined. As a consequence, three alarms that were meant to sound if the level of fuel exceeded the tank’s capacity did not operate and, due to the practice of working to alarms in the control room, the control room supervisor was not alerted to the fact that the tank was dangerously full.

An independent high-level switch (IHLS) set at a higher level than the alarms was intended to stop the filling process by automatically closing valves on any pipelines, as well as sounding an audible alarm should the petrol in the tank reach an unintended high level.

However, the IHLS also failed to register the rising level of petrol, so the final alarm did not sound and the automatic shutdown was not activated. Just before 6 am, 11 December, the level within the tank exceeded its ultimate capacity and petrol started to spill out of vents in the tank roof, the report said.

Gordon MacDonald, chair of the COMAH Competent Authority Strategic Management Group, which published the report, said: “Major industrial incidents are, thankfully, rare – this report will help make them even less frequent by sharing some key insights and lessons with the wider high-hazard industries.

“Companies that work in a high-hazardous industry need to have strong safety systems in place, underpinned by the right safety culture. Buncefield is a stark reminder of the potential result of a poor attitude towards safety.”

With estimated total costs exceeding £1billion, the Buncefield explosion remains Britain’s most costly industrial disaster. For the full news story, check out sister site SHP's coverage.

The report, The Buncefield explosion: Why did it happen? is available online.