Buncefield bosses were overworked and badly trained

Court hears workers at oil depot were under pressure to fill tanks to capacity

Workers at Buncefield oil depot were under pressure to fill tanks to their maximum in the months before an "almighty" explosion ripped through the site, a court heard yesterday.

Supervisors at the depot were also overworked and did not receive the training they needed, while the device used to measure the levels of the tanks was inaccurate, the court was told.

St Albans Crown Court heard that the explosion at the depot near Hemel Hempstead, Hertfordshire, on 11 December 2005, happened after vapour from 250,000 litres of petrol started to spill out from the top of one of the tanks at the depot. The environmental damage of the explosion is still not known but could last for decades, the court heard, as three companies went on trial accused of health and safety breaches.

Hertfordshire Oil Storage Ltd (HOSL), TAV Engineering Ltd and Motherwell Control Systems 2003 Ltd are being prosecuted by the Health and Safety Executive and the Environment Agency. It is alleged that HOSL "manifestly failed" in its duty to ensure the site was safe.

Under an historical agreement, a "commercial fine" had to be paid to the British Pipeline Agency if the depot didn't take a certain amount of fuel from two of the three lines that came in from refineries, the court heard.

To add to the pressure facing the depot, supervisor Steven Lewis was trying to bring in a new management system to run the site after it was transferred from Fina to Total, while gauges made by Motherwell Control Systems 2003 Ltd used to measure the fuel levels in the tanks often became stuck.

Andrew Langdon QC, prosecuting, said: "Supervisors didn't get much help or protection in what they did. They didn't get any risk assessments worth their name – pretty essential you might think – how the tanks should be filled, how they should be emptied, what happens with all these considerations."

Turning to the jury, the barrister added: "You might be thinking that if you had a supervisor's job you wouldn't fill the tanks to the high level. It is surely less stressful to fill them to a lower level but there was a pressure. The sheer volume that came through this terminal had increased over the years, it may have increased three or four-fold over a decade."

The court heard that petrol stored in one tank could fill 100,000 cars while, in 2005, an estimated 400 tankers visited the depot every 24 hours. The site was often busiest between 4am and 6am.

The jury was also told that shortly before 6am on the day of the explosion, vapour from 250,000 litres of petrol spilled from the top of a storage tank at the depot. Shortly after 6am it ignited causing an "almighty" explosion, similar to an "earthquake". In written evidence read to the court, tanker driver Paul Reed, who witnessed the blast, said: "All of a sudden I felt a whoosh coming from behind me. It was like a strong wind thudding me in the back. Immediately following the whoosh was a massive and loud explosion. The force of this blew me off my feet and on to the floor."

Total UK has already admitted three health and safety breaches while the British Pipeline Agency Ltd has admitted two charges. Motherwell Control Systems 2003 Ltd is in voluntary liquidation. The case continues.

Timeline: Oil disaster

11 December 2005 Explosions rip apart Buncefield oil depot and start a fire which takes five days to put out.

12 January 2006 Lord Newton of Braintree is appointed to chair inquiry.

9 May 2006 Report identifies how vapour cloud formed from overflowing Tank 912 and ignited.

29 March 2007 Board makes 25 safety recommendations.

17 July 2007 HSE calls for industry-wide safety improvements.

1 December 2008 It is announced that five companies will be prosecuted.

11 December 2008 Final report estimates total cost of fire at £894m and makes 78 recommendations.

20 March 2009 High Court rules Total is liable for £750m in damages.

15 April 2010 Trial of three firm on health and safety charges begins. A fourth has admitted two charges.