Smoke stack: The explosion at Buncefield in 2005 was the largest in Europe since the end of the Second World War
The explosions that rocked the Hertfordshire oil storage terminal in December 2005 were reckoned to be the largest ever in peacetime Europe. They could be heard as far away as Belgium, France and the Netherlands.
A fuel-air explosion and fire set off a string of other explosions at the terminal – which was the fifth largest oil products facility in Britain at the time, owned by Texaco and Total.
The inquest into the accident plumed outwards like smoke from the fire, which had reached the English Channel by the time the blaze was extinguished two days after the explosions. It emerged that one storage facility had reignited in the process and been left to burn. In all, 20 tanks had been overwhelmed.
How such a destructive event had happened was not readily understood. A terrorist attack was hypothesised in the days following the blast, along with more prosaic theories about the failure of fuel leak detection equipment at ground level.
A year on from the incident, the Buncefield Major Investigation Board declared that the explosion had been so violent and had “generated such extreme over-pressures” that it would take “many years” to understand.
Investigators focused on establishing practical steps to ensure that escaping fuel would not cause such a catastrophe in future. The need was for safety measures to prevent fuel escaping from tanks in the first place – and that stopped it forming into a vapour when it did.
One company working on the causes of the disaster was Norway’s GexCon, which provides consultancy services in safety and risk management and, in this case, computer-aided modelling of explosions and fires. The firm has detailed knowledge of explosion phenomena built up through years of extensive research projects and accident investigations, including performing physical testing at the company’s facilities on the island of Sotra, outside Bergen.
The firm’s expertise was drafted in by the Buncefield investigators to help ascertain what had happened during the disaster. It wasn’t the first big accident inquiry that the company had worked on: it also helped to investigate the Piper Alpha oil rig fire of 1988, which killed 167 workers, and the crash of TWA flight 800 – a Boeing 747-100 that exploded over the Atlantic Ocean near New York in July 1996.
GexCon was also involved in investigating the Petrobras P-36 disaster in 2001, in which explosions led to the sinking of a semi-submersible oil rig off the Brazilian coast. Eleven people were killed.
Dr Prankul Middha, general manager for consulting at GexCon, has been with the firm since 2005. He says the company, which is owned by a not-for-profit Norwegian research institute, uses modelling technology similar to computational fluid dynamics software. The firm can act as an ‘expert witness’ when an accident is being investigated.
“In the UK, it is our work on Buncefield that is fresh in people’s minds,” he says. Total contracted GexCon to produce its own reconstruction of the accident. Middha adds: “The main issue with Buncefield was, when it happened, people did not understand why. They thought that if an incident did happen it would have relatively minor consequences. Here, 15 miles away, windows were broken. It was a very strong explosion.”
GexCon began by carrying out surveys of the site which revealed dense lines of trees around two sides of it – an environmental feature that was later found to have contributed to the scale of the blast. Explosions increase in scale when they hit obstacles, Middha explains. He says: “For instance, a fuel can burn and travel at one or two metres a second, but put all these obstacles in the way and it could accelerate to a few hundred metres a second.”
He adds: “At detonation level, it is moving at a couple of kilometres a second and up to 20 times the atmospheric pressure. We thought these tree lines were sufficient to cause that.” The Hertfordshire oil storage terminal site and the tree lines were modelled by GexCon. This work was used by the Health and Safety Executive, whose Buncefield Standards Task Group drew up a report detailing the measures oil companies should take to ensure that such an incident never recurred. The research was also drawn on by the industry-backed Fire and Blast Information Group, which disseminates best-practice advice to help design against the possibility of hydrocarbon fires and explosions.
Life-saving: GexCon can suggest the best place to locate living quarters away from potential accidents
As well as acting as a consultant following explosions, GexCon markets its software around the world and has more than 150 users, including oil majors, chemicals firms and safety consultancies. If GexCon is acting in a consultancy role itself in the wake of a fire or explosion, it will model a reconstruction of the site.
“The starting point for that is a site survey, and getting a picture of the damage,” says Middha. “We can construct a computer model of this based on layouts from the owner or site manager. Let’s say it was a gas leak – we can model it igniting, and reproduce the damage. And then we can come up with theories concerning why it happened.”
Physical testing is also an important weapon in the company’s armoury. It is expanding its test facilities on the island of Sotra, west of Bergen, Norway. A new test site will be built, eight times larger than the current one, to include extended testing facilities and infrastructure, and state-of-the-art measurement equipment.
The island test site already carries out gas, oil mist and dust explosions in addition to jet fire, pool fire and compartment fires. New indoor facilities will be added for mechanical work and for winter testing. Further services will include large-scale gas explosion and dispersion tests, course activities and live demonstrations.
Aspects of a design that GexCon can test include safety-critical equipment such as rupture discs or relief panels, which are designed to relieve pressure in the event of a fire. The company can also certify that equipment is not an effective ignition source under the European Union Atex directive. The developments on Sotra are set to be complete by the autumn, said the company.
If an offshore rig is being designed, GexCon can help with the layout of the living quarters, to insulate them as far as possible from the potential effects of an accident. “Most oil and gas companies would use us as external consultants for large projects,” says Middha.
“Your goal with the software is to be predictive. You have a model of your facility, and you have a model of your incident.”
After incidents such as Piper Alpha, he says, the industry knew it needed to adhere to the strictest safety standards, continuously improving them over time.
“We understand the physics underlying explosions, and can then optimise the layout of industrial plant for safety,” Middha concludes.
In the dock
In April 2010 the five companies accused of causing the Buncefield explosion faced a criminal prosecution brought by the Health and Safety Executive and the Environment Agency. Two defendants, Total’s UK division and the British Pipeline Agency, had already pleaded guilty to offences under the Health and Safety at Work Act.
The remaining three, Hertfordshire Oil Storage, TAV Engineering and Motherwell Control Systems, were found guilty in June 2010.
TAV and Motherwell Control Systems were convicted of failing to protect employees. Hertfordshire Oil Storage was found guilty of failing to prevent major accidents and limit their effects – and then pleaded guilty to causing pollution to enter controlled waters in the vicinity, contrary to the Water Resources Act.
Sentencing took place the following month, with Total UK the biggest loser: it was fined £3.6 million plus £2.6 million costs. Hertfordshire Oil Storage was fined £1.45 million and £1 million in costs.
The two engineering firms involved, Motherwell Control Systems and TAV, were fined a modest £1,000 each.