The UK Petroleum Industry Association (UKPIA) yesterday described the explosion at the Buncefield plant near Hemel Hempstead as a one-off and said the industry's safety record was better than its peers.

But the oil and gas sector might have been lucky until now. Less than two weeks ago the Health & Safety Executive (HSE) damned ConocoPhillips for "potentially catastrophic" lapses that caused a fire and explosion at its Humberside refinery.

And the US Department of Labor has just referred an investigation to state justice officials, which may lead to a criminal prosecution against BP for an explosion at its Texas City refinery earlier this year.

Safety procedures were tightened up in the North Sea after the Piper Alpha disaster in 1988, in which 167 people died. However, over the last 18 months there has been a series of offshore gas leaks that could have had fatal consequences.

Total, the operator of the Buncefield petrol and diesel distribution plant, said yesterday that it was too early to say what went wrong at the Hertfordshire site and the UKPIA said no one should try to apportion blame at this stage.

Nick Vandervell, the industry body's spokesman, said an incident of this kind "had never happened before" and the industry had put in place "closed loop" systems to avoid dangerous vapour escapes. The oil and petroleum sector was, by its very nature, dangerous, in that companies are dealing with highly inflammable substances, added Mr Vandervell, but firms worked closely with the HSE.

"The safety record of the UK refining and distribution industry business is better than the other industrial sectors and the wider European industry," he argued.

Mr Vanderwell pointed to latest statistics covering 2003 showing that there were fewer than 50 reported incidents involving any kind of injuries and argued that "an awful lot of money" had been spent upgrading systems.

Yesterday Total and other oil companies worked to ensure that there were no fuel shortages, despite the country's fifth largest distribution complex being out of action.

But the report by the HSE into the accident at Conoco's Humberside plant on April 16 2001, paints a picture of a different kind of industry. "Our investigation revealed that as well as failing to inspect pipework at its site adequately, the company's management had not correctly analysed the effects of an operating change, nor recorded it. This led to operators, inspection and monitoring staff not having a common understanding of the actual operating arrangements at the plant," it concluded in a little publicised report issued on 1 December.

Six months ago the US oil group was fined over £1m, at Grimsby crown court for breaches of health and safety legislation in relation to the fire. Conoco was unavilable for comment last night.

The HSE described the incident as "very serious and had the potential to be catastrophic" while safety authorities earlier this year warned North Sea companies that the number of fatal and major accidents was "unacceptably high".

Workers have been evacuated from a series of platforms such as Marathon's Brae field one and Shell's Cormorant and Dunlin platforms after gas leaks over the last 18 months.

Unions claim that such accidents are often the first sign that an installation's integrity is in doubt and Taf Powell, head of the offshore safety forum, said there was "no doubt" that maintenance spending had been held in check.

Suggestions that oil and gas companies have continued to cut back is politically sensitive at a time when they are notching up record profits and handing back billions of pounds a year to shareholders via buy-backs. Talks between Conoco and Burlington Resources, the natural gas company, over a $30bn takeover also suggest that firms want to spend their money on mergers and acquisitions.

The oil companies categorically deny that safety is being compromised, but BP was accused of poor maintenance at its Texas City plant and fined $21.4m for 300 safety violations.

BP has also been in trouble this year for failing to report a spillage in Alaska and was forced to pay out a record $81m in an air quality lawsuit over emissions from a refinery in California. Last night the company defended its record saying it recognised there had been room for improvements, especially after its expansion into the US through the takeover of Amoco and Arco.

"Exxon has been traditionally the leader in this field and we were way behind, but we have now caught up - Texas City apart," said a BP spokesman.

However, Buncefield will no doubt bring the spotlight back on an industry that has just been hit by an extra £2bn a year tax bill from the Treasury.

Accident toll

March 23, 2005 The BP refinery blast at Houston, Texas, killed 15 and injured 170. BP has since set aside $700m for compensation. A report found workers' trailers were too close to a refinery unit - all the people killed were in the trailers at the time.

August 14, 2003 Eight workers died when petrol tanks exploded at Repsol's refinery in Puertollano, Spain.

September 21, 2001 An explosion destroyed the AZF fertiliser factory in Toulouse, France, killing 29 and injuring hundreds. The plant, owned by TotalFinaElf, had been opened in 1924 in countryside, but became surrounded by urban sprawl.

April 16 2001 ConocoPhillips' Humber refinery exploded when a gas cloud from a failed pipe ignited. There were no fatalities.

March 2001 Ten were killed by explosions on the world's biggest offshore oil platform, belonging to Brazil's state oil firm Petrobras.

July 1988 In the world's worst oil rig disaster, 167 were killed when Occidental Petroleum's Piper Alpha North Sea rig exploded after a gas leak.