Fuel explosion throws a giant shadow across England

• Water and land quality could be badly affected across southern England

• Clean-up operation to cost hundreds of millions of pounds

Key quote

"The tank could have been maliciously blown up, but the security on these sites is enormous. More likely, it's either a catastrophic tank failure or control failure of the pipeline” - Hans Michels, professor of safety engineering at Imperial College London

Story in full ANALYSTS were last night trying to assess the environmental impact of a fuel depot explosion that caused the biggest industrial fire since the end of the Second World War as a vast cloud of smoke threatened to dump oil residues over large tracts of south-east Britain.

The explosion at the Buncefield fuel terminal outside Hemel Hempstead, Hertfordshire, yesterday morning ignited millions of gallons of fuel and sent a thick plume of smoke across southern England and towards the Channel.

The fires could burn for days and the cost of the disaster and the subsequent clean-up operation is expected to run into hundreds of millions of pounds.

The Environment Agency said the main areas of concern involved the potential for pollution to groundwater, rivers and streams and also damage to land quality which could occur if any of the substances, including kerosene, diesel, gas oil and gasoline, were to escape.

Meteorologists also warned that soot falling in rainfall could contaminate grazing land. Peter Kidds, a forecaster at the Met Office, said it could result in milk from the south-east of England being un-usable. "This is going to affect grazing animals because the grass could be contaminated," he said.

The explosion happened shortly after 6am, ripping through the fuel terminal in Leverstock Green, close to Junction 8 of the M1. Despite the severity of the blast, which sent flames shooting hundreds of feet into the sky, only two people were seriously injured among 43 casualties.

The force of the blast was such that it could be heard up to 100 miles away, prompting fears of a terrorist attack or a plane crash, but Hertfordshire Chief Constable Frank Whiteley said police were treating the incident as an accident, despite the appearance on the internet four days ago of an al-Qaeda videotape calling for attacks on facilities carrying oil.

A security guard working at a nearby building reported smelling fumes moments before the blast. Raheel Ashraf said: "It was really bad. I had popped my head outside and smelled it there too, then it was difficult to tell if the smell was coming from inside or outside the building."

He said that moments later there was a massive explosion. "It was awful. It was like you were in hell. The flames were as high as 200ft and kept rising. You could literally see the fire growing."

The depot - which holds millions of gallons of various fuels - also supplies Heathrow and Luton airports.

About 2,000 people living nearby were evacuated, while police advised others to keep windows and doors closed because of the thick plume of smoke rising, clearly seen by satellite pictures as a thick blob dispersing east, west and southwards.

Experts believe that the explosion may have occurred after fuel leaked from one of the tanks and vaporised.

Dr Clifford Jones, of Aberdeen University, said: "It might be that some gasoline exited the storage vessel to form vapour a great deal denser than air which, having escaped, would not be protected by the safety features of the storage container."

Hans Michels, professor of safety engineering at Imperial College London, said that although a malicious act, including terrorism, could not be ruled out, it was most likely to have been caused by either a crack in the wall of a tank or a computer problem with the oil pipeline.

He said: "The tank could have been maliciously blown up, but the security on these sites is enormous. More likely, it's either a catastrophic tank failure or control failure of the pipeline. In a failure of the tank wall, an undetected crack can appear which, with the pressure of the fuel inside, can split from bottom to top in less than half a minute."

He said the escaping liquid would have the power of a burst dam, quickly covering an area the size of two football pitches to a depth of two feet.

"The vapour would separate quickly in the open air and a large cloud would form. Mixed with the air, the vapour becomes highly explosive and an ignition source such as a car engine or a hot pump, as is always possible on sites like these, is enough to start the explosion," he said.

"The other possibility is a pipeline failure. If a valve is not closed by the computerised system, it is like leaving a bath to fill without turning the tap off."

Prof Michels said petrol explosions can also be caused by heat, so the first explosion would have led to the chain of explosions that followed and may still yet continue. "To stop more explosions, you can only take the air away, but that is a massive operation. The site is surrounded by a dyke and you have to let it burn until it stops."

Each of the 20 tanks on the site is believed to hold three million gallons of fuel, worth an estimated 10 million.

The site is jointly operated by Total and Texaco. Texaco was also involved in the 1994 explosion in Milford Haven, which injured 26 people. The company was later fined 100,000.

Other companies have also been fined heavily after explosions at fuel facilities. BP was fined 750,000 for two explosions at the Grangemouth refinery in 1987 in which three people died. Shell was twice fined 100,000 for incidents at Stanlow and Shellhaven in 1990 and 1991.

The Piper Alpha explosion and fire in 1988, which killed 167 workers, remains Britain's worst oil industry disaster.

Hertfordshire's Chief Fire Officer, Roy Wilsher, said yesterday's blast was "possibly the largest incident of its kind in peacetime Europe".

He said about 150 firefighters - some drawn from outside Hertfordshire - would tackle the blaze in stages through the night, dealing first with the smaller fires and then attacking the major blaze.

About a quarter of a million litres of foam concentrate was sent to Hertfordshire from other parts of the country to help tackle the flames and Mr Wilsher said firefighters would be pumping liquid at a rate of 25,000 litres a minute.

He said water would be drawn from as far away as the Grand Union canal, two miles from the blaze.

Although the Buncefield site is Britain's fifth-largest, the oil industry said that there was unlikely to be any effect on fuel supplies or prices. The Petrol Retailers' Association said the only risk was from panic buying. Its director, Ray Holloway, said: "I know there are queues of panic buyers in the immediate area and in north-west London, but I've also seen people queuing in Croydon in south London - that is just bizarre. Frankly, there are better ways to spend a Sunday."

Airport operators also said they did not anticipate problems. Heathrow and Luton airports said they had made alternative supply arrangements.

Some flights were delayed because of smoke drifting across Heathrow.

But there was good news for owners of homes and businesses damaged in the explosion. The Association of British Insurers said they would be covered.

John Prescott, the Deputy Prime Minister, visited the scene of the blasts and said he had been impressed by the work of the emergency services.