HEMEL HEMPSTEAD, England -- A fire raging at an oil depot in southern Britain sent toxic smoke as far away as France and caused jitters on the global oil market Monday as firefighters struggled into a third day to douse the flames with chemical foam.
Authorities said they believe the explosion Sunday at the Buncefield depot north of London was an accident, but will examine other possible causes, including terrorism.
After extinguishing fires in 12 of the 20 tanks initially ablaze, the 150 firefighters withdrew for five hours amid fears that one of the flaming tanks could contain highly volatile fuel, said Chief Fire Officer Roy Wilsher. His office said firefighters resumed their work after determining that the fuel in the tank was not as volatile as had been feared.
The terminal stores 4.2 million gallons of fuel, and the fire has caused unease on the oil market and raised questions about safety at the nation's oil facilities.
"There is nothing to suggest that it is anything other than an accident, but we're keeping an open mind and when we get into the site we'll treat it as a ... scene which could be a crime. We'll be doing full forensics," said Chief Superintendent Jeremy Alford of Hertfordshire police. "We'd be remiss if we didn't."
Firefighters battled the enormous fire for more than 30 hours before pulling back Monday. Authorities shut a highway nearby and extended a closed-off zone around the depot 25 miles north of London because of the chance the tank might explode, Wilsher said.
He said flames had reignited in one tank where they had been extinguished earlier.
"I don't want a human tragedy to go alongside the environmental tragedy that we've already got," he told reporters as firefighters withdrew.
Wilsher told reporters the firefighters were in "uncharted territory."
"This is the largest fire of this kind that the U.K. and Europe have dealt with," he said.
Police said the ferocity of the blaze would make it extremely difficult for forensic experts to determine its exact cause, but there was no indication of foul play. Chief Constable Frank Whiteley said eyewitness accounts and closed-circuit television footage would be key to the investigation.
The series of explosions came four days after an al-Qaida videotape on the Internet called for attacks on facilities carrying oil, but officials drew no link.
Deputy Prime Minister John Prescott told Parliament there would be a full investigation once the fire was extinguished.
"Does this latest incident prove that proper safety procedures were still not in place?" Conservative Party lawmaker Caroline Spelman demanded.
Gemma Shepherdson, a spokeswoman for Total U.K., which operates Buncefield, said security was tight and anyone entering the site had to go through a security gate and show a photo pass.
She said the depot was ringed by closed-circuit TV cameras.
Heavy plumes of black smoke continued to billow Monday from the depot, the fifth-largest in Britain.
Most of the 43 people injured in the blast before dawn Sunday were treated for cuts and bruises from flying glass. Two men with more serious injuries remained hospitalized Sunday night, and one was released Monday, police said.
The smoke cloud has drifted over Brittany and Normandy in northwestern France and was headed toward Spain, France's national weather service said Monday.
"Poison cloud hits London tonight," warned the Evening Standard newspaper.
Environment officials said toxins from the fire had not contaminated drinking water near Hemel Hempstead.
Most of the 2,000 people evacuated from their homes Sunday were still waiting to return.
David Smith, 65, an evacuee taking shelter in a recreation center, said he wa so't concerned about living so close to the depot.
"These places have got to go somewhere," he said. "It's a very small island; we need these oil depots."
Jane Hogg, mayor of Dacorum Borough Council, said authorities were trying to get people back in their homes as soon as possible, but needed to be sure the buildings were structurally sound.
The oil terminal explosions raised supply concerns, but authorities said the blasts would not lead to a shortage.
Oil prices surged above $60 Monday as forecasts of colder weather in the world's largest heating oil market, the U.S. northeast, boosted expectations of a rise in demand, and OPEC agreed to maintain its present output.
Representatives of oil companies, pipeline operators and the airline industry met Monday to discuss ways of keeping fuel supplies flowing. French oil firm Total S.A. said it had implemented contingency plans to reroute supplies that normally run through the plant.
"There shouldn't be any problem with supplies," said Lesley Else, a spokeswoman for Total U.K.
The Buncefield plant, which is part-owned by Texaco, carries jet fuel to Heathrow and Gatwick airports. It also stores gasoline, diesel and kerosene.