Police are talking to a tanker driver who may have accidentally ignited a fuel depot explosion that injured 43 people, damaged nearby buildings and sent black clouds as far away as France, fire investigators said Wednesday.

Investigators say the fire still appeared to be accidental but they were looking into several possible causes, including a tanker driver whose engine may have ignited fumes at the Buncefield depot in Hemel Hempstead, northwest of London, early Sunday.

"We're speaking to this driver," Hertfordshire Police Assistant Chief Constable Simon Parr said as firefighters continued to battle one of the remaining blazes at the depot.

The Sun newspaper reported Wednesday that a person who worked with the tanker driver said the fuel facility was riddled with safety hazards, calling it a "ticking bomb."

Although it was still unclear what ignited the blaze, it was clear there was "a release of fuel," said Bob Woodward of the Health and Safety Executive, a government body investigating the cause of the explosion.

Two warnings were given to the plant in the past six years, but Woodward said he had no "grave concerns" about the site before Sunday's explosions.

A notice was issued in 1998, he said, which related to a required fire certificate for an office building. A second notice was issued in 2001 for the construction of a safety wall around the site's largest tank, which was the last of the fires to be extinguished by firefighters Tuesday night.

The Sun spoke to a man who said drivers routinely took banned battery-powered items into the plant and that there were multiple safety hazards, including drivers who left their engines running.

"Drivers are spoken to and notices put up, but it's allowed to continue," he told The Sun. He was not identified.

He said the driver told him he drove into the plant Sunday, got out of the truck and then smelled an odor. He allegedly ran back to the tanker and flipped a switch off. It was unclear what type of switch he was referring to.

"His engine cut out — then boom! He does not know whether he caused it but he blames himself," The Sun quoted the tanker driver's colleague as saying.

Although there were no deaths from Sunday's blaze, more than dozen buildings were ruined and about 20,000 workers were not allowed to return to their jobs in the industrial park after the fire — one of the largest in Europe since World War II.

Most evacuated residents were allowed to return to their homes but officials said it could take more than a decade to rebuild the industrial park and clean up Hemel Hempstead, 25 miles northwest of London.

The depot stored 4.2 million gallons of gasoline, diesel, kerosene and aviation fuel.

The series of explosions came four days after an Al Qaeda videotape appeared on the Internet calling for attacks on facilities carrying oil, but officials drew no link between the two events.