HEMEL HEMPSTEAD, England — Firefighters used chemical foam to extinguish part of the inferno raging today at an oil depot north of London, while investigators searched for clues as to what caused the powerful explosions that started the blaze.

The blasts Sunday injured 43 people, sent balls of fire into the sky and blew the doors off nearby houses. The explosions, which police believe to be accidental, also contributed to a jump in oil prices by 55 cents today to nearly $60 a barrel.

The explosions came just four days after an al-Qaida videotape appeared on the Internet calling for attacks on facilities carrying oil that it claims has been stolen from Muslims in the Middle East. The incident rattled nerves in a country still jittery over the July transit terror attacks that killed 52 people and four suicide bombers.

Fire officials said they had put out blazes at half the 20 fuel tanks at the Buncefield fuel depot 25 miles north of London, the fifth-largest fuel depot in Britain. Authorities approved the use of foam to fight the fire after determining the runoff would not pollute ground water supplies.

Left to itself, the fire might burn for three days, said Roy Wilsher, chief fire officer in Hertfordshire county.

"We are in uncharted territory. This is the largest fire of this kind that the U.K. and Europe have dealt with," he said at a news briefing.

Most of the injured were treated for cuts and bruises from flying glass. One of two men with more serious injuries remained in a local hospital today, Hertfordshire police said. The other was released.

Chief Constable Frank Whiteley said police had yet to interview managers at the oil depot, and that the fire may have destroyed evidence leading to the cause.

"Although we continue to keep an open mind, there is nothing to indicate that this was anything other than an accident," Whiteley said. "It may well be that once the fire is out, there will be very little for our forensic teams to look at, but I think we will find out what happened."

The depot, operated by Total UK and part-owned by Texaco, stores 4.2 million gallons of gasoline, diesel, kerosene and aviation fuel.

Wilsher said firefighters were using nearly 8,500 gallons of water per minute from two different attack points to fight the fire. He said the wind was causing the smoke to swirl around the site, making conditions harsh for firefighters, who were within 100 yards of the blazing tanks.

About 300 people had been evacuated from their homes and taken to a bowling alley, which was being used as a shelter.