Hertfordshire Fire Service said crews had put out blazes at 10 of the 20 fuel tanks by midday.
But CBS News' Larry Miller reports weather patterns have changed: The heavy black smoke that Sunday blew away from the site, Monday was hanging over it, encompassing it, making it even more difficult for fire crews.
"We are in uncharted territory. This is the largest fire of this kind that the U.K. and Europe have dealt with," Roy Wilsher, chief fire officer in Hertfordshire county, told a news briefing.
"We are not even sure how the thermal current will affect the foam that is being applied — it might just vaporize it."
A thick black plume of smoke continued to billow from the Buncefield fuel depot 25 miles north of London, the fifth-largest fuel depot in Britain. Left to itself, the fire might burn for three days, Wilsher said.
The fire began with a series of explosions before sunrise Sunday. Shock waves tore off doors and bricks and shattered windows, reports CBS News correspondent Richard Roth. It was audible on the edge of London, 25 miles away.
"We didn't know what it was. We thought it was a bomb or an airplane going down," said one man.
Britain has been on edge since suicide bombings in London last July, and authorities' regular warnings that more terror attempts are inevitable. But while officials quickly said the explosions here seemed to be from an industrial accident, they still don't know the cause.
Most of the 43 people injured were treated for cuts and bruises from the flying glass of broken windows. Two men with more serious injuries remained in local hospitals Sunday night, and one was released Monday, Hertfordshire Police said.
Wilsher said 20 or more tanks at the facility had been destroyed, but that firefighters had managed to protect seven others through the night.
"We are using 32,000 liters of water a minute from two separate attack points," Wilsher told reporters.
He said firefighters were within a hundred yards of the blazing tanks.
"Conditions will be very harsh. They will be wearing breathing apparatus and protective equipment. They will be monitored by safety officers, and we will be bringing relief in all the time to make sure they are not in those conditions for too long," Wilsher said.
Hertfordshire police said earlier that the fire service, the Environment Agency and police were all satisfied that foam could be used without danger of polluting water supplies. There had been fears that runoff from the site could contaminate surface and ground water with fuel.
Chief Constable Frank Whiteley said Hertfordshire officers had not yet interviewed managers at the depot, and that the fire may destroy some evidence about 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," he said.
"I think there is enough evidence from the eye witnesses and closed-circuit television footage to enable us to do that."
The Buncefield terminal, operated by Total UK and part-owned by Texaco, stores 4.2 million U.S. gallons of gasoline, diesel, kerosene and aviation fuel.
Authorities are telling anxious drivers that gasoline is still plentiful, reports Roth, and they're trying to ease worries about the cloud of smoke: dense and vast and spreading over southeast England. Officials say it's not a lethal hazard, but using understatement as reassurance, one added: it won't be a good day to hang out the laundry.
The national Environment Agency said it was concerned that substances including kerosene, diesel, gas oil and gasoline could mix with the foam and escape from the site and pollute surface rivers and groundwater.
"We've come up with a plan that holds in that water on the site in walled areas, called 'bunded areas,' and we are having those areas monitored constantly," Wilsher said.
The series of explosions on Sunday came four days after an al Qaeda videotape appeared on the Internet calling for attacks on facilities carrying oil that it claims has been stolen from Muslims in the Middle East.
Noxious fumes from the fire, which left some people coughing, also affected the large squads of police who sealed off the area and evacuated nearly 300 people to a bowling alley being used as a temporary shelter.
Britain's deadliest oil-related disaster was the July 6, 1988, explosion and fire on the North Sea oil platform Piper Alpha, which killed 167 workers.
In 1994, a blast and fire at an oil refinery in Milford Haven, Wales, injured 26 workers and caused tens of millions in damage. Oil companies Texaco and Gulf were eventually fined for violating health and safety regulations.