Oil company chiefs denied today that there had been leaks before yesterday's massive depot explosion.
A Total spokesman said it was "too early to say" what had been the immediate cause of the blast.
But, in a statement, the company denied reports that there had been recent leaks at the plant.
It said: "Following media reports of foam leaks being seen at the Buncefield oil depot in recent days, Total UK wishes to confirm that foam is routinely discharged at the depot as part of ongoing safety checks.
"It is not unusual to see foam at oil storage depots, since regular discharge of foam forms an important part of checking safety procedures.
"The company categorically denies there were any product leaks, as suggested by some media reports, prior to the fire and explosion which took place on Sunday December 11."
The blast at the Buncefield oil depot near Hemel Hempstead, in Hertfordshire, has been described as the biggest in peacetime Europe.
Firefighters were given the go-ahead to begin tackling the flames this morning, more than 24 hours after fire first tore through the complex.
They will attempt to create a "foam blanket" to put out the huge inferno using 250,000 litres of foam mixed with 25,000 litres of water per minute.
The blast at the site, one of the largest oil supply depots in Britain, has sparked panic buying among some motorists.
But oil industry managers said they have plans to deal with such an emergency.
Ray Holloway of the Petrol Retailers Association said: "I understand the concern of motorists, but there is no need to panic."