Flames from smaller, more manageable fires were still to be seen at dusk at the Buncefield fuel depot near Hemel Hempstead, 40 kilometres northwest of London.
But firefighters announced, not without a little relief, that they had finally succeeded in snuffing the blazes that had engulfed all 20 of the fuel tanks which had caught fire since Sunday's blasts.
The fire at the biggest tank, and toughest one to tackle, was the last to be put out with a blanket of foam, after two others were smothered early on Tuesday.
Health officials meanwhile continued to closely monitor the impact of the huge plume of smoke created by the fire, which was visible from space.
"There are still some small bund (concrete container) fires but the tanks are out," Hertfordshire chief fire officer Roy Wilsher said.
More than 600 firefighters have been involved in fighting the "apocalyptic" blaze, and Fire Officer Wilsher said many would remain for several days cooling the area to ensure that fires did not break out again.
Smoke concerns
The smoke plume, drifting southwest, was expected to fall to the ground during the night and local residents were warned to remain indoors.
With the inferno over for all intents and purposes, attention was shifting to the aftermath and how to cope with the clear-up.
Police said they had to begin the process of helping business owners, managers and residents back into their premises, apart from those living closest to the site.
Health official Jane Halpin said air quality sampling from around the site had not given any cause for concern.
"What they have identified is really just basic soot, no evidence of organic chemicals," she said.
Fire services minister Jim Fitzpatrick told BBC radio that the Health and Safety Executive would start its investigation into the causes of the incident "as soon as the site is secure".
The fire appeared to have started accidentally, although the cause remained unknown and clues as to what might have caused it were likely to be consumed in the inferno, police said.
Forty-three people were injured, but no one was killed.
Witnesses who saw the first blasts around 0600 GMT Sunday described them in apocalyptic terms, with one likening the scene to "doomsday".
Cooling off
A series of explosions tore sections of walls off buildings in an industrial park, smashed windows and dented doors of homes, ripped tiles from rooftops, burned trees and incinerated at least half a dozen cars over a wide area.
Firefighters have battled intense heat and smoke but also the risk of accidentally bringing down containers and triggering explosions.
After having spent all day Sunday cooling off seven tanks that had not caught fire, the firefighters began the mammoth task of extinguishing the blaze on Monday morning.
The real work was delayed until they had satisfied concerns that their foam and water mix would not pollute nearby ground water.
They also had to wait for around 250,000 litres of foam concentrate to be sent from around the country.
Work has also been interrupted twice due to the risk of more tanks exploding, including one feared to contain volatile substances.
The depot, jointly run by French oil company Total and Texaco, part of US oil giant Chevron Corporation, was able to store up to 150,000 tonnes of fuel, which was distributed to airports in the London area.
The fire caused widespread traffic disruption including closing down sections of the M1 motorway that links the British capital with the north of England.