Today, the firms behind the Buncefield fire will be held to account. But will they be made to pay?

It has taken five years, but today the companies whose negligence caused the biggest fire ever seen in Europe in peacetime and almost destroyed a thriving community around the Buncefield oil depot will face justice.

The fines meted out to the five companies are likely to be the highest ever imposed under health and safety and environmental legislation.

The explosion and resulting fire in Buncefield, in south Hertfordshire, in December 2005 is reckoned to have cost £1bn in damage to property and the environment, as well as lost business and lost jobs in the vicinity. That excludes any measure of the trauma suffered by people uprooted from their homes after the terrifying explosion.

Though today's sentencing brings the criminal case to a close, civil proceedings continue. Only tiny sums have been paid so far to those whose lives were overturned by the disaster.

At a time when government quangoes face unprecedented cutbacks, the verdict is a triumph for two public bodies – the Health and Safety Executive and the Environment Agency – who painstakingly traced the cause of the fire and prosecuted the companies.

The local council, Dacorum Borough Council, set up a disaster fund for the victims, which received almost £80,000 from local voluntary groups, and £621,750 from Total UK, the French oil giant that has admitted responsibility for the disaster, and from its part owned subsidiary, Hertfordshire Oil Storage Ltd, which runs Buncefield.

In the first quarter of 2010, Total Oil reported profits of €2.61bn (£2.18bn), so their contribution to the disaster fund was "a tiny fraction of the oil companies declared profits over the same period," said Daniel Zammit, chief executive of Dacorum Council. "Of the 2,266 grants awarded from that fund, most were around the £100 mark, and the fund is now nearly exhausted."

Total Oil pleaded guilty to three charges of failing to protect staff and causing pollution. The other companies – Hertfordshire Oil Storage, the British Pipeline Agency, TAV Engineering and Motherwell Control Systems, which has gone into liquidation – were all found guilty by the jury in a trial that ended last month.

The explosion was heard as far away as France and Belgium. It set off a fire that raged for four days, sending up smoke that could be seen from space.

It happened because electronic equipment in one of the storage tanks failed. Neither the gauge which should have warned the control room that the tank was full, nor the switch which should have automatically closed the pipeline supplying the tank worked. As a result, 250,000 litres of petrol – enough to fill eight tankers – poured to the ground, creating a thick vapour.

The first to notice something was wrong were motorists whose cars behaved strangely, continuing to rev up after the engines had been shut off. The huge vapour cloud exploded just after 6am, damaging houses and industrial buildings.

As the fire spread, 2,000 people had to be evacuated, including six families who were still in temporary homes months later. There were 43 people injured. More than 1,000 jobs were lost in the area because the damage to a nearby industrial estate forced companies to relocate. The water table below Buncefield is still polluted with fuel and foam used by firefighters to put out the fire. Readings taken by the Environment Agency from a bore hole have turned up alarming results. On 1 February this year, inspectors noted a "strong odour and black particles" in the water table. Two days later they detected "a strong petroleum smell".

Howard Davidson of the Environment Agency stressed that the drinking water in the area was safe, but said there was pollution in the water table which would take years to clear up.

"The incident has left behind a considerable legacy," he said. "Chemicals found in petrol, such as benzene, and firefighting foam, continue to be detected in the chalk aquifer under the site and in groundwaters up to two kilometres away.

"Once groundwaters become polluted they are difficult to remediate and modelling indicates that we will continue to see current levels of pollution in the aquifer for many decades to come."

Mike Penning, Tory MP for Hemel Hempstead, said: "I see people every week – every single week – who are still suffering because of Buncefield. We had people that lost their homes, jobs, everything. After four and a half years, we are about to see some of the justice done that my community deserves."

The largest fine ever imposed in the UK in a criminal case involving pollution was £4m that Milford Haven Port Authority was ordered to pay by a High Court in 1999, after a Russian tanker, the Sea Empress, ran aground and spilled oil along the Welsh coast.

The fine was reduced on appeal to £750,000. The highest this decade was £190,000 imposed on Anglian Water in 2002 for a series of water pollution offences at its Stewartby sewage plant in Bedfordshire.

Case Study: Terror in the night changed our lives

What continues to haunt David Mitchell five and a half years after the Buncefield fire is not so much what actually happened, but what might have been.

He was awoken just after 6am by a noise so loud he thought a jumbo jet had crashed into his house.

After the bang, there was a strange whooshing sound as air was sucked back into the vacuum created by the explosion, followed by the clatter of falling tiles.

The most terrifying sight was in the bedroom – occupied by his son Henry – which was closest to the depot. There was a long crack in the bedroom wall, part of which was at a peculiar angle. A large part of the roof had come crashing down, exposing the sky and narrowly missing the sleeping child.

"He could have died," Mr Mitchell said. "When I was treated for post-traumatic stress, it wasn't over what happened, so much as what nearly happened."

Fortunately, the way the debris fell left a narrow tunnel and Henry was able to crawl to safety. Seconds later, his father was trying to find out what had happened.

It was then he realised the noise had come from Buncefield, where flames of unbelievable size and brightness were belching from the storage tanks. From outside he could see that the top half of Henry's bedroom wall had been ripped outwards by the air being sucked back. Neighbouring houses had suffered in similar ways.

"Doors and windows had been sucked out, rather than blown in," he said. "The explosion had done the damage, weakening everything, then the backdraft ripped them out. One of our neighbours had a wreath on their front door. They found the wreath in their hall and the door in the courtyard. The door had first been blown in, then sucked out."

Mr Mitchell and his wife Lisa grabbed some clothes and their car keys, collected Henry and his five year old sister, Alice and drove off.

Strangely, despite being less than a mile away from the biggest fire seen in peacetime Europe, Mr Mitchell has no recollection of being hot. Neighbours said they recalled the heat, but he remembers that there was ice on the car.

It was December and the family were facing days of homelessness.

They finally returned home for good on 23 December, after 12 days of makeshift accommodation provided by the council, but were soon wondering if it was a good idea.

"We wanted to be back for Christmas, because we did not want to make too big a deal of it. We wanted the children to think it was an adventure rather than a disaster," Mr Mitchell explained.

"The insurance company reacted very quickly, possibly because they realised it would cost them less if the work was done quickly, but it was a bit of a nightmare. We had builders in every room. I was living in the dining room. It was April the following year before the last job was finished. We should have stayed out for six months."

The Mitchells were luckier than some of their near neighbours.

Their home is about 500m from the depot boundary across a field. Three homes on the other side of the field – just a few metres from the boundary fence – had to be abandoned permanently.

One elderly couple happened to be downstairs at 6am when their house collapsed around them. Had they been upstairs, it is unlikely they would have survived.

After months of disruption the Mitchells got their house back – but how much value it has lost by being so close to the scene of a disaster nobody knows, because no house in the vicinity has successfully been sold since 2005. Mr Mitchell, who works as a freelance television producer, estimates their home was worth £650,000 back then, but may now be worth 10 per cent less just four and a half years later. The four members of the family were paid £1,000 each as compensation for their trauma, but for their financial losses have so far received nothing.

Buncefield timeline

10 December 2005 7pm

Hertfordshire Oil Storage Ltd begins pumping unleaded petrol into Tank 912

11 December 5.20am

Tank 912 is full. The supply of petrol should automatically stop, but doesn't

6.01am

Vapour from the leaked petrol explodes starting a fire that spreads to 20 tanks

12 December Midday

The fire, at its worst, is seen for miles

15 December

The fire burns out. Displaced families are allowed to revisit their damaged homes

16 December

The Health and Safety Executive opens an investigation into the cause of the fire

23 December

Investigators seize computer records and other evidence from control room

5 January 2006

Tony Newton, the former Tory Leader of the Commons, to head the investigation

February 2006

Investigators enter site where fire started

September 2006

Royal Mail moves offices from near Buncefield, and sacks 144, bringing total redundancies from the fire to 923

6 October 2008

Total Oil, which had disputed liability for claims for damage, backs down at the opening of a civil action in the High Court

16 December 2008

The civil action against Total Oil and others is ended after 30 days

20 March 2009

High Court rules that Total Oil had been negligent, but exonerates Chevron, the other major oil company in Buncefield

13 November 2009

Total Oil pleads guilty to three breaches of health and safety and environment regulations

18 June 2010

TAV Engineering, a contractor, convicted of negligence at St Albans Crown Court. Hertfordshire Oil Storage Ltd and the British Pipeline Agency also found guilty

16 July 2010

Five firms responsible for the explosion sentenced in St Albans Crown Court