Twelve months after a massive explosion ripped through the Buncefield oil storage site in Hemel Hempstead, Hertfordshire, what is now known about the blast's causes and its impact?
Some 2,000 homes were evacuated and 92 neighbouring firms were affected by Europe's largest peacetime fire. As a plaque is unveiled to mark the first anniversary, what has been learnt since?
The Buncefield Major Incident Investigation Board was set up to supervise the inquiry into the fire and make recommendations for the future.
Collecting evidence was tricky
Three areas are being considered by the Health and Safety Executive and the Environment Agency.
Officials are looking into possible criminal charges; reviewing policies for regulating on-site activities, and seeking to identify the root causes of the incident and the lessons to be learned.
Investigators say the devastation of the site and the resulting problems in collecting evidence has made Buncefield more difficult to probe than most major incidents.
"Local residents and businesses have continually demonstrated strength and determination to overcome the devastation and changes to daily life which have been caused by the explosion," said Lord Newton of Braintree, the chairman of the investigation board.
"The Board is aware that great uncertainty remains and continues to work extremely hard on reaching its own conclusions and recommendations."
FINDINGS TO DATE
An initial report published in July identified areas of concern connected to the design and operation of storage sites, the emergency response to incidents and advice given to planning authorities about risks to proposed developments around depots similar to Buncefield.
Investigators said an apparently faulty gauge and safety devices led to the overfilling of fuel storage tank 912 leading to an escape of unleaded petrol and the formation of a cloud of flammable vapour that ignited.
Future reports will aim to identify why the overfilling took place and what caused the explosion to be so powerful.
A separate report by Hertfordshire Fire Service, which was aided in the emergency response by crews from across England, came up with 30 recommendations.
Among these were suggestions for a national system of incident command support teams, earpieces for radios to enable communication while wearing a helmet and a proposal that early consideration needs to be given to deployment of national resources.
FUTURE OF SITE
The twisted wrecks of the fuel tanks have been left on site as the investigation continues.
Large parts of the depot have been destroyed and operators Hertfordshire Oil Storage Limited - a joint venture run by Total and Texaco - and the British Pipeline Agency have yet to formally announce on any long-term future plans.
Large parts of the depot were destroyed in the blaze
If the firms wish to resume operations they will need to satisfy planners and health and safety agencies that their procedures are low risk.
Rebuilding on the site would also require the relevant consent from Dacorum Borough Council and the HSE and EA.
Part of the site run by BP is located furthest from the fire and appears to have escaped with very limited damage.
BP has said storage operations could begin again on a reduced scale by the middle of 2007 and it was looking at the possibility of reopening its fuel pipelines to Heathrow airport.
Total, meanwhile, has submitted plans to link existing underground pipes to supply Heathrow.
The clean-up of 26 million litres of stored contaminated water used to fight the blaze, as well as ground water contaminated by diesel entering a borehole, remains a concern.
During the year some 800,000 litres of stored water was found to have leaked into the Colne, a tributary of the Thames, from the Blackbird sewage treatment works.
Environment Agency officials became aware of the presence of perfluorooctane sulphonate, or PFOS, a toxic substance used in some firefighting foams that does not break down in the environment.
PFOS is being phased out but the amount of foam needed to contain the Buncefield blaze saw old stocks brought in.
Special treatment and disposal of the most contaminated firewaters, stored at the Maple Cross treatment works, started in November.
Environment Agency officers will inspect the operation and ensure the treated water is clean before any discharge occurs.
Three Valleys Water, meanwhile, has been undertaking trials of pumping water from their borehole through treatment works for discharge into the river. However, this will not be used for drinking water.
Environment Agency manager Colin Chiverton said more than 750 groundwater, surface water and soil samples had been taken during the year and an extra seven boreholes had recently been installed.
"We are satisfied that the oil companies' method for disposing of the contaminated firewaters prioritises the protection of the environment," he said.
"However, we will continue to inspect and monitor the treatment operation to ensure the environment is protected."
An initial report on the results of the air quality monitoring concluded there was unlikely to have been widespread impact at ground level.
The Department for the Environment, Food, and Rural Affairs also found the fire did not result in substantial pollution of soil.
No-one died in the blast but two people on the site suffered serious injuries.
The Health Protection Agency concluded there was no evidence of a public health risk from the plume - either as deposits or on air quality.
The fire's plume could be seen across large parts of the south
It said of the 244 people who attended A&E departments, three quarters were from the emergency services. Of the total figure, 90% were sent home without needing follow-up appointments and most of the others had minor injuries.
The HPA found anxiety among the public dropped from approximately 50% at the time of the incident to 13% by February 2006.
"Buncefield was clearly a major emergency, but luckily the public health impact was rather small," said Professor Pat Troop, chief executive of the agency.
"The situation could have been very different if the initial explosion had happened at a different time, or if the weather conditions had been less favourable for dispersing the plume."
Dacorum Borough Council said 2,000 homes were evacuated during the fire.
One year on, two families remain in temporary local authority accommodation while
an estimated three families are likely to be spending a second Christmas in a hotel.
Ian Silverstein is still waiting for compensation claims to be settled
A survey of 761 private householders in the area surrounding Buncefield suggested 76% had experienced some damage. This mainly comprised broken glass, damaged window and door frames, roofs and cracks in walls and ceilings.
The majority of households were able to claim against their insurance for damage but some claims are yet to be settled and repairs to some homes have still not been completed. As the year went on, some households reported new and further damage.
A number of people are also in rented accommodation, among them designer Ian Silverstein who says he is still waiting for compensation.
Mr Silverstein says his £1.3m property located just over 100 metres from the depot was left uninhabitable.
Hemel Hempstead MP Mike Penning has accused the site's owners of "being pedantic beyond belief" in settling claims.
"There are probably 20 or 30 people who are still not back at home. People
living in houses that have been damaged are into the thousands," he said.
Hertfordshire Oil Storage Ltd said it has established a committee to oversee the management of claims.
Compensation claims against the site owners are to be settled by negotiation or mediation, without admission of liability.
Some 3,300 claims, worth a potential £700m, have been filed by individuals, loss assessors and companies.
Of the claims, there are about 250 from individuals, which total £20m, and 2,754 out of the 3,300 claims are for less than £10,000.
Some 92 firms on the Maylands business park, employing about 9,500 people, were directly affected by the explosion.
Most firms remain committed to the Maylands business park
One year on, 14 businesses employing about 200 people have relocated and several are still operating from temporary premises. Two businesses employing 25 people in total have gone into liquidation.
But the majority of the 630 firms remain committed to Maylands.
Many businesses whose premises were severely damaged - including Kodak, ASOS and DBD Kitchens - have already moved back and a strategic plan to rejuvenate the business park is in under way.
The incident cost firms more than £70m, according to a study by the East of England Development Agency.
Meanwhile, one firm reckons some UK businesses devised "impractical" continuity programmes in the wake of Buncefield.
"The problem is companies now blindly believe in the plans they have in place, so boards are reluctant to invest further," said Richard Potter from Maylands-based IT services firm Steria.