As residents and businesses around Buncefield oil depot begin assessing the damage following explosions and fire at the site, the local MP has condemned planning laws that allowed construction so close.
What are the laws governing the location of sites handling hazardous substances?
Any plan to build a site handling hazardous substances above a level specified by the government requires consent from the hazardous substances authority, usually the local authority.
It must seek advice from the Health and Safety Executive (HSE) and Environment Agency on "residual risks" associated with the proposal even after all reasonable steps have been taken to ensure safety.
Experts say the cost to nearby businesses could be "multi-millions"
The authority then has the final decision on whether to approve the plan.
How is development around existing hazardous sites regulated?
The HSE decides on the size of a "consultation zone" around sites, based on the nature and quantity of hazardous substances allowed there.
The local authority must then seek the advice of the HSE when there are proposals for certain types of development within that zone.
Proposals requiring HSE consultation include: all residential development; retail, office and industrial premises above a certain size; and any other development likely to increase the number of people working within or visiting the area.
The HSE's role is again purely advisory, the final decision resting with the authority.
What are the authority's considerations?
The HSE acknowledges that for authorities facing such planning decisions, "safety, however important, is only one of the elements to be considered".
"There are few locations where new hazardous installations can be 'shoehorned' into place without creating some risk to an existing community," says the HSE.
"The UK is a small, densely populated island and such undeveloped areas as do exist are often so remote or of such environmental value as to be unsuitable for industrial use.
"It also remains the case that, to be economically viable, industries need to be sited where they are accessible to main transport routes and to sources of labour."
It adds: "A balance has to be struck between the needs of industry, the needs of the community and the interests of safety."
Could the planning laws change as a result of the Buncefield disaster?
Forty-three people were injured in the explosions and fire, two seriously, and insurance assessors have warned the cost to nearby businesses will run into "multi-millions of pounds".
Mike Penning, Conservative MP for Hemel Hempstead, said 60 major commercial buildings would need to be demolished because they were now structurally unsafe, and another 150 had suffered superficial damage.
But he added that thousands of people could have been injured if the blast had not happened early on a Sunday morning.
"We were very lucky this time - if it had gone off at 10 o'clock on a Monday morning there would have been 30,000 people inside the blast zone," Mr Penning said.
Some 30,000 people worked and 2,000 others lived within the area in which windows were shattered by the explosion, he said.
"I think this major national disaster will mean the need for a fundamental change in planning law that allows these sorts of depots so close to commercial and residential properties," he said.
A spokeswoman for the Office of the Deputy Prime Minister said it was too early to say whether the disaster would affect planning policy.
She said the department would await the findings of the investigation being carried out by the HSE and Environment Agency.