BioEd Online

A series of explosions at an oil depot just north of London has created one of the biggest industrial fires ever seen in Europe and injured 43 people. Starting at about 6:00 GMT on 11 December, a thick pall of black smoke has spread from the Buncefield oil depot in Hemel Hempstead, Hertfordshire, for more than 120 kilometres across southern England. As the fire rages on, Nature investigates efforts to damp the blaze, and asks about the environmental and health effects of the smoke.

How did it start?

No one knows for sure, but police say they have no reason to suspect foul play.

How serious is it?

"Any incident that you can see from space is not your average garden bonfire," says Zäl Rustom, who works for Hi-Bar UK, a pollution-response company in West Sussex. "It's major."

But he adds that the fire now seems to be under control, and pipelines supplying the facility were shut off immediately after the explosions.

Firefighters have 250,000 litres of foam concentrate at their disposal. This is added to water to make a thick blanket that starves a fire of oxygen. "The main problem now is the logistics of getting foam on top of the tanks," says Rustom.

Roy Wilsher, Hertfordshire's chief fire officer, told a press conference on 12 December that it was impossible to say how long the blaze might burn. "We are in uncharted territory," he said. "This is the largest fire of its kind that we in the UK, and in Europe, have dealt with."

What is burning?

Up to 270 million litres of kerosene, diesel and gasoline, held in 20 storage tanks on the site. Half of those tanks' fires have now been extinguished.

The facility is co-owned by Total and Texaco, but also used by oil companies such as BP and Shell. Much of the fuel at Buncefield is transported by train and pipeline to the nearby airports at Luton and Heathrow.

What pollution is it producing?

Smoke, mostly. And a research aircraft is now trying to find out more.

"We're flying around the extremities of the plume as far as we can," says Steve Ball, who heads the Facility for Airborne Atmospheric Measurements, based at Cranfield University in Bedfordshire. The plane is normally used to monitor urban pollution, part of a joint project between the Met Office and the Natural Environment Research Council (NERC).

Today it is tracking the speed and shape of the cloud. The Met Office hopes this will help its researchers to forecast the plume's path. The cloud is currently being blown southwest.

Researchers hope that the plane will return tomorrow with additional equipment that can sample the gases and particles in the smoke. Carbon monoxide, carbon dioxide, sulphur dioxide and oxides of nitrogen are all pouring from the fire, along with tiny flecks of soot.

"There will be hundreds of different molecules in there," says Met Office meteorologist Wayne Elliott. "And the smoke may continue even after the fire is out," he adds.

What are the health effects?

Health Protection Agency officials are advising that the smoke is likely to affect only those with existing respiratory problems, such as asthma. For those bothered by the smoke, staying indoors is the best precaution, they say. Colbeck adds that unless a person's exposure is exceedingly high, a one-off incident such as this shouldn't trigger any long-term health problems.

Once the fire is out, local air quality should return to normal levels within a few days, says Ian Colbeck, an expert on the role of aerosols in the environment at the University of Essex, Colchester.

What are the environmental effects?

The cloud will contain pollutants known as polyaromatic hydrocarbons (PAHs), but it is unlikely that they could accumulate to a high enough concentration to cause severe environmental effects, says Dan Osborn of NERC's Centre for Ecology and Hydrology in Lancaster.

"There's nothing in the cloud that isn't already in the environment," adds Osborn. The plume is also too small to have any direct effects on climate.

England's rainy weather may also help to disperse the pollutants, spreading material over a wider area at lower concentration, so that toxic effects are less likely to build up. "If it does rain out, it should be less of a problem," says Osborn.

The biggest potential difficulties could be caused by attempts to put the fire out, he adds. "When a mass of water goes into the ground, it can flush older contaminants out," Osborn says. "There has also been concern in recent years about the materials in fire-fighting foam." So the run-off mixture of foam, water and fuel will be contained within temporary reservoirs to avoid contaminations of water supplies.