The black clouds emitted by last December's massive fire at Buncefield Oil Depot caused no serious risk to health, according to reports published this week.

The announcements, made by the Department for Environment, Food and Rural Affairs and the Health Protection Agency (HPA) together with local primary care trusts, stated that the blast, near Hemel Hempstead, did not cause widespread pollution or lasting public health risks.

Firefighters from Borehamwood and Radlett attended the fire, which sent a cloud of smoke over south Hertfordshire. Schools in the area were closed as a result.

Nearly 250 people went to Accident and Emergency departments, most on the day of the fire. About 75 per cent were emergency workers, mostly for routine check-ups, and there were 38 members of the public who had symptoms of minor respiratory complaints.

A separate report, also published this week, revealed the cause of the blast to be a broken safety gauge which allowed a tank of unleaded petrol to overflow.

The cause was established in an ongoing independent investigation into the blast. It stated the overfilling of a tank 912' led to an escape of fuel causing the formation of a cloud of flammable vapour.

Further study is needed to fully understand how it ignited and why it exploded with so much force, causing so much damage.

However, there is still an ongoing criminal investigation into the blast, which means certain details cannot be published in case they influence a potential trial.

No one has yet been prosecuted.

Governmental bodies the Health and Safety Executive and the Environment Agency are currently drawing up new safety recommendations in relation to the design and the operation of similar sites.