Energy giant Shell has been fined �1m for breaches of health and safety and pollution controls following an explosion at its North Norfolk gas site at Bacton three years ago.

A three-day sentencing hearing at Crown Court heard a catalogue of failings that led to the explosion and pollution spilling into the sea.

Announcing the hefty fine at Ipswich court Judge Martin Binning said it was only by 'great good fortune' that there had been no deaths and that the accident had happened during the small percentage of the day taken up by a shift changeover.

'Fortunately neither death nor greater damage did occur which means the fines are less than they otherwise would have been,' he said.

The court bore in mind that the situation, over a long period of time, was allowed to become dangerous.

'No-one it seems to me, had really taken on board the situation that was occuring.'

The judge added: 'The total fines reflect public concern of the developing situation over the years which ultimately became dangerous.'

During the case prosecutor Andrew Marshall said management at the plant had been 'sleepwalking into danger' at the energy complex which provides about a third of the nation's gas.

The blast blew the concrete roof off the buffer tank of Shell's waste-water treatment plant, throwing concrete parts as far as 100m away. It took 70 firefighters from across Norfolk to deal with the subsequent blaze.

Mr Marshall said it was only by good fortune that staff were out of the way. Estimates were that 10 people could have been killed, not taking into account other possible serious injuries.

The judge was told during the hearing that management had been warned many times by workers about the high levels of a highly-inflammable chemical, North Sea Condensate, which ultimately caused the explosion.

Investigators traced the cause of the explosion to a leak of highly flammable hydrocarbon liquid into a part of the plant responsible for treating waste water before discharging it into the sea.

The leak was caused by the failure of a corroded metal separator vessel, which allowed water contaminated with the highly flammable condensate to enter a concrete storage tank where it was heated by an electric heater. The heater's elements were exposed within the tank, raising the surface temperature significantly causing the explosion and fire.

Following the blast an estimated 850 tonnes of North Sea Condensate, fire water and fire-fighting foam went into the sea.

Shell UK failed to close the sea gate until about an hour after the fire started. It also failed to notify the Environment Agency, as required, meaning that valuable advice on environmental protection during the incident or its aftermath was not available to either Shell or the fire service – an emergency response priority first identified in 2004. The delay in notification also meant an assessment of environmental harm was not possible.

After sentencing HSE Inspector Steve Johnson, said: 'The fact no-one was seriously hurt in this incident was solely down to good fortune as the company's internal report acknowledges. Shell UK neglected basic maintenance leading up to the explosion.

'Our investigation found key components had been failing for some years and the company knew this, yet there had been no appreciation of the potential for an incident such as this.

'In particular there had been no attempt to assess the risk that arose from condensate entering the water treatment plant despite the fact that the plant was not designed to handle highly flammable liquids like condensate.

'The investigation revealed significant failings in the safety management system operating on the plant and hopefully other operators will take note of the outcome of this incident and maybe review their own procedures.'

Environment Agency Environment manager for Norfolk and Suffolk Marcus Sibley said:

'We are disappointed that a company such as Shell with its experience in the fuel industry should have operated in this fashion.

'This is a high risk industry and that is why we expect high standards.

'The explosion could have led to a major environmental disaster as other highly flammable materials were stored nearby.'

Shell UK refused to answer questions outside court, but in a statement the company said: 'What happened was completely unacceptable and falls well below the standards that we set for ourselves.

'Safety is our company's priority and so an incident like this is deeply disappointing.

'We have admitted our fault, accepted the penalty and learned the lessons.'

Shell, which stressed that there was 'no threat to the safety of the local community nor the security of UK gas supply' said that a direct result of the investigations a significant number of improvements have been made.

Around �3m had been invested in reviewing operations processes, safety and integrity systems and a new waste eater treatment plant is to be built with a design including improved safety features.

The charges admitted by Shell related to breaches of the Health and Safety at Work Act 1974, Environmental Protection Act 1990, and Pollution Prevention and Control Regulations 2000.

They were:

Count one: failing to take all measures necessary to prevent major accidents and limit the consequences to people and the environment. Fined �150,000

Count two: failing to ensure the health and safety, and welfare, at work of its Bacton site employees. Fined �150,000

Count three: failing to ensure that people not employed by Shell were not exposed to health and safety risks. Fined �140,000

Count four: failing to maintain plant and equipment, namely separator vessel VG110 and associated equipment, in good operating condition. Fined �140,000

Count five: failing to notify the Environment Agency on the failure, or malfunction, of the separator vessel VG110 which could case significant pollution. Fined �140,000

Count six: failing to comply with a pollution prevention control permit by failing to prevent emissions of run-off and fire-fighting foam on February 28 2008. Fined �140,000

Count seven: failing to provide staff with sufficient training and levels of competence properly to operate Environmental Waste Treatment Plant between May 2007 and February 2008. Fined �140,000

Shell has also been ordered to pay the �242,000 costs of the case, and a standard �15 victim surcharge.

?For the full story and background see tomorrow's EDP.