One of Britain’s biggest energy firms has been fined £1m after a worker was almost killed when he was trapped for an hour in a gas cloud.

The fire service engineer was part of a team called out to reports of a gas leak in Scunthorpe when the incident happened.

While they were working in a 10-foot hole, the pressure of the escaping gas suddenly rose, rupturing the pipeline.

Video footage taken at the time of the accident, in June 2014, shows that fire crews were unable to see for the cloud of dust and debris created as they tried to free the trapped worker.

Firefighters risked their own lives as they used pneumatic bags to force the pipes apart and were eventually able to release the man’s legs.

The road was closed to traffic and residents in the area were evacuated for three hours because of the risk of an explosion as the damage was repaired.

The worker broke his femur but his life was saved by the breathing apparatus he was wearing.

Sheffield Crown Court heard that National Grid Gas Plc, which was supervising the work, failed to comply with its own gas escape procedures and did not undertake a suitable risk assessment.

In addition, the company failed to communicate effectively with the contractors doing the repairs.

As well as a fine of £1m for breaches of the Health and Safety at Work Act, the company was told to pay £26,296 in costs.

Humberside Fire and Rescue Service’s group manager Steve Fraser praised fire crews who carried out the rescue operation.

“The priority when we arrived was the injured man, and getting him out of immediate danger,” he said. “The visibility was virtually zero due to air being dense with gas and dust, and the man had been working 10 feet below ground.

“The crews put themselves in a position which showed courage and bravery of the highest order. They were dealing with gas of an unknown quantity, with potential for another explosion.”

HSE Inspector Ian Redshaw said the incident could easily have resulted in a fatality.

He added: “National Grid Gas failed to follow its own processes and carry out sufficient risk assessments to protect workers and the sub-contractors fixing the leak.”

“This whole incident should act as a stark warning to all those involved in hazardous work – you can have all the written policies in place, but it you do not follow them, if you do not carry out the risk assessments for the task, people could die.”