The incident happened at the Royal Stoke University Hospital in January 2014 during work to create a new car park and install new drains.

An excavator struck a buried plastic gas pipe causing significant damage and a large release of gas.

The hospital declared a major incident and set up an exclusion zone around the pipe causing traffic chaos on surrounding roads.

Stafford Magistrates’ Court heard that the pipe fed an energy centre that provided 90% of the hospital’s heating.

Fortunately, the energy centre was duel fuel and engineers were able to quickly switch the heating supply to oil.

It took 90 minutes to stop the leak, during which time a significant quantity of gas was released into the atmosphere.

An HSE investigation found that O’Rourke had failed to implement a safe system of work and follow relevant guidance for safe digging when dealing with buried underground services.

HSE guidance states that the position of plastic (PE) gas pipes should be located by hand digging before mechanical excavation begins.

It also states that mechanical excavators should not be used within 500mm of a buried gas pipe.

Laing O’Rourke Construction Ltd, of  Dartford, Kent, was fined £14,000 and ordered to pay costs of £1,723 after pleading guilty to breaching CDM regulation.

Speaking after the hearing, HSE inspector Andrew Bowker said: “As a large, experienced construction company, Laing O’Rourke were well aware of the relevant guidance on dealing with underground services.

“On this occasion there was a general breakdown in the company’s comprehensive health and safety procedures for preventing such an incident.

“It failed to suitably plan and monitor the work; failed to hand dig trial holes to locate a known gas pipe; failed to have a suitable exclusion zone between the excavator and the pipe; and failed to use safe digging methods to expose the pipe.

“The result was a highly dangerous situation that had the potential to expose construction workers, hospital staff, patients and visitors to an initial explosion and subsequent fire.”