The gas explosion killed a family of four

Andrew Hepburn, 31, said he stopped the gas supply to houses in Larkhall after an explosion which killed the Findlay family in 1999.

Despite operating the "slam shut" system, heavy concentrations of gas remained in the area.

Transco has pleaded not guilty to breaching health and safety laws.

Andrew and Janette Findlay, Stacey, 13, and Daryl, 11, from Larkhall, South Lanarkshire, died in the explosion on 22 December, 1999.

Mr Hepburn told the High Court in Edinburgh that when he arrived at the scene of the blast, he found number 42 Carlisle Road completely destroyed.

Area evacuated

A fire brigade officer drew his attention to a gas governor on the garden wall on number 42.

Mr Hepburn explained to the jury that the governor or regulator was used to reduce the gas supply from the medium pressure main to low pressure to serve the houses.

Despite operating the "slam shut" system, gas fires were still burning, he said.

Asked by advocate depute Frank Mulholland what was fuelling the fires, Mr Hepburn replied: "Gas coming up from under the ground."

Mr Hepburn said he then began to monitor the properties for any concentrations of gas in the air.

His first reading at the front of what had been 42 was 100% gas and next door at 40 the reading was 75%.

Mr Hepburn told the court that at 1115 GMT he had called for the evacuation of the area as he was still getting high readings of gas, that he considered dangerous.

'No difference'

Mr Mulholland said: "But you had shut the slam shut".

"It made no difference" said Mr Hepburn.

The allegations against Transco centre on the firm's maintenance, repair and record keeping procedures, particularly related to its ductile iron piping.

It is alleged that a section of the main at Larkhall was corroded and was leaking.

It is also alleged that on 22 December, 1999 quantities of gas escaped from the main, entered the foundations of the house and formed a gas cloud which ignited and exploded.

The trial continues.