Keith Moncrieff and Sean McCue had been working on a utility leg

The deaths of two oil workers on board a North Sea platform were "entirely avoidable", an inquiry has heard.

A fatal accident inquiry (FAI) was told that a series of failures by oil giant Shell had led to Keith Moncrieff and Sean McCue losing their lives.

The pair were overcome by a massive gas escape while inspecting a repair on the company's Brent Bravo platform in 2003.

The FAI, which began at Aberdeen Sheriff Court last October, was ordered by Lord Advocate Colin Boyd.

Mr Moncrieff, 45, of Invergowrie, near Dundee, and 22-year-old Mr McCue, of Kennoway in Fife, died on a utility leg of the platform on 11 September.

The oil firm Shell was fined £900,000 following their deaths.

'Flawed thinking'

During closing submissions on Monday, Ernest Barbour, procurator fiscal, said: "The deaths on the Brent Bravo of Sean McCue and Keith Moncrieff could and should have been avoided.

"The tragic events that occurred were entirely avoidable."

He added that this was due to Shell's failures to follow certain procedures and "fundamentally flawed thinking" in the system being used.

The inquiry had earlier heard that a temporary patch had been placed on the leaking pipe nearly a year before the incident on the platform.

When Mr Moncrieff and Mr McCue went to inspect it, a broken valve led to the release of up to 2.5 tonnes of gas.

"This whole tragedy may have been avoided if the patch had been replaced earlier," said Mr Barbour.

There is a substantial body of evidence that Mr Moncrieff viewed the work he was to carry out as involving the replacement of a patch   Stuart Gale QC Representing Shell

Mr Barbour said when Mr Moncrieff and Mr McCue went to inspect the patch, the platform had been started up, despite there being knowledge that a number of valves were not operating properly.

Sheriff Colin Harris also heard that since the Brent Bravo deaths there had been changes and improvements in Shell's operating procedures.

This included clear and thorough risk assessments being carried out before beginning work on a hydrocarbon or safety critical line and discouraging any delay in maintenance work.

Stuart Gale QC, representing Shell, told the inquiry the patch placed on the pipe in November 2002 was seen purely as a temporary measure.

He said measures were put in place to deal with the repair and that it was expected an onshore surveyor would travel to the rig to inspect the pipe.

No explanation

He added that for "reasons that are unclear" the patch stayed in situ until September 2003.

"That it did remain in situ is a matter of regret for Shell and one for which it cannot offer a satisfactory explanation," he said.

The inquiry heard a number of employees on the platform had given evidence that Mr Moncrieff and Mr McCue had been asked to go and inspect the temporary repair on 11 September but had not at any stage been told to replace or try and fix it.

Mr Gale said another worker had seen Mr Moncrieff before he went to look at the patch with items used for replacing a patch, including a screwdriver.

"There is a substantial body of evidence that Mr Moncrieff viewed the work he was to carry out as involving the replacement of a patch," he said.

"Such work clearly required a work permit if it was to be properly carried out due to the procedures in place."