An investigation is under way into the deaths of two workers following a sudden escape of gas on board an oil production platform in the North Sea.
An investigation team has been sent to the Brent Bravo
The incident happened on Thursday afternoon when there was a release of gas on the Brent Bravo platform, 116 miles north-east of Lerwick, Shetland.
The two men have been named as Sean McCue, 22, of Kennoway in Fife, and Keith Moncrieff, 45, of Invergowrie, Tayside.
Unions have raised new concerns about a backlog of maintenance on the Brent Bravo but Shell said the Health and Safety Executive had given the a clean bill of health to its operations.
About 60 other non-essential platform workers were evacuated to the nearby Brent Alpha and Brent Charlie platforms so that the build-up of gas could be dealt with.
A doctor, who was flown from a nearby platform, pronounced the men dead at the scene.
A coastguard spokesman said the bodies were expected to remain on the platform until later on Friday.
Shell Expro Managing Director Tom Botts said the emergency response system immediately shut the platform down.
"We knew that the men were still in the leg and sent a rescue team to help them once the gas had been cleared.
"The gas in the leg was quickly and safely evacuated, a rescue team then entered the leg and recovered both men who were immediately seen by the doctor but had no vital signs.
"We are deeply saddened by the deaths of two of our colleagues. Our thoughts are with their families and friends and we will do all that we can to ensure that they are supported through this difficult time."
An investigation team made up of five police officers, Shell investigators and staff from the Health and Safety Executive (HSE) is on the platform to determine the cause of the accident.
Jake Molloy, of the offshore union OILC, said unions had already complained to the HSE about a backlog of maintenance and staffing issues in the Brent Field, particularly on the Brent Bravo platform.
Last month the company defended the level of safety after 20 workers' safety representatives resigned in a dispute over negotiations on the new European working time regulations.
Most of those who resigned were from the Brent Field, but Mr Botts dismissed suggestions the events were related.
"We had a full audit and review by the Health and Safety Executive not only of the Brent Field but of all of our operations in the North Sea and they have come back with a very robust stamp of approval on our operations," he said.
But Mr Molloy said he felt there could be a connection with concerns raised over pipes which leak and are then patched.
"The suggestion from the workforce that these lads had gone down to inspect a leak or a patch suggests to me that it is related to the concerns we raised earlier in the year," he said.
In April, he said, his own union and Amicus had raised a complaint with the HSE over maintenance backlogs, manning levels and other issues.
"That investigation went on for three months and there are several outstanding items which Shell have yet to address," Mr Molloy added.
But Taf Powell, director of HSE's offshore division, said there was no evidence the existing concerns are related to the deaths.
"We wrote to Shell last month setting out nine concerns and we've given them 30 days to reply.
"That deadline isn't up yet but I do expect a very full reply and response from Shell and remedial action from them.
"The issues that we investigated revealed no imminent risks to the instillation - we've taken no enforcement action."
Shell said it would probably be weeks before the full circumstances behind the deaths were known.
The Brent Bravo is one of four oil production and storage platforms in the UK northern sector of the North Sea that make up the Brent field.
Two of its legs are flooded with sea water. The third, the utility shaft, contains process equipment and allows access to the top of the storage cells.