Gas explosion risk at stricken North Sea rig Total's Elgin platform in 2009. The French energy giant has resorted to a mini-submarine ...

Gas explosion risk at stricken North Sea rig

Total's Elgin platform in 2009. The French energy giant has resorted to a mini-submarine in an increasingly desperate bid to plug a huge gas leak at a North Sea rig but played down fears of a massive explosion. (AFP Photo)

French energy giant Total resorted to a mini-submarine Wednesday in an increasingly desperate bid to plug a huge gas leak at a North Sea rig but played down fears of a massive explosion.

An expert warned that gas pouring from the Elgin platform could ignite with catastrophic consequences if it came into contact with a flare left burning when 238 workers were evacuated from the rig on Sunday.

But a Total spokeswoman said the wind was not currently blowing the cloud of highly flammable gas towards the flare on the rig, which lies 150 miles (241 kilometres) off the coast of eastern Scotland.

"We don't see it as a risk because of the prevailing winds and the location of the flame in relation to where the gas leak is," the spokeswoman said.

Total called in an exploration ship carrying the remote-controlled minisub late Tuesday in an effort to assess the underwater leak, it said.

The ship, the Highland Fortress, was standing by Wednesday outside a two-nautical mile (3.7 kilometres) exclusion zone around the platform.

There is a risk meantime that if the wind currently blowing the gas away from the flare dropped, the gas could ignite, said Simon Boxall, an oceanographer at Southampton University in southeast England.

"The chances are the gas will disperse quite quickly," Boxall told AFP. "But if the wind stops completely, gas will build up towards the flame. This could create an explosion.

"At the moment things are working on the side of Total," he added. "The flare is at the highest part of the rig, and the gas itself... is fairly heavy, so it's lying low."

Total says the leak is the most serious problem it has faced in the North Sea for a decade.

The company said it was considering various ways of stopping the leak, but admitted it could take six months to dig a relief well to stop the flow of gas.

"There has been some speculation about a second well being drilled," a spokesman said.

"But we believe it could take up to six months if that was the preferred option," he added.

The company's shares, which plunged 6.0 percent on the French stock exchange on Tuesday, were down a further 1.0 percent to just over 38 euros in early trading on Wednesday.

Total's UK safety manager David Hainsworth said the company expected the weather to stay in its favour in the coming days.

"The weather forecast is such that the wind direction remains the same for the following five to six days, and we're evaluating options to extinguish this flare," he told BBC television late Tuesday.

Flares on offshore platforms are commonly used to burn off excess gas that the rig does not use or capture, but it was not clear whether Total had left the flame burning intentionally when the platform was abandoned.

More than 300 people have been evacuated from two rigs since the leak was discovered on Sunday and a six-mile long sheen of gas condensate has spread on the water nearby.

Shell has shut down production at its Shearwater platform and Noble Hans Deul rig four miles away and evacuated 85 crew as a precautionary measure.

The last major accident in the North Sea was in 1988, when the Piper Alpha oil platform, operated by the US-based Occidental Petroleum, exploded killing 167 people.

The incident comes two years after BP's reputation was badly hit by a blowout at the Deepwater Horizon oil drilling rig in the Gulf of Mexico.

The explosion killed 11 crewmen and caused oil to gush into the water triggering the worst environmental disaster in US history.

(Agencies)