Jake Molloy, Regional Organiser of the OILC union, told STV on Monday that if reports of gas bubbling up through the water under the platform are true then the situation is likely to be "very volatile".
He said there may be a risk of explosions and of the poisonous gas hydrogen sulphide, although added that the evacuation had been quick and efficient.
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A robot was sent to the scene as police closed the motorway in both directions between Northampton and Milton Keynes.
Mostly dry after a misty start in places
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