One of two men who died in a disused fuel tank had called emergency services for help on his mobile phone before climbing into the tank.
Crews worked late into the night to retrieve the bodies
The welders have been identified as Brian Dove, 55, of Butt Lane, Burgh Castle, Norfolk, and his stepson, Charles Buckenham, 52, of Hardy Close in Lowestoft, Suffolk.
They had been dead for a number of hours by the time emergency services managed to reach them on Wednesday night.
The men were working for the marine engineers Small and Co at Lake Lothing, Oulton Broad in Suffolk.
It is thought one man went into the tank to look at it, but did not come out.
Investigation under way
The second man called for an ambulance before going inside himself at about 1430 GMT on Wednesday.
A spokesman for the East Anglian Ambulance Service said they were already too late when they arrived at the quayside at Lake Lothing.
It took emergency services seven hours to retrieve their bodies.
The search of the five meter by 15 meter tank was hampered by water and slurry.
Suffolk Police said they were treating the deaths as an industrial accident.
A Health and Safety Executive investigation has begun into the accident.