In the early hours of November 5, 1983, the semi-submersible drilling rig Byford Dolphin was completing production wells on the North-East Frigg gas field, in the Norwegian sector of the North Sea. Saturation divers working from the rig were being brought back aboard in the diving bell after a shift on the seabed production template, 90 metres below — a routine transfer that ended in the worst diving accident in North Sea history.
Two divers, Bjørn Giæver Bergersen and Truls Hellevik, had just left the bell and entered the first deck decompression chamber; two more, Edwin Coward and Roy Lucas, were resting in the second chamber. The whole system — bell, connecting trunk and chambers — was pressurised to nine atmospheres, and the set procedure required the trunk to be depressurised, and the chamber door closed, before the clamp joining the bell to the chambers could be released.
The clamp was opened while the trunk was still at full pressure and the chamber door stood open. The system explosively decompressed from nine atmospheres to one in a fraction of a second, and the bell was blown clear of the chambers. Coward, Lucas, Bergersen and Hellevik were killed almost instantly. Dive tender William Crammond, working at the clamp, was fatally injured; his fellow tender Martin Saunders survived with serious injuries.
Norway’s expert commission of inquiry (report NOU 1984:11) found that the direct cause was the clamp being released out of sequence — a failure of routines and supervision rather than a mechanical fault in the clamp itself. It never established why, or on whose initiative, the clamp was opened early. The diving system, dating from 1975, had no interlock to make opening under pressure impossible and no pressure gauge outside the chambers; Det Norske Veritas rules adopted in 1982 already required such interlocks, but they were not retroactive, so the rig had never been rebuilt to meet them. The commission also found an “inappropriate burden of work”: in the months before the accident, 38 per cent of bell runs had exceeded the permitted maximum of eight hours, and no shift plan or record of divers’ hours was kept.
Within a month of the accident, Det Norske Veritas and the Norwegian Petroleum Directorate made safety interlocks an absolute requirement on every bell and chamber system, and shift plans, tighter bell-run limits and overtime controls for divers followed. In 2009, twenty-six years after the accident, the Norwegian government paid compensation to the divers’ families.