Byford Dolphin was registered in Hamilton, Bermuda,[1] and drilled seasonally for various companies in the British, Danish, and Norwegian sectors of the North Sea.

Byford Dolphin was able to maneuver with its own engines (to counter drift and ocean currents), but for long-distance relocation it had to be moved by specialized tugboats.

[4] The normal procedure would have been: The first two steps had been completed when a mechanical failure caused the clamp that was keeping the trunk sealed to open before Hellevik (diver 4) had closed the door to the chamber.

Air rushed out of the chamber system with tremendous force, jamming the interior trunk door and pushing the bell away, striking the two tenders.

With the escaping air and pressure, gross dismemberment ensued; it included bisection of his thoracoabdominal cavity, which resulted in fragmentation of his body, followed by expulsion of all of the internal organs of his chest and abdomen, except the trachea and a section of small intestine, and of the thoracic spine.

At the time, the only communication the tenders on the outside of the chamber system had was through a megaphone attached to the wall surface; with heavy noise from the rig and sea, it was hard to listen in on what was going on.

One month after the accident, Norske Veritas and the Norwegian oil directorate made the rule final for all bell systems.

[citation needed] Among others, former crew members of Byford Dolphin and NOPEF (a Norwegian oil and petro-chemical union) have come forward and claimed the investigation was a cover-up.

They also alleged the accident was due to a lack of proper equipment, including clamping mechanisms equipped with interlocking mechanisms (which would be impossible to open while the chamber system was still under pressure), outboard pressure gauges, and a safe communication system, all of which had been held back because of dispensations by the Norwegian Petroleum Directorate.

The accident resulted in Byford Dolphin losing an exploration contract with Statoil, which expressed concerns with the rig's operating procedures.