Diving Bell Accident

“On this day in 1983, the North Sea drilling rig known as Byford Dolphin suffered an explosive decompression, killing five workers and injuring one. It was one of the most serious diving accidents in history and has led to a series of new diving regulations.

Byford Dolphin is a semi-submersible drilling rig currently contracted out by British Petroleum. The rig is some 110 metres long, 67 metres wide, and 36 metres deep, and can drill at depths of 6,000 metres. In the early morning hours of 5 November 1983, a team of four divers was working in the Frigg gas field in the North Sea. Two divers in a diving bell, a chamber used to take people to the depths of the ocean, had just been cranked up to the surface. They were crawling through a passageway known as a trunk, to an attached, sealed decompression chamber. A similar nearby chamber held two more of their diving team. Each of these chambers–the diving bell, the trunk, and decompression chambers–were carefully pressurised and a minor accident could dramatically, and potentially fatally, change the air pressure. The divers had closed the diving bell door and were about to close the door between the trunk passageway and their chamber, when an outside assistant mistakenly opened the diving bell clamp. The chamber which the two divers had just entered decompressed from a pressure of nine atmospheres to one atmosphere in a fraction of a second, producing a tremendous blast. The explosive decompression killed all four of the divers in the two chambers and the dive tender, or outside assistant, who had mistakenly opened the critical clamp.

After an investigation, the accident committee concluded the explosion was due to human error on the part of the dive tender who accidentally opened the diving bell clamp. Whether it was fatigue, miscommunication, or an error made by the tender’s supervisor, it is not clear why the dive tender opened the clamp before the trunk was depressurised.

After the findings were released, former crewmembers of the Byford Dolphin and Norwegian oil and petro-chemical union NOPEF called the investigation a cover-up and attributed the accident to outdated equipment and engineering failures. Dating to 1975, the obsolete diving system on the Byford Dolphin rig was not equipped with fail-safe hatches, outboard pressure gauges, or interlocking mechanisms that would have prevented the trunk from being opened when it was. Some years later an alliance of North Sea divers and the relatives of those killed in the Byford Dolphin accident, obtained a report that indicated that the real cause of the explosion was faulty equipment.

The Norwegian oil directorate and its regulations body, Norske Veritas, have since adopted many new safety features for drilling rigs and their diving systems, including a law that mandates chamber doors and clamps are built such that they cannot be opened when the trunk is pressurised.”