The Byford Dolphin is a semi-submersible drilling rig operated by Dolphin Drilling, a Fred. Olsen Energy subsidiary. The drilling rig is an “Aker H-3” design which was built in 1974. It is able to maneuver with its own engines (to counter drift and ocean currents), but for long-distance relocation it must be moved by specialist tugboats.As a drilling rig, the Byford Dolphin is equipped with advanced drilling equipment and has to meet strict levels of certification under Norwegian law. However, the rig has suffered some serious accidents, most notably an explosive decompression accident in 1983 known as the Byford Dolphin diving bell accident that killed five workers and badly injured one.Diving Bell AccidentAt 4:00 a.m. on 5 November 1983, four divers were in a decompression chamber system attached by a trunk (a short passage) to a diving bell on the rig, being assisted by two dive tenders. One diver was about to close the door between the chamber system and the trunk when the chamber was explosively decompressed from a pressure of nine atmospheres to one in a fraction of a second. Five of the men were killed; the other was severely injured.The situation just before this accident was: Decompression chambers 1 and 2 were connected via a trunk to a diving bell. This connection was sealed by a clamp operated by two tenders, who were themselves experienced divers. A third chamber was connected to this system, but was not involved. On this day, divers D1 (35 years old) and D2 (38 years old) were resting in chamber 2 at a pressure of 9 atm. The diving bell with divers D3 (29 years old) and D4 (34 years old) had just been winched up after a dive and joined to the trunk. Leaving their wet gear in the trunk, the divers then climbed through the trunk into chamber 1.The normal procedure would have been:1) close the bell door2) the diving supervisor would then slightly increase the bell pressure to seal this door tightly3) close the door between the trunk and chamber 14) slowly depressurize the trunk to 1 atmosphere5) open the clamp to separate the bell from the chamber system.The first two steps had been completed and D4 was about to carry out step 3) when, for some reason, one of the tenders opened the clamp which resulted in explosive decompression of the chamber. A tremendous blast shot from the chamber through the trunk, pushing the bell away and hitting the two tenders. The tender who opened the clamp died, and the other was severely injured.Diver D4 was shot out through the small jammed hatch door opening, and was ripped apart. Subsequent investigation by forensic pathologists determined D4, being exposed to the highest pressure gradient, violently exploded due to the rapid and massive expansion of internal gases. All of his thoracic and abdominal organs, and even his thoracic spine were ejected, as were all of his limbs. Simultaneously, his remains were expelled through the narrow trunk opening left by the jammed chamber door, less than 60 centimeters (24 inches) in diameter. Fragments of his body were found scattered about the rig. One part was even found lying on the rig’s derrick, 10 meters (30 feet) directly above the chambers. His death was most likely instantaneous and painless.Medical FindingsMedical investigations were carried out on the four divers’ remains. The most conspicuous finding of the autopsy was large amounts of fat in large arteries and veins and in the cardiac chambers, as well as intravascular fat in organs, especially the liver. This fat was unlikely to be embolic, but must have “dropped out” of the blood in situ. It is suggested the boiling of the blood denatured the lipoprotein complexes, rendering the lipids insoluble.The rigor mortis was unusually strong. The hypostases (accumulations of blood in internal organs) were light red, and in two cases, there were numerous hemorrhages in the livers. All the organs showed large amounts of gas in the blood vessels, and scattered hemorrhages were found in soft tissues. One of the divers had a large sub-conjunctival bulla (a blister in the tissue of the eye).InvestigationThe committee investigating the accident concluded it was due to human error on the part of the dive tender who opened the clamp. It is not clear whether the tender who opened the clamp before the trunk was depressurized did so by order of his supervisor, on his own initiative, or because of miscommunication. At the time, the only communication the tenders on the outside of the chamber system had was through a bullhorn attached to the wall surface; with heavy noise from the rig and sea, it was hard to listen in on what was going on. Fatigue from many hard hours of work also took its toll amongst the divers, who often worked 16-hour shifts. Modifications to the "planned use of overtime" policies were made as a result of further investigation into this incident.This incident was also an engineering failure, because the obsolete Byford Dolphin diving system from 1975, was not equipped with fail-safe hatches, outboard pressure gauges and an interlocking mechanism, which would prevent the trunk from being opened while the system was under pressure. A law had been passed in Norway by Norske Veritas, prior to the accident in 1982, with the following regulation: "Connecting mechanisms between bell and chambers are to be so arranged that they cannot be operated when the trunk is pressurized", therefore requiring such systems to have fail-safe seals and interlocking mechanisms. One month after the accident, Norske Veritas and the Norwegian oil directorate made the law final for all bell systems.Among others including written publications, former crew members of the Byford Dolphin and NOPEF (Norwegian oil and petro-chemical union) have come forward and claimed the investigation was a cover-up. They claimed that the commission investigating the accident did not mention the irresponsible dispensations requested by Comex and authorized by the diving section to the Norwegian Petroleum Directorate, on vital equipment in their report, which played a vital role in the accident's occurrence. They also alleged the accident was due to a lack of proper equipment, including clamping mechanisms equipped with interlocking mechanism (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.Post InvestigationThe conclusions of the investigation were disputed and a group of divers gathered evidence with the intention of "find[ing] justice for all of the crew of the Byford Dolphin." The group formed the "North Sea Divers Alliance" in the early 1990s and now campaigns for compensation for divers killed or injured in the Norwegian Sector of the North Sea.Subsequent LawsuitThe North Sea Divers Alliance, formed by early North Sea divers and the relatives of those killed, continued to press for further investigation, and in February 2008 obtained a report that indicated the real cause was faulty equipment. Clare Lucas, daughter of Roy Lucas, said: "I would go so far as to say that the Norwegian Government murdered my father because they knew that they were diving with an unsafe decompression chamber." The families of the divers eventually received damages from the Norwegian government, 26 years after the tragedy.Other IncidentsIn late November 2001, the rig was left adrift without control in a storm. Although 17 of the 71 workers were evacuated by helicopter, the company claimed there was no serious danger.On 17 April 2002, a 44 year old Norwegian worker on the rig was struck on the head and killed in an industrial accident. The accident resulted in the Byford Dolphin losing an exploration contract with Statoil, who expressed concerns with the rig’s operating procedures. The incident cost the company millions of dollars in lost income.