en.wikipedia.org/wiki/Byford_Dolphin
As a drilling rig, the Byford Dolphin is near the top of its class. It is equipped with advanced drilling equipment and has to meet very high levels of certification under Norwegian law.
This connection was sealed by a clamp operated by two tenders (T1 and T2), who themselves were 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.
Leaving their wet gear in the trunk, the divers then climbed through the trunk into chamber 1 The normal procedure would have been as follows: close the bell door, the diving supervisor would then slightly increase the bell pressure to seal this door tightly, close the door between the trunk and chamber 1, slowly depressurize the trunk to 1 atm, and open the clamp to separate the bell from the chamber system. Operations and had been completed and D4 was about to carry out operation when, for some reason, one of the tenders opened the clamp.
A tremendous blast shot from the chambers 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.
edit Investigation The committee investigating the accident concluded that 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 or on his own initiative, due to miscommunication.
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 on awareness amongst the divers, who would often work 16-hour shifts.
cover-up, as the commission investigating the accident did not mention the irresponsible dispensations on vital equipment in their report, which had a large role in the accidents occurrence, and that 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 safe communication system, which had been held back due to dispensations done by the Norwegian Petroleum Directorate.
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