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Diving bell accident On 5 November 1983 at 4:00 a.m., while drilling in the Frigg gas field in the Norwegian sector of the North Sea, 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. The four divers were

Edwin Coward (British, 35 years old) Roy Lucas (British, 38 years old) Bjørn Giæver Bergersen (Norwegian, 29 years old) Truls Hellevik (Norwegian, 34 years old)[10] Hellevik was about to close the door between the chamber system and the trunk when the chamber explosively decompressed from a pressure of nine atmospheres to one atmosphere in a fraction of a second. One of the tenders, 32-year-old William Crammond of Great Britain, and all four of the divers were killed instantly; the other tender, Saunders, was severely injured.[10]

The normal procedure would have been

1. 
   

   Close the bell door.

   
   


2. 
   

   The diving supervisor would then slightly increase the bell pressure to seal this door tightly.

   
   


3. 
   

   Close the door between the trunk and chamber 1.

   
   


4. 
   

   Slowly depressurize the trunk to 1 atmosphere.

   
   


5. 
   

   Open the clamp to separate the bell from the chamber system.

   
   

The first two steps had been completed when, for an unknown reason, one of the tenders (Crammond) opened the clamp before Diver 4 (Hellevik) could close the door to the chamber. This resulted in the explosive decompression of the unsealed chamber. Air rushed out of the chamber with tremendous force, jamming the interior trunk door and pushing the bell away, striking the two tenders. The tender who opened the clamp was killed while the other was severely injured.

Coward, Lucas, and Bergersen were exposed to the effects of explosive decompression and died. Subsequent investigation by forensic pathologists determined Hellevik, being exposed to the highest pressure gradient and in the process of moving to secure the inner door, was forced through the 60 centimetres (24 in) in diameter opening created by the jammed interior trunk door by escaping air and violently dismembered, including bisection of the thoracoabdominal cavity which further resulted in expulsion of all internal organs of the chest and abdomen except the trachea and a section of small intestine and of the thoracic spine and projecting them some distance, one section later being found 10 metres (30 ft) vertically above the exterior pressure door.

There was a differential pressure of 9 atmospheres, or roughly 132psi. The 24in diameter opening would have an area 452 square inches, so anything blocking that would be exposed to a force of up to approximately 25 tonnes by the air trying to escape. There is a picture on the internet of the remains of Hellevik, and it's not nice.