Incident Report

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Incident Report 2020-05-01T16:26:00+00:00

Poseidon Cyklon 300 Exhaust Circlip

Incident Date


Incident Description

In 1979 after re-assembling the exhaust section of a Poseidon Cyklon 300 the diver did not fit the circlip that retains the exhaust housing. Subsequently when diving the end of the second stage fell off and the air supply failed catastrophically.

Lessons Learned

One option is to ensure that this circlip is properly fitted. It should be noted that some divers deliberately remove this circlip permanently because it then allows them access to the exhaust diaphragm without any tools so that any blockage of the diaphragm can be cleared. Blockage of the diaphragm by gravel entering an unused second stage through the mouthpiece is a known failure mode. Where the circlip is removed the cable tie that secures the mouthpiece is fixed in such a way that the locking section is adjacent to the exhaust housing and about 10mm to 20mm of spare tie is left in place. This tail then presses against the housing to keep it in place. There is some doubt as to the practicalities of actually effecting the housing removal and exhaust clearance underwater with gloves on hence an alternative approach is to retain the circlip. Note the ingress of small gravel can be prevented by fixing a fine gauze or stocking across the mouthpiece.
Line Management Negligible
Gas Management Negligible
Equipment Management Major
Equipment Failure Negligible
Training Negligible
Medical Negligible
Planning Negligible
Procedural Error Negligible
Cave Environment Negligible
Weather Negligible
Other Factor Unknown