Surface decompression near-miss

What happened?

During surface decompression, following a SURDO2 42msw/40min dive, the depth of the chamber was unintentionally decreased from 12msw to 5msw forty minutes into the decompression. Immediately after this was discovered,  Treatment Table 5 was initiated. The divers did not present any symptoms before, during or after the incident.

What was the cause?

Investigation concluded that the two main causes of the failure were:

• The exhaust valve was not completely closed; no technical faults on the system;
• The dive supervisor running the decompression was teaching new divers chamber operation and got distracted. Under local regulations applicable in this incident, it is the supervisor who is responsible for running the chamber.

Corrective action/lessons learned:

• The root cause was the dive supervisor running the decompression, without anyone supervising him (no human second barrier);
• Procedures/manuals were updated to highlight that a diver runs the chamber during decompression, and the dive supervisor controls the diver;
• The chamber panel was modified with a visual and non-mutable alarm for the venting;
• A visual alarm showing depth shallower than 12msw, and an additional camera for the SUPV to see the DDC chamber readings was installed.

Members may wish to refer to:                 

• Dive bell gas loss during internal bell checks
• Uncontrolled decompression of diving bell   
• Diver experienced an air flow restriction
• Learning outcomes from a real time diver recovery