Trapped pressure release incident
- Safety Flash
- Published on 22 June 2006
- Generated on 14 September 2026
- IMCA SF 08/06
- 2 minute read
A Member has reported a trapped pressure release incident in a dive system transfer chamber.
What happened?
The incident occurred onboard a diving support vessel undergoing commissioning of its saturation diving system following a dry dock. The system was compressed to an equivalent internal depth of 333 msw and then returned to ambient surface pressure.
A saturation diver entered the dive system transfer chamber, less than an hour after the system had been returned to surface pressure, and decided to flush the toilet system as there was a strong smell of sewage. On operating the bulkhead valve to evacuate the holding cylinder no movement of the contents was heard, so the diver assumed that there was no pressure in the system and opened the ball valve next to the WC. In doing so he inadvertently operated the valves out of sequence. The external ball valve had not been checked and was in the closed position. Trapped pressure inside the holding cylinder was then released into the chamber via the WC, back-flushing the contents of the holding cylinder – raw sewage – into the chamber with it, covering the diver. The force of the trapped pressure, which could have been as much as 30 bar, was sufficient to lift the toilet seat and fracture it.
The diver – following a shower and change of clothes – visited the medic, who confirmed no medical action was required.
IMCA Safety Flashes summarise key safety matters and incidents, allowing lessons to be more easily learnt for the benefit of the entire offshore industry.
The effectiveness of the IMCA Safety Flash system depends on the industry sharing information and so avoiding repeat incidents. Incidents are classified according to IOGP's Life Saving Rules.
All information is anonymised or sanitised, as appropriate, and warnings for graphic content included where possible.
IMCA makes every effort to ensure both the accuracy and reliability of the information shared, but is not be liable for any guidance and/or recommendation and/or statement herein contained.
The information contained in this document does not fulfil or replace any individual's or Member's legal, regulatory or other duties or obligations in respect of their operations. Individuals and Members remain solely responsible for the safe, lawful and proper conduct of their operations.
Share your safety incidents with IMCA online. Sign-up to receive Safety Flashes straight to your email.