Partial pressure of oxygen (PPO₂) getting low in bell
- Safety Flash
- Published on 28 May 2019
- Generated on 16 October 2025
- IMCA SF 12/19
- 2 minute read
During saturation diving at approximately 147 msw, the diving supervisor noticed that Partial Pressure of Oxygen (PPO₂) was getting low in the diving bell.
What happened?
The supervisor instructed the bell man to inject some oxygen into the bell.
The bellman opened the main valve which charges a smaller bottle (buffer tank) with oxygen. He then closed the main valve and opened the second valve which allows the dosage of oxygen to enter the bell. A few minutes later, he observed that the main bottle was empty. He secured the valves and notified the supervisor.
The supervisor began to purge the bell with saturation breathing mix and instructed the bellman to put on a built-in breathing system (BIBS) mask. A few minutes later, the supervisor instructed the diver to return to the bell, remove his helmet and put on a BIBS. The bell was recovered to the surface.
Once brought to the surface, the entire oxygen set up was checked for leaks, and operational status. There were no issues found with the equipment.
location of panel
valve set-up
new panel
close-up of valve
Our Member's findings
- Bell O₂ make-up was routinely performed by bell divers.
- The oxygen panel was inconveniently located behind the diver #2 umbilical.
- The panel was capable of opening both valves at once, allowing the buffer bottle to be introduced into the bell, and into the main O₂ supply.
What actions were taken?
- Bell O₂ make up performed by life support technician (LST) by flushing with premix instead of bell divers adding O₂.
- Tubing was added to redirect Bell O₂ to near the saturation bell scrubber fan.
- The oxygen panel was moved 45 cm from the old position, re-installed and the divers were given instruction on its operation.
- The new valve configuration – a sliding mechanism and the tight tolerance if the valve is opened – will remove the likelihood that both valves could be open at the same time.
- The buffer tank was changed from a single penetration to a double penetration, with valves top and bottom in lieu of a single in/out valve.
Related Safety Flashes
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IMCA SF 01/16
7 January 2016
-
IMCA SF 06/12
25 June 2012
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