Incident Report

2025-07-04Diver is a recently certified DiveRite Choptima (O2ptima) rebreather diver and was using Vobster Quay as a training ground building up hours on the unit prior to taking it into overhead environments. Dive was planned for the Friday and the unit was built up following the manufacturers checklist on the Thursday evening in a relaxed environment with no distractions. No issues with the unit were detected during that build process with leak down, positive and negative tests all behaving as expected. Diver travelled from Gloucestershire -> Vobsters with the Choptima safely secured upright on the rear seat of the car. On arrival, diver moved Choptima from vehicle to one of the "kit up benches" and commenced the "pre-jump" checklist for the unit: * Diver pulled a negative pressure test. No issues were detected. * Diver attempted a positive pressure test and the unit immediately collapsed (lungs visibly shrinking) Inspection of the unit identified the left hand (inhalation) tower of the scrubber canister had partially backed out exposing a glimpse of the sealing o-ring. Negative pressure check pulled the tower back onto the canister effecting a seal, but the positive pressure was enough to compromise the o-rings function. It appeared that transporting the unit in that orientation/placement in the vehicle was enough to cause the tower to "back out" Diver was able to re-tighten the tower by hand, resolving the issues and allowing the diver to build more confidence in their ability to use the unit in more arduous conditions. Pre-jump checks are there for a purpose. The CDG pre-jump checklist recommends the checks are performed with the unit "on-diver prior to entering water" (https://cavedivinggroup.org.uk/download/immediate-pre-dive-rebreather-checks/?wpdmdl=6942&ind=1585904794460), in this case the diver was safely at the bench in street clothing and not standing waist deep in water with a potentially compromised scrubber canister. The diver was very aware that pre-jump checks are specified by manufacturer in a specific order for good reason. Whilst there may be a temptation to rush / skip specific checks, an observation that took literal seconds was enough to prevent this diver entering the water with a potentially life altering equipment configuration. Whilst this was trivial to resolve with barehands in a nice clean environment, resolving in a muddy cave environment may have resulted in an aborted dive. Diver to work with more experienced operators to determine suitable additional tooling to be brought to an underground dive base.