GLOC
real name: Gareth Lock!
This was posted on the Diving Incident Yahoo Group and I gained permission from the diver to reproduce it on DISMS here https://www.divingincidents.org/incidents/149
In essence, incorrect assembly of Poseidon Mk VI which led to excessive CO2 which was partly detected during pre-breathe but was not recognised as such. Diver lost 'awareness' during descent and was rescued by buddy. Total dive time 3mins, max depth 17m.
Lessons Identified by the Diver
Regards
In essence, incorrect assembly of Poseidon Mk VI which led to excessive CO2 which was partly detected during pre-breathe but was not recognised as such. Diver lost 'awareness' during descent and was rescued by buddy. Total dive time 3mins, max depth 17m.
I assembled the RB the day before the dive and conducted all of the electronic pre-dive tests with the exception of the compulsory pre-dive 5 minute CC pre-breathe. The machine was then shut-down and the battery removed. I was fully compos menti at the time of assembling the RB, however, I was on vacation at the time and may have been relatively more relaxed than usual.
On the following morning of the dive and prior to loading my kit onto the boat, I again conducted all of the electronic tests, followed by the 5 min CC pre-breathe in a seated position. I recall feeling slightly dizzy upon completing the pre-breathe. I commented on this to a highly experienced diver colleague of mine who had accompanied me to the dive site. However, it was early in the morning and I attributed this to simply pre-dive ‘expectation nervousness’, a little of which I normally have prior to any dive.
I then loaded my kit onto the boat and we departed for the dive site. Upon arrival the boat skipper appropriated us into groups according to the intended purpose of our dives. I was paired with two other experienced OC divers with whom I have done many dives in the past. I donned the RB and proceeded to operate it in CC mode. Everything felt normal.
Upon exiting the boat we proceeded to descend. I was slightly shallower, i.e. approximately 2m above, one of the divers with whom I was paired. During the descent I was monitoring my RB’s paddle computer until it indicated that the O2 set-point had changed to 1.0. I recall feeling somewhat odd during the descent. When we were near the bottom the diver below me was oriented with his back to the ground, which I could see approximately 2 m below him, and signalled to me requesting if I was OK. All of a sudden I felt extremely dizzy and in a frank panic state. Hyperventilation immediately set in along with a pounding heart. I recall trying to signal that I was not OK, but did not know how to signal that there was something very wrong with my breathing apparatus. I recall turning to ascend and knowing that I needed to bail out. I do not have a clear recollection of the actual procedure of bailing out to OC, although, given the design of the OC/CC lever on the mouthpiece assembly of this unit I must consciously have done so. The symptoms did not immediately abate and I had to concentrate all of my attention to try to slow down my breathing and to maintain an ascent at a controlled pace. I recall the diver below me coming to my assistance but I do not recall what he did. The onset of the symptoms was exceedingly rapid and I certainly had neither the time nor wherewithal to consider bailing out to my side-slung deco cylinder. I do not recall much of what happened during the ascent.
When we reached the surface I sort of came-to and then removed the mouthpiece from my mouth and proceeded breathing atmospheric air. I recall hyperventilating on surfacing and the symptoms gradually subsiding. Fortunately, the boat was close-by and I was able to rest while holding onto the side of the boat for a few minutes. With the skipper’s help I doffed the gear and climbed onto the boat.
Once in the boat I said to the skipper that we had only descended ‘approximately 3 m and that the whole thing had taken only a fraction of a minute’. I began mentally reciting what I had done during the assembly of the gear to try and understand what had happened. At that point I recalled that I had forgotten to place the inner lid onto the top of the scrubber canister during the assembly of the RB. This was subsequently confirmed when I got home later on. I attributed the symptoms to a ‘CO2 hit’ (acute hypercapnia) in view of the fact that the omission of the internal scrubber lid had resulted in a system in which there was no breathing circuit through the CO2 absorbent.
Lessons Identified by the Diver
1. ‘Confidence breeds carelessness’. Having assembled the RB many times I was not sufficiently fastidious. While I followed a checklist, for some reason I omitted to insert the scrubber lid in the requisite position. I cannot think of any logical reason why I would do this. It is particularly strange since upon arrival at my home the lid was located where all of the other components of the RB are also always located, i.e. it was clearly visible and present at the time at which I was assembling the RB. This behaviour is also out of character for me since I am employed as a scientist and tend to ‘detail obsessiveness’.
2. The 5 minute pre-breathe test can be passed on this unit even if the inner scrubber lid is omitted. While I did feel a little dizzy after the pre-breathe test this did not seem to be a serious problem at the time. It has subsequently been commented by diver colleagues of mine that this might in fact indicate a system design error. This is in view of the fact that the RB circuit may be physically assembled and closed without the lid in place. While the system formally requires the scrubber lid for CC operation there is also no subsequent electronic or other warning of any kind, should it have been omitted.
3. The onset of an acute CO2 hit is extremely rapid and nearly impossible to control. Apparently, all I was able to do was flip the OC/CC lever into the OC position although I have no actual recollection of doing so. I could under no circumstances have bailed out to my off-board cylinder. The onset of hyperventilation, a pounding heart and panic happened literally within a single breath. Hypercapnia also seems to result in short term memory loss since my recollection of the events clearly did not agree with either what was measured by my dive computer or observed by my fellow divers. The diver that assisted me said that I had what looked like a ‘seizure’. Further, the extremely rapid onset of the symptoms might in part be as a result of the increase in gas partial pressure after descending past 10 m depth.
4. I could not have independently controlled my ascent. According to my dive computer our ascent rate reached a maximum of 50m/min. As stated, the ascent was managed by another diver and was not really what I was able to control. It is impossible to say what the ascent would have looked like without his assistance. Had this CO2 hit occurred at the end of a multi-stage deco dive I would likely not be here to recount this story. Such an event would presumably have been an unwanted Xmas gift for my wife.
5. The OC diver that accompanied me did not know how to assist me. This occurred since we did not know with whom we were going to dive prior to the dive and there was insufficient time for me to indicate to the diver how to assist me should something transpire. Fortunately, it seems I had the sense to bail out to my back mounted diluent independently.
6. At the very least, solo RB diving lacks wisdom. The outcome of this incident would likely have been different had I been alone.
Obviously I will not make such a mistake again and I have successfully dived the MK-VI unit subsequently and do intend continuing to dive with RBs. However, being in possession of the knowledge regarding the dangers of CC diving apparently does not prevent them from occurring. Clearly, RB diving requires far greater vigilance than OC diving. It would also seem to me that the idea of ‘recreational’ rebreather diving is oxymoronic.
Regards
Iain
