Quote:
| Originally Posted by Neil McLeod Now, I am reporting this experience for two reasons: firstly because I was complacent and checked my unit before I loaded it on to a boat and not immediately predive (something I will not be repeating); and secondly because I feel it demonstrates what excellent units these are. I presently dive a Dolphin with an Oxy2 which relays PPO2 to an Aladin Oxy X.
Yesterday I assembled the unit, checked flow from dosage unit and did pressure tests. All was well. The unit was then placed on the RHIB and secured with bungie to the bottlerack. The seas were fairly calm but the unit was still moving back and forward a little with each wave.
At the dive site we tied off to the permanent bouy at slack water and I and the others got into our gear - everyone else was on open circuit. "Gas, gauge, gag" and a three minute prebreath. All seemed fine. Rolled in when told to and went to the line. Everyone happy so down we went. As we descended two things struck me as abnormal. There was a slightly increased inspiratory effort and as I descended the unit continued to sound noisy. It was still breathing easily enough and I was adding air normally to maintain neutral bouyancy. The FiO2 in the loop was higher than I would have expected. I checked my gauge and I had used 40 bar on the descent! I was now at 25 meters. I checked the valve was clicked down and nothing changed, still noisy exhalations. Reckoned I had a serious leak. I briefly considered going to bale out, but still had plently of O2 rich gas and was still able to breath it easily. As was effectively on open circuit signaled to buddy and started slow accent, relaxed 3 minute stop at 5m then slowly to surface with over 100 bar left (4 litre bottle).
Back in the boat opened the unit and found that the p-connector between the expiratory bag and the scrubber had come loose. The scrubber was mostly flooded. Now this I found strangely reassuring and a testiment to the design of these units. With such a major leak the bags cannot be distended instead they are flattened and depend on the lengths of spiral wrap to maintain a channel. The bags then work as flap valves and the second stage demand valve kicks in. Expired air is directed to the expiratory limb and then exhausted via the leak. The construction of the housing is such that you cannot fully slide the outer collar of the p-connector off the scrubber and this again limits the ingress of water.
Points:
Up to now have checked unit prior to loading and assumed that nothing came adrift on journey out to dive sites - will not assume this in future.
If something just doesn't seem quite right then the dive is over. Sort it out on the surface.
Noise (bubbles), gas consumption and too high an FiO2 equals major leak.
Can stay on "loop" as open circuit in these conditions in the sameway as if a sonic valve problem.
A flooded scrubber does not have major effect on bouyancy.
These are very clever units. ( many features which add to safety ).
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Was able to drain the scubber and bags while others completed their dive. During their surface interval did a ten minute spell on the loop to check the scrubber was still functioning. (So long as gas pathway restored and using a virtually insoluble materal will work as needs to be damp/wet to work anyway). Was then able to change to a full cylinder and drop in for the second dive (60 minutes).
Several lessons learnt and greater confidence in these units,
Neil |
Thanks for sharing this,it is an interesting post.
I must say I read this with horror and amazement that you got away with it so easily and was unaware that it was still possible to even breathe the unit in such circumstances.I would have bailed out,as you say,at the first sign there was something not right and sorted it out on the surface.But I have also learnt something from this as well.I was unaware that the scrubber would function when or after being completely flooded...I know it gets a bit damp sometimes and even a bit solid but I thought when water was added it no longer functioned,surely the kitty litter is at least porous and the whole scrubbing reaction would be greatly retarded if there was water coating everything...what about the 'caustic cocktail' effect?I thought you would get a mouthful of sodalime solution through the inhalation hose? With all due respects,I'll think I'll leave trying that one myself.
I think about the worst I ever experienced was in my first year with the unit when I got a lot of water in the exhalation hose as a result of getting hit by a wave on the surface starting a dive....this was my early days with the unit and I did not like the feeling of breathing through a bubbly straw which seemed to get worse... so at 25m I baled out onto the 3l and very glad I was that I had a stage 3l as well.It gave me a fright but was probably me being over cautious .Really nothing compared to this though.