RonMicjan

I would like to relate a couple incidents that happened recently, one during a CCR course I taught and another during a cave dive down in Mexico.. These reports are also quite relevant to the CO2 video that HSE has recently released.

This is an account of a CO2 hit that a student took in the first 15 minutes of the first open water dive on the Meg CCR.
As we know, most CCR systems are a bit bottom heavy, with a breathing loop full of gas near the top of the unit and inverted cylinders, valves, and regulators at the bottom, most units tend to trim to the up position. This leads to creative and sometimes dangerous ways to top load the unit with some extra weight. I was taught during my first student course to take a long slender soft weight, normally used for ankle weights for inexperienced dry suit divers, and drop it in the sleeve behind the OTS (Over the Shoulder) or front mounted counterlungs, this distributed 2-4 lbs (depending on the size used) near the top chest of the diver and provided needed trim weight. I have frequently suggested this to my diving students for trim purposes and it has worked well.

In this particular case, the diver noticed that his trim in the pool portion of the training was as usual bottom heavy and I suggested the ankle weight addition. That evening, he improvised a solution, not having any ankle weights, he took 2-2lb soft bag weights and using a rather ingenious method with tape and a zip tie, attached the soft weight to the top of the counterlung mount and dropped it into the sleeve behind the CL. What wasn’t apparent at the time, nor during the pre dive or pre breathe, was that in a diving position that weight ended up trapped directly behind the counterlung T piece almost completely blocking it.

After entering the water and doing bubble checks and buddy communication, we descended a slope to about 80 fsw and swam along the slope, about 8 minutes into the dive I noticed the 2 students drifting apart underwater, I had previously stressed buddy contact during all portions of the dive so I made contact and motioned that they close the increasing distance between them, the diver falling back was at this time beginning to feel the onset of symptoms from CO2 poisoning, including increased respiration rate and mild confusion. This diver is a very experienced technical OC diver as well as an OW instructor, he also comes from a military background and has an ingrained attitude when it comes to toughing out a bad situation. Despite classroom admonition that “When in doubt, Bail Out” and the full CO2 doom and gloom talk, he continued to “tough it out”.

What was happening was a serious increase in the work of breathing on the loop, the meg has always drawn kudos on its ease of the WOB effort required to dive it, however with the 2 lb soft weight pushing the back side of the counterlung up against the opening for the T piece, the usual ease of breathing was seriously restricted. Even the ADV was difficult to activate, as its mechanical plunger was just under the shoulder created by the weight packed under the T piece. The diver was building up CO2 in his tissues at an alarming rate. There was nothing wrong with the scrubber stack on the rig, what was happening was the diver was short stroking his breathing and the CO2 laden gas was not making it into the loop, instead staying in the divers lungs and trachea.

About 13 minutes into the dive he finally stopped swimming and turned to me and gave me the see-saw hand signal that something was wrong, I had already been checking the HUD for proper PO2, but I also picked up and checked the primary handset for PO2 levels also. (The HUD and Primary are completely separate systems on the meg) I looked at his eyes and they were clear and responsive and I asked him with a hand signal what’s wrong? He again gave the something’s wrong signal and I said (through the FFM) BAIL OUT! He made a motion to turn on the ADV and turned away from me to his buddy and started swimming up slope to the surface, after about 30 seconds, he began swimming in a circle instead of continuing upslope and I grabbed him and looked in his eyes which were less clear and responsive than before, I took hold of his harness and flashed a light at our guide, gave and received the “thumb the dive” signal, told the guide to buddy with the other student and began swimming the diver straight to the surface. On the way up his eyes did not clear up but he was assisting by fining and dumping his BCD and I noticed the counterlungs were still moving with short rapid respiration. We reached the surface and I pulled the loop out, shut it off and inflated his BCD. His respiration was quite high but his consciousness level returned at once. We discussed what was happening and he just said it was hard to breathe and the ADV wasn’t working well, he was having difficulty getting gas. We swam slowly back to the entry point, about 10 minutes, and he sat on a log to catch his breath, our guide brought oxygen from my vehicle for him to breathe and he remained on it for about 20 minutes.

I walked his meg into the water and held it under to look for any gas leaks, I also held it under water while I breathed on the loop for 10 minutes, the rig was working fine, but I was also not wearing it, with the weights between the T piece and counterlungs. This was quite puzzling why he would take a CO2 hit on the rig, but I was not getting any symptoms, if the scrubber was compromised, it should be the same on the surface. I popped the head, with the guide and the buddy watching and did a pos and neg on the sensor carriage, pulled the scrubber, already knowing it was good as I had stood over these guys during their pre-dives, checked all o rings relevant and still there was nothing that was revealed why he took a hit. About this time he mentioned how difficult it was to get gas from the ADV on the way down so I looked closer at the counterlungs and then found the weight tucked behind the T piece. He had showed this to me after he set it up but I didn’t think anything of it, in fact I thought it was quite a nifty solution considering the absence of an available ankle weight.

In conclusion, with all of us on the surface and disaster averted, I see a couple things that could have been done better.
I should have noticed the significant difference between the result of using a shorter fatter 2lb soft weight and the ankle weights I had previous experience with.
The diver should have bailed out sooner, rather than “toughing it out”.
The standard bailout procedure of Dil Flush/Open loop would not have worked in this instance, (due to the partially inhibited ADV) but going to an OC bailout would have.
Looking back at when he first signaled something’s not right, I should have not lost physical contact with him, even for one moment. The 30 second delay could have been critical, luckily it was not.
I would not ever recommend any thing be put behind the counterlungs again, trim weights can be attached at the top of the Backplate, along the sides of the Backplate, between the Backplate and main unit (this is where I place them, clipped to the soft handle and dropped between the wing and plenum and along the cylinders. The RBW store is also selling solid SS handle replacements for the meg that position 2 additional lbs at the top of the unit with no possibility of compromising the loop.

Lessons learned
Bailout at the first sign of trouble, tough it out only if people are shooting at you.
Try and think through all possible problems with a change of gear configuration.
Don’t let a student that is having problems get away from you.

Another co2 issue came up recently on a cave dive, the dive was planned for 2 teams to visit the same area, a three man team on Meg CCR’s were going to lay the approach line to the main cave line and a pair of newly certified OC cave divers were going to follow the line in a few minutes after. The dive site was the Monster, a 51 foot high stalactite about 1500 feet downstream of Chuk Mool Cenote. The OC divers were not sure they could make that length of penetration on their thirds and so we were going to do the line laying so they could just cruise in. I had lead and set the primary line in to the cave line just beyond the cave warning sign, checked that my two buddies were behind me I set out at a somewhat brisk pace, making sure to not slow the OC folks down. (Diving on CCR’s in caves, I tend to run pretty slow, as we generally have 5-6 hours duration on the rigs. (all three of us were running radial scrubbers) and no need to hurry. But on this dive, I didn’t want to slow the OC divers down from running their usual pace and give them time to not only make the Monster, but have a few minutes to enjoy it before heading back. So we headed out, frequent checking confirmed my 2 CCR divers were still behind me and I also noticed a couple more lights in back letting me know the OC divers had caught up too. It was hard to see individual people due to the halocline that is present throughout most of this particular dive. At about 1350 feet in, I was signaled by the #3 man that the OC divers had turned the dive, and were not going to make it the rest of the way and he also signaled me to slow down, which I would have done anyway with the OC folks bailing out. Upon reaching the monster room, the number 3 man had fallen back a bit and actually stopped at the entrance of the room. I was tying a light to the line for a reference while examining the formation, and noticed that only one diver was next to me, I asked him where #3 was and he pointed back a bit and I saw 3’s light back about 40 feet and figured he was giving us room to set the light and an arrow. He showed up a few moments later and was having a bit of trouble with buoyancy; he was resting on a bit of rock for support and signed that he needed to catch his breath. We hung for a couple minutes until he signaled OK, then we all swam over to the formation and I videoed a few minutes of the giant stalactite. A very cool site BTW, something that every cave diver needs to visit. We met back at the line where the light and arrow were set up and the plan was to continue farther into the cave system, but with #3 having the earlier issue, I suggested a turn and it was agreed by all, we headed back, out of the cave. I ran the video on the way out, catching nice side views of the lead and middle diver, as well as some great formations. About 10 minutes into the return trip I noticed #3 was beginning to slow down and get a bit vertical (feet up) in the tunnel, getting vertical is not unusual for #3 and I wasn’t too concerned with the slowing up either, as it gave me more time to line up shots on both sides of the tunnel, but this was actually an onset of co2 poisoning.

I continued to take video but noticed #3 slowing even more and spending more time fins up, I swam forward to him and asked if he was OK, he signed back he was OK and his eyes looked fine and he was responsive. He did pick the pace back up and resumed a cleaner technique but this only lasted a couple minutes and he slowed up again and lost trim. I was becoming concerned and swam up to #2 and asked him to hold the camera system and I swam forward again to ask #3 if he was OK. He waved me off rather annoyed and with a hearty “F off” and seemed just fine, but another couple minutes later he slowed and began kicking rather uncoordinated and not at all in rhythm. At this point, I knew there was something definitely wrong and handed off the camera to #2 again determined to get #3 to bail off the loop. As I swam forward, I noticed #3 fumble a bit for his stage regulator and his kicking get quite uncoordinated. I came alongside and pulled the reg from its attachment and shoved it at him and said “BAIL OUT”. He took a second to focus and then shut off the DSV, swapped it for the OC reg and started breathing off it, I went into touch contact and began swimming along side helping him swim. He waved me off after a couple minutes and signaled he was OK, and that I should take the lead out, which I did. We continued progression out of the system, noting that the OC divers cookies were gone from the line we set, we left the reel in and made for the open water.

#3 told me that until he got off the loop and onto the OC reg, that he didn’t feel that anything was wrong and was wondering why I kept asking him if he was OK. He even was annoyed the second time I asked, but figured that when I asked the third time that something must have been amiss and readily accepted the OC reg. When he started breathing OC gas, he said that the world opened up around him and that was the clue that something was seriously wrong. His head cleared quickly and at that point waved me to take the lead. We have no way of knowing what the Pco2 of his loop was when things started going badly, but expect that it began on the way into the system, not on the way out. He doesn’t usually have any problems swimming at a faster pace and it was unusual for him to need to stop and catch his breath. We should have turned the dive then, rather than tour around the formation.

The dive shop had two kinds of sorb available, Sodasorb 8-12 at $180 a bucket, or medical sorb at $100 a bucket. #3 had decided to use the medical stuff, having had experience with it on a prior visit. #2 and myself were both using sodasorb. #3 had run completely through a fill of the medical sorb in about 3 hours on the stack and with the heavier exertion going in, had reached breakthrough.

Lessons learned.

Medical sorb NOT!
Turn the dive at first symptoms.
Difficulty catching your breath, is a symptom!
Don’t get annoyed with your buddies if they ask “are you OK”, they may know something you do not.
CO2 is an insidious little bastard that will kill you if you don’t respect it. It can sneak up on you and seriously ruin your day.
When in doubt, Bail Out! Live to dive another day. If you even THINK you might be having a problem, do a quick flush and see what it does for you, fresh gas is cheap and easy to come by.

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