(I considered putting this in Accidents/Incidents, but I figured the narrower audience here would be beneficial.)
An eventful dive this weekend, my buddy experienced an internal boom -- gas was being rapidly added to the loop. He's a relatively new CCR diver, and his training was essentially, "shut the valves". When he drilled this during class with flashcards, I'm sure there was little sense of urgency. In this case, the urgency was present due to a deco obligation and rapid upward trajectory. (He did surface; but fortunately, it was a fairly shallow ceiling with a quick return and plenty of extended time on O2. No complications.) My suggestion for him moving forward was to drill the priorities (#1 breathing, #2 buoyancy): immediately going head down/kicking and venting the counterlung (addressing buoyancy) while switching to BO with the other hand (addressing breathing, assuming he didn't know whether it was O2 or dil being injected). THEN solve the issue: 1) figure out which gas based on PO2 -- he was shutting both valves simultaneously, as he didn't know which was the problem or think to check the PO2 in the heat of the moment. (Turns out it was dil being added.) Then 2) shut the problem gas source off. Hopefully it's the tank needing the available hand (as the other is still venting as needed to avoid ascent/descent). If not, then perhaps alternately close a bit then vent and repeat. Or perhaps switch to dumping from the wing with one hand while closing that valve with the other (and hope you get it closed before the wing empties). Or even having the buddy shut down the tank, since with depth stabilized by venting, they should be there to help. (On that note, where was I? I was about 5 ft away when it all started and chased him up from 40 ft but couldn't catch him before I slammed on the brakes at 25 ft due to a 20 ft deco ceiling. Not even sure I could have stopped him, for that matter, as he wasn't venting very quickly through the nose. He also held the DSV firmly in his mouth rather than let the pressure expel it.)
Afterward, he said he reacted just as he had rehearsed in class; however, the earlier simulation wasn't realistic enough (at least in my view, as it lacked the buoyancy/venting attribute). FWIW, my training (and I suspect that of most others) was similar.
The main reason for this post is to suggest that everyone consider rehearsing their response in such a scenario. Mash on the dil inflator and see if you can deal with it without blowing up. (While within NDL, of course!) Yes, a hand will be tied up on the MAV, so not exactly the same, but a) recognition of rapid onset of buoyancy / loop pressure and b) quickly venting the loop are the priorities. After that, specifically looking at the PO2 (envisioning the red alarms or lack thereof) would be a priority and then dealing with that specific gas source while continuing to vent.
The other point of this post is to discuss other potential options. For instance, I was trained to primarily vent via the corner of my mouth, with the nose typically used for very slight burping. I rather suspect it could keep up with the gas addition without even going head-down & venting from the counter lung pull-dump. It's definitely on my list of things to verify on my next dive. Another buddy would have simply vented by opening the DSV, as that's his normal method of venting when bailed out. My training was also to close the valve, but in the case of dil injection, I can also disconnect my dil feed (QC6) in a heartbeat. Perhaps that's a better initial step in that case, followed by shutting down the valve.
I feel I've been pretty good with BO practice (incl. ascent), but this might have caught me by surprise as well. Hard to say, without being in the moment. This will definitely be going on my list of things to periodically drill. I would love to hear if you have recently drilled a similar (or any emergency, for that matter) or what your "go-to" approach to rapid gas addition might be.
An eventful dive this weekend, my buddy experienced an internal boom -- gas was being rapidly added to the loop. He's a relatively new CCR diver, and his training was essentially, "shut the valves". When he drilled this during class with flashcards, I'm sure there was little sense of urgency. In this case, the urgency was present due to a deco obligation and rapid upward trajectory. (He did surface; but fortunately, it was a fairly shallow ceiling with a quick return and plenty of extended time on O2. No complications.) My suggestion for him moving forward was to drill the priorities (#1 breathing, #2 buoyancy): immediately going head down/kicking and venting the counterlung (addressing buoyancy) while switching to BO with the other hand (addressing breathing, assuming he didn't know whether it was O2 or dil being injected). THEN solve the issue: 1) figure out which gas based on PO2 -- he was shutting both valves simultaneously, as he didn't know which was the problem or think to check the PO2 in the heat of the moment. (Turns out it was dil being added.) Then 2) shut the problem gas source off. Hopefully it's the tank needing the available hand (as the other is still venting as needed to avoid ascent/descent). If not, then perhaps alternately close a bit then vent and repeat. Or perhaps switch to dumping from the wing with one hand while closing that valve with the other (and hope you get it closed before the wing empties). Or even having the buddy shut down the tank, since with depth stabilized by venting, they should be there to help. (On that note, where was I? I was about 5 ft away when it all started and chased him up from 40 ft but couldn't catch him before I slammed on the brakes at 25 ft due to a 20 ft deco ceiling. Not even sure I could have stopped him, for that matter, as he wasn't venting very quickly through the nose. He also held the DSV firmly in his mouth rather than let the pressure expel it.)
Afterward, he said he reacted just as he had rehearsed in class; however, the earlier simulation wasn't realistic enough (at least in my view, as it lacked the buoyancy/venting attribute). FWIW, my training (and I suspect that of most others) was similar.
The main reason for this post is to suggest that everyone consider rehearsing their response in such a scenario. Mash on the dil inflator and see if you can deal with it without blowing up. (While within NDL, of course!) Yes, a hand will be tied up on the MAV, so not exactly the same, but a) recognition of rapid onset of buoyancy / loop pressure and b) quickly venting the loop are the priorities. After that, specifically looking at the PO2 (envisioning the red alarms or lack thereof) would be a priority and then dealing with that specific gas source while continuing to vent.
The other point of this post is to discuss other potential options. For instance, I was trained to primarily vent via the corner of my mouth, with the nose typically used for very slight burping. I rather suspect it could keep up with the gas addition without even going head-down & venting from the counter lung pull-dump. It's definitely on my list of things to verify on my next dive. Another buddy would have simply vented by opening the DSV, as that's his normal method of venting when bailed out. My training was also to close the valve, but in the case of dil injection, I can also disconnect my dil feed (QC6) in a heartbeat. Perhaps that's a better initial step in that case, followed by shutting down the valve.
I feel I've been pretty good with BO practice (incl. ascent), but this might have caught me by surprise as well. Hard to say, without being in the moment. This will definitely be going on my list of things to periodically drill. I would love to hear if you have recently drilled a similar (or any emergency, for that matter) or what your "go-to" approach to rapid gas addition might be.
