RMV Spinoff from Accident & Incident Discussion - Northernone - aka Cameron Donaldson

[lv2dive]

There are quite a few guys in cave country (FL) with similar RMV/SAC rates (mid to high .2’s) As a female with decent gas consumption, it’s incredibly frustrating to be the one turning the dive on gas.

I don't mean to be offensive or disrespectful, but I find those rates extremely, reapeat extremely, hard to believe.

 

[rjack321]

I know some extremely well known and highly regarded divers with great SACs who absolutely do skip breathe. They won't admit it in a public forum like this because of the expected reaction, but they do it.

I have kind of assumed this is the case and that being "so relaxed and comfortable" is actually years worth of acclimatizing to CO2. But I have no way to measure this.​

A former dive buddy of mine consistently had a RMV of .25-.27 in Mexico caves (in a drysuit!). He was a tall male and it drove me crazy bc I was ALWAYS the one who called the dive.

I have no idea how you would evaluate whether this was or was not skip breathing.

 

[rsingler]

I don't mean to be offensive or disrespectful, but I find those rates extremely, reapeat extremely, hard to believe.

As an anesthesiologist who routinely ventilates patients and monitors their pCO2, I can tell you that a resting RMV of 0.21 cfm is compatible with zero CO2 retention for an average sized person. Your metabolic rate does not decrease under anesthesia, so this is a reasonable starting number for a diver at rest.

So if someone tells me that an experienced diver had an RMV "in the mid to high 0.2's" I would not automatically dismiss the claim. I can't get that low, when swimming leisurely, but I keep trying.

 

[johndiver999]

Hi @johndiver999

OK, my last attempt at an estimate. As before, we cannot estimate Cameron's gas consumption because we don't know his profile, RMV, or computer settings

So, in our hypothetical dive we spend 40 minutes on the shallower reef, say around 60 ft, and come close to NDL. We then make a brief dive over the wall, down to 150 ft, until we have almost a half hour of deco. We satisfy our deco obligation while getting back to shore and end the dive. So, this dive is done with conditions that make the dive doable. Any of the previously mentioned factors could make this dive undoable, such as ripping current, strong downdrafts, scooter failure... That would nullify any chance at an accurate estimate. The first half of this dive is under reasonably benign conditions, one eighth of the dive is the deep portion, three eighths are deco and return to shore. Again, arbitrarily, 50/85 is used. The first table uses an average RMV for the entire dive of 0.5 cf/min, the second table uses an RMV of 0.75 cf/min for the entire dive. You can judge for yourself how to interpret these RMVs, I consider both on the high to very high side for a doable dive. At the lower RMV, there would be plenty of gas in two AL80s to complete the dive. With the higher RMV, there would be insufficient gas to complete the dive. Though extremely artificial, this exercise was useful for me.
View attachment 510882 View attachment 510883

Thanks very much! That is exactly the type of analysis I was hoping for. Although you seem to be skeptical of the value of the exercise, I think it helps bracket the range of possibilities- assuming the dive is consistent with the assumptions.

Not to seem unappreciative, but if someone were planning a dive such as this, I would think the assumption of the loss of one tank (at the worst possible time) would need to be included as well.

As for some of the super low rmvs being mentioned, those are foreign to me- far from my personal experience, but doesn’t negate their validity. Cameron talked about practicing non breathing emergency ascents on other posts that were boardering on unbelievable, so along with direct observations from others, it sounds like we have a good bit of evidence that his personal air use or physiology is exceptional.

 

[cerich]

I don't mean to be offensive or disrespectful, but I find those rates extremely, reapeat extremely, hard to believe.

it's typical resort instructor consumption.. just saying. Mine was that low when I was in Cayman, it isn't 20 years and 40 lbs later however, but it's still better than most divers

 

[scubadada]

I can give some input into Cameron's SAC rate or RMV if you prefer. I just checked a shore dive we did on 1-1-2018. We swam into a current for the first 2/3 of the dive. Cameron carried his big camera rig and was using some odd fins he had never worn before because he was testing some silly fins for someone and let our other friend use them for the dive to try out so Cameron was using his full foot whatevers that were somebody's cast offs. He took some great photos that required some positioning and we found some lion fish in nooks and crannies along the way. I started with a full AL80 and he started with an AL63 that had 2,000 psi. We finished the 90 minute dive essentially empty(176 psi) in waist deep water. The depth averaged 20 feet and max was 39. That comes to around .28. I think he told me on several occasions that his sac was in the mid to high .2s on cave dives with a camera and no scooter and his mom was around .23. He sipped air. I can't say what happened when he got into a stressful situation because I never saw him stressed. I've read about it here though.

I don't have a problem accepting that Cameron might have had an average RMV in the high 0.2s cf/min, in fact, I assumed it was on the lower side. That explains why I chose to use an RMV of 0.5 in my first calculation (post #2). It also partly explains why I call 0.5 and 0.75 on the high to very high side in my second calculation (post #18). He is young, fit, and, by all accounts, an experienced, relaxed, excellent diver. I am not young, 65 years old, but am reasonably fit. I'm also a reasonably experienced, very relaxed, good, but not excellent diver. My average RMV for the last nearly 1,300 dives is O.36 cf/min. I do not skip breathe. The best part of an average value is that it represents all kinds of conditions, representing the entire range of what you have dived. The variation in RMV is less than many would expect, 95% (+/- 2 SD) of my RMVs are between 0.28-0.44.

There have been 2 polls on SB asking, "What is your average RMV". The first was posted in 2009, I posted the 2nd in 2016. Of course there are caveats for polls posted on SB. The distribution is what you would expect, the mode is 0.4-0.49 cf/min and the median is 0.5-0.59 cf/min. Nearly 15% of respondents had an average RMV of <0.4 cf/min. An elite group, of a little over 2%, reported an average RMV of <0.3 cf/min.

 

[Compressor]

Air consumption of 0.25 is insanely low. Makes my SAC of 0.5 ridiculously high. I know he was in an insanely good shape so it is definitely possible to have a low SAC of 0.25.

I read a lot of speculation about his disappearance but the truth is that we don't know. There is no enough data. If god willing he is alive, he will tell us. If he is not and his body is recovered (we can find out from the autopsy and his equipment) and if he body not recovered, then it will all be speculation IMO. It's TOO early to give up. I'm sorry but I will not give up and not planning on it for quite sometime.

 

[Celt]

I know some extremely well known and highly regarded divers with great SACs who absolutely do skip breathe. They won't admit it in a public forum like this because of the expected reaction, but they do it.

Dead right, diving deep air you want to use the least amount of bottom gas as possible, while on the bottom i keep my breathing rate to the bare minimum.

 

[scubadada]

Even us older divers get in a good one every once in a while

 

[cerich]

Dead right, diving deep air you want to use the least amount of bottom gas as possible, while on the bottom i keep my breathing rate to the bare minimum.

it doesn't work like you seem to think it does, breathing rate will not affect your on gassing.