Impaired ventilation at depth due to gas density?

[DrHarry]

There have been 2 near fatal CO2 hits in Australia where the survivors commented afterwards, that even with an OC reg in their hand they "knew" it was impossible for them to even consider taking the DSV out of their mouth to replace it with a reg. They knew what the problem was, they knew what they had to do; but they were sure they would drown if they tried the exchange.

Both lost consciousness underwater and were very lucky to survive.

These cases make me believe a BOV is essential.

 

[GaryL]

...you will still be breathing through the scrubber

My hint must have been too subtle for John Open loop or scr at depth is not really an option beyond a few moments imo.

No idea about the design concept; it works. That's good enough for me.

 

[heyydude]

There have been 2 near fatal CO2 hits in Australia where the survivors commented afterwards, that even with an OC reg in their hand they "knew" it was impossible for them to even consider taking the DSV out of their mouth to replace it with a reg. They knew what the problem was, they knew what they had to do; but they were sure they would drown if they tried the exchange.

Both lost consciousness underwater and were very lucky to survive.

These cases make me believe a BOV is essential.

Harry,

I know you've heard this story before from me, but I'll repeat it for those who haven't - if it weren't for a BOV (one of the early Tracy Robinette versions from the mid-90's), and my partner, John, flipping me over to Open Circuit at 260 fsw, I would not be here today. My CO2 hit was so bad, I could not even think, even though the "answer" was right in front of me (the BOV).

That's why, when we introduced the HH CCR, I insisted that every single one comes standard with a BOV.


On another note: This is BY FAR, one of the most INTERESTING conversations I've seen about CCR diving in a forum for a long time - So much information coming from such amazing sources (Harry, Dr. Mitchell, divers like Mark Chase, etc), that I'm enjoying sitting back and reading it. Just fantastic stuff, guys. Thank you.


Kevin.

 

[GaryL]

I think that when people mention their co2 hit it would also be useful if they mention the cause of it, if known.

 

[Randy Thornton]

Like most I was taught if i thaught I had a C02 event i should dill flush as a first responce????? I see this as insain. If your scrubber or unit has failed to scrub C02 to that point its not going to magicly heal its self now. The only benifit would be to reduce the C02 getting through, your not going to stop it.

Mark, I hold CCR Instructor credentials for 4 different agencies and I can tell you that none of them currently teach that a dill flush is the first response for a CO2 event. Virtually all of them advise bailout as a first response to suspected CO2 problems. I can remember that in the very early days, there were discussions that perhaps a good dill flush would be adequate, but all agencies with which I am familiar currently teach that for CO2 problems, bailout is the appropriate response.

Regards,
Randy

 

[DrHarry]

Hi Gary, good point because I think that a CO2 hit that comes on gently is a different animal to one that is sudden and overwhelming. I can think of one minor one I experienced from swimming in current on the KISS where I over breathed the scrubber. I got breathless and got a headache, but was able to stop, rest and bailout for a short time to get settled. I went back on the loop and was fine. That may not have been sensible in retrospect but all was well.

The two cases I mentioned that were catastrophic were more sinister. One (that Simon knows well and helped treat i think) had a problem with a flapper valve and the other, had an OTS counterlung incorrectly attached so it floated up high and (I think) created a massive WOB issue.

I imagine the recent sad death where the cannister/cartridge was left out during a shallow dive would have had rapid overwhelming consequences.

So perhaps in slow onset cases it is reasonable to think you will manage your bailout as long as you recognise what is happening in time. But in sudden onset cases due to mechanical/equipment issues you may not have the time or ability to self rescue. Even WITH a BOV in Kevin's case.

I have switched a mate's BOV to OC when he was looking a bit glassy eyed and not responding to signals. Yes...I am a BOV fan!

 

[Randy Thornton]

BOVs are bulky, finicky, heavy and somewhat uncomfortable. That said, in my humble opinion, a good operational BOV is one of the most significant CCR safety improvements introduced to the CCR world over the past 10 years, and I would not consider doing a serious CCR dive without one.

 

[Mike Ferguson]

I posted this about a year ago on a different thread about BOV's when people were saying 'I'll just switch to an OC reg if I get a hit'. i haven't changed my mind in the intervening period.

I'm not sure what constitutes a full blown hit and what constitutes a minor hit. It's only happened once but the time taken to go from a bit of puffing and panting returning to a shot line in 25m of water to breathing so hard it hurt was a matter of seconds. My bailout reg may as well have still been on the boat as strapped to my bailout cylinder 12" from my face.

It's hard to describe but I'll try. I've been diving for over 30 years and have had some interesting experiences in that time. I thought I was pretty well unflappable underwater. This was outright, primeval panic from the spinal cord not the brain, it felt like I was breathing a vacuum even though gas was going in and out of my lungs. I had no control over my breathing rate at all.

After reading about CO2 hits I had bought a BOV and was able to switch to it with the thought of stabilising my breathing. No such luck. I was now chugging through gas on the bottom without any change in my breathing rate. The BOV breathed like crap at these high flow rates and there were so many bubbles my buddy thought that I had blown a hose, but I was at least able to breathe as I gave up all pretense of regaining the shot 6 feet away and blew for the surface. I managed to calm my breathing enough to do a couple of minutes of stops before surfacing. It took about another 10 minutes for my breathing to return to normal.

I checked my kit afterwards, no floods, no issues with flapper valves. scrubber had done a 1 hour dive the day before to 58m and I was 45 minutes into a 27m dive. All I think happened was that I produced more CO2 than the scrubber could remove at the rate I was breathing.


I came to two conclusions afterwards:

1. without the BOV I would have been in a whole different league of shit that day.

2. if you have a BOV connect it to something big as it may be some time until you can comfortably get off it onto a real bailout.

Mine at the time was connected to onboard dil, the theory being to provide sanity breaths to allow me to switch to a bailout reg. So much for that theory, there wasn't a lot left in a 3L when I surfaced from 25m. It's now plugged into offboard gas.

I don't sell BOV's and haven't seen one yet I really like for the 99.99% of the time that you don't need it. I am just saying what happened to me.

It's your life, make up your own mind. Personally I'm glad someone warned me in advance and I bought a BOV.

two years have gone by and the slightest hint of feeling short of breath these days and I'm still heading up with one hand on the BOV ready to switch.

 

[Mike Ferguson]

I've had two CO2 events, in neither case did I think I must get some more kit.

what other than a completely new rebreather?

I once had a mild gradual onset episode after doing the same two deep dives on one scrubber trick where I could have switched to an OC reg if it hadn't resolved when I legged it back up the shot to get above 40m asap, but the rapid onset hit made me very wary of my own ability to switch.

 

[Michael Thornton]

Like most I was taught if i thaught I had a C02 event i should dill flush as a first responce????? I see this as insain.

Was this possibly on a classic inspo with no BOV where many believed a Dil flush was a faster way to get a breathable gas in your lungs than taking the time to bail to off board?

I don't hear a dil flush taught as a first response to hypercapnia very much anymore especially on units with BOVs

 

[Mark Chase]

Was this possibly on a classic inspo with no BOV where many believed a Dil flush was a faster way to get a breathable gas in your lungs than taking the time to bail to off board?

I don't hear a dil flush taught as a first response to hypercapnia very much anymore especially on units with BOVs

I did MOD 1 on the Inspo Classic in 2004 and Mod3 in Jan 2005 both TDI so things may have changed in the last 9 years.

Instructor used flash cards and throughout the training he would hit you with a flash card at random moments. Things like Low PP02, High PP02, Co2

Responce to Co2 was dill flush

Its a while back so I hope Paul will forgive me if I have this wrong, but from memory basicly Mod one was more a "if in doubt bailout" course where as Mod3 we were taught "on loop solutions"

Most of the divers I dive with went CCR around the same time as me (we were all deep trimix OC and all switched at the same time) and I have discussed the whole C02 issue with them on days where we were sat arround on loyal Watcher in the evenings and many have intimated that dill flush, open loop and SCR were viable responces to C02. One asumes as per their training.


If things have changed now I am very pleased to here it.

ATB

Mrk

 

[Igor]

There have been 2 near fatal CO2 hits in Australia where the survivors commented afterwards, that even with an OC reg in their hand they "knew" it was impossible for them to even consider taking the DSV out of their mouth to replace it with a reg. They knew what the problem was, they knew what they had to do; but they were sure they would drown if they tried the exchange.

Both lost consciousness underwater and were very lucky to survive.

These cases make me believe a BOV is essential.

What caused the Co2 hit in these 2 incidents?

 

[DrHarry]

What caused the Co2 hit in these 2 incidents?

The two cases I mentioned that were catastrophic were more sinister. One (that Simon knows well and helped treat i think) had a problem with a flapper valve and the other, had an OTS counterlung incorrectly attached so it floated up high and (I think) created a massive WOB issue.

 

[lizardland]

There have been 2 near fatal CO2 hits in Australia where the survivors commented afterwards, that even with an OC reg in their hand they "knew" it was impossible for them to even consider taking the DSV out of their mouth to replace it with a reg. They knew what the problem was, they knew what they had to do; but they were sure they would drown if they tried the exchange.

Both lost consciousness underwater and were very lucky to survive.

These cases make me believe a BOV is essential.

Yep, that sounds all too familiar. I had a CO2 hit at about 30m and remember just how hard it was to get off the loop. I've posted it before on the other place but a brief summary: I was diving a KISS, the Paragon BOV was shagged so was diving it as a straight DSV. I was pissing about just doing some drills, managed to blow a big gob of water straight into the loop (I think I'd dumped the loop with the mouthpiece open for a couple of seconds), took a few breaths and then bang, someone battered me round the head with a hammer.

My breathing rate went through the roof, I knew EXACTLY what I had to do, I even had the offboard reg in my hand. But the idea of stopping breathing for the few seconds it took to swap to the reg just seemed utterly ridiculous. I clearly remember thinking I could keep breathing, how bad would inhaling a bit of water be? The weird think was that mentally I felt very calm and collected, I'd accepted my fate whereas physically I was working like a steam train. I don't know how I got it together but swapping to the bailout took more mental effort than I can remember.

CO2 really scares me. I always love reading all the "just calmly swap to an offboard reg" bollocks. The impairment is nothing like N2 narcosis, it's almost like CO2 impairment triggers a personality change. I remember reading about experiments with carbogen and it just makes me think CO2 triggers something deep in the brain that should never get triggered.

 

[gianaameri]

...it's almost like CO2 impairment triggers a personality change. I remember reading about experiments with carbogen and it just makes me think CO2 triggers something deep in the brain that should never get triggered.

Interesting reading:

1. Carbon Dioxide Therapy. A Neurophysiological Treatment of Nervous Disorders, 1950, Meduna.

2. Effects of CO2 and N2 Partial Pressures on Cognitive and Psychomotor Performance, 1991, Fothergill, Hedges, Morrison

 

[heyydude]

I think that when people mention their co2 hit it would also be useful if they mention the cause of it, if known.

Hey Gary,

I'll freely admit the cause of my CO2 Hit: My own Stupidity in listening to a guy who considered himself a "Guru" back when I was still relatively new to CCR diving... I had a problem with water leaking into my FFM when I was diving the Mark 16, and the "Guru" told me to just "blow it out through the exhale hose, then purge the loop using the Diluent Manual Add button, and it'll flush out of the counterlung..."

Uh huh... So, on a 260 fsw dive (always a great place to run tests, at 260 in murky water...:uhh, I kept blowing water out of my exhale hose into my "counterlung" until I started having problems breathing - couldn't catch my breath... Finally, I was about to rip off my mask, bail to the surface (after a bottom time of 20 minutes, I would have been dead by the time I hit the surface), anything just to get away from the panic that flooded my mind. I closed my eyes while kneeling on the bottom, trying to calm myself, when my pal John looked over and thought that I had passed out, so he flipped me over to Open Circuit... Make a long story short, my head cleared enough for me to realize what was going on (hypercapnia) - I burned through all my gas during deco, and once back on the boat, explained to everyone what was going on down there...

Back on land - I take apart the 16 and notice that the exhale port goes to the base of the Scrubber, and all I was doing was blowing water into the scrubber over the course of the dive. Yes, I am a Big Dummy for not learning enough about the rig to understand that simple (and obvious!) fact... I vowed to learn every single piece of the machine and what it did and how...

And I vowed to never listen to self-styled "Guru's" again...

Kevin.

 

[Michael Thornton]

Hey Gary,

I'll freely admit the cause of my CO2 Hit: My own Stupidity in listening to a guy who considered himself a "Guru" back when I was still relatively new to CCR diving... I had a problem with water leaking into my FFM when I was diving the Mark 16, and the "Guru" told me to just "blow it out through the exhale hose, then purge the loop using the Diluent Manual Add button, and it'll flush out of the counterlung..."

Uh huh... So, on a 260 fsw dive (always a great place to run tests, at 260 in murky water...:uhh, I kept blowing water out of my exhale hose into my "counterlung" until I started having problems breathing - couldn't catch my breath... Finally, I was about to rip off my mask, bail to the surface (after a bottom time of 20 minutes, I would have been dead by the time I hit the surface), anything just to get away from the panic that flooded my mind. I closed my eyes while kneeling on the bottom, trying to calm myself, when my pal John looked over and thought that I had passed out, so he flipped me over to Open Circuit... Make a long story short, my head cleared enough for me to realize what was going on (hypercapnia) - I burned through all my gas during deco, and once back on the boat, explained to everyone what was going on down there...

Back on land - I take apart the 16 and notice that the exhale port goes to the base of the Scrubber, and all I was doing was blowing water into the scrubber over the course of the dive. Yes, I am a Big Dummy for not learning enough about the rig to understand that simple (and obvious!) fact... I vowed to learn every single piece of the machine and what it did and how...

And I vowed to never listen to self-styled "Guru's" again...

Kevin.

Glad you are ok, but what we really want to know . . . Is the 16 ok? Ha ha.
Just kidding thanks for sharing. Those of us who are lucky enough to not have had a CO2 incident can learn a lot from others accounts.

 

[Fireman]

SCR because we where discussing gas density and very deep dives where bail out is problematic. It would see to me that venting some gas (high in CO2) and putting fresh gas in (no CO2) would be good. Don't commercial divers use SCR in very deep situations? At the risk of adding more complication we could have a front mounted counter lung, and some sort of pSCR system could make the diver a little more margin of safety at extreme depth. Perhaps a MCCR where you plan on using a slightly rich make up gas at depth fed through a pSCR system. Obviously if you have some sort of system where the ADV requires a lot of effort to trigger SCR would be a bad idea. What was the "deep" Russian surplus rebreather the IDA 72, with the split bail out system and a very high performance Reg.

On the BOV issue, I to had a CO2 hit, and the only reason I survived was I knew what I had to do (close the DSV, get the bail out reg in my mouth) and I had read an account of how difficult it was to do this. I bailed out, surfaced, felt like butt for a few hours and bought a BOV the next day.

 

[Naumachos]

One question, the cough at the end of exhalation that is talked about at the beginning of the thread is wanted or induced ?

Could be used as respiratory procedure in extreme dives ?

 

[heyydude]

One question, the cough at the end of exhalation that is talked about at the beginning of the thread is wanted or induced ?

Could be used as respiratory procedure in extreme dives ?

Actually, that's a great question I'd love the Dr's on here to answer:

If you're doing a dive (any dive), and you notice yourself coughing at the end of an exhale, should that make you wonder about hypercapnia?

Might be a good thing to keep in mind...

Kevin.