Time to recover SAC after CO2 hit

[Mr.Dave]

.... in the case of the breakthrough stayed on just to see how it would play out for the next ten minutes. In all instances I've noticed this as an increased pace of about 30-50% above normal and even before that in a sense that something is wrong.

I've been fortunate enough not to have experienced CO2 breakthrough and so don't have a feeling as to how I'd react / feel / recover (hence reason for post)... For clarification, did you notice the increase in breathing rate then decide to stay on the loop, or another symptom first then after another 10mins on the loop an increase in breathing rate?

I have experienced CO2 retention (task loading + minimum loop volume) which increased my breathing rate considerably and anxiety levels. When I recognised it I stopped what I was doing, concentrated on my breathing and calmed down, ~1-2min before back to normal.

D.

 

[AlexBerger]

I have never had a head on crash in a car so does that mean it dosent hapen?

Ever coughed underwater? Thats about 2 ltrs of air mooving at 50mph in a fraction of a second

What effect do you think that might have on a mushroom valve?

What effect do you think a bit of phlegm would have on a mushroom valve


And that was just one example of a unit failure C02 hit

One diver had a C02 hit after a counterlung tie down failed causing the CL to float up too high and increase his WOB.

so your saying that we better use co2 censors cos its unlikly that a scruber fails but it happens and peopel have died

 

[Johan Isaksson]

I've been fortunate enough not to have experienced CO2 breakthrough and so don't have a feeling as to how I'd react / feel / recover (hence reason for post)... For clarification, did you notice the increase in breathing rate then decide to stay on the loop, or another symptom first then after another 10mins on the loop an increase in breathing rate?

I have experienced CO2 retention (task loading + minimum loop volume) which increased my breathing rate considerably and anxiety levels. When I recognised it I stopped what I was doing, concentrated on my breathing and calmed down, ~1-2min before back to normal.

D.

In that particular case I noticed the increase in breathing rate first and stayed on the loop to finish the dive just to see how I would react. It was cold water and I had pushed the scrubber a bit so cause was likely a partial breakthrough.

 

[Mark Chase]

so your saying that we better use co2 censors cos its unlikly that a scruber fails but it happens and peopel have died

I am not saying anything?

My problem is do C02 monitors do anything besides check for scrubber failure?

If they don't then I dont really see the point because scrubber failure is way way down on my list of issues relating to C02 that I am concerned about


ATB

 

[garethingham]

If you listen to the experts it's all about retained C02. Without end tidal monitoring we are just guessing.


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[AlexBerger]

If you listen to the experts it's all about retained C02. Without end tidal monitoring we are just guessing.


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exactly and one way of retaining co2 one of many is your scruber so what is so wrong about monitoring it? for now that is the best we got, use it or guess

 

[Johan Isaksson]

I personally consider a post-scrubber CO2 detector as a very low priority compared to unit design, sensible dive planning and good packing routines. It only really covers the one failure mode and that failure is the one that worries me the least by far. To me it's simply not worth the added electronics to monitor that side.

There is another option to the end-tidal measurements that I routinely drop into these conversations in the hope that someone would start fiddling around with it and that's transcutaneous monitoring. Basically it's a probe placed on the skin that measures blood CO2 levels. It's in routine use in medicine but there are some technological issues that could present problems. If it works it'd likely be about equal to end-tidal monitoring and could cover hypoxia as well. I have one at work and tried it for a dry run last year just for the heck of it. Far from anything resembling formal testing but it did work at least.

 

[matt]

I personally consider a post-scrubber CO2 detector as a very low priority compared to unit design, sensible dive planning and good packing routines. It only really covers the one failure mode and that failure is the one that worries me the least by far. To me it's simply not worth the added electronics to monitor that side.

There is another option to the end-tidal measurements that I routinely drop into these conversations in the hope that someone would start fiddling around with it and that's transcutaneous monitoring. Basically it's a probe placed on the skin that measures blood CO2 levels. It's in routine use in medicine but there are some technological issues that could present problems. If it works it'd likely be about equal to end-tidal monitoring and could cover hypoxia as well. I have one at work and tried it for a dry run last year just for the heck of it. Far from anything resembling formal testing but it did work at least.

I agree the APD CO2 sensor isn't of much value. It's an all or nothing device that tells you very little about the state of the CO2. It's littered with false-positives too.

I've been using mine to see how good the tempstick is. I'm only doing this is warm, 29c water. Being able to confidently get to the last 2 blocks on the tempstick is useful when travelling.

Matt.

 

[moose_grunt]

Being able to confidently get to the last 2 blocks on the tempstick is useful when travelling.

Matt.

Just curious, but how many hours does that give you?

 

[matt]

Just curious, but how many hours does that give you?

Highly dependent on the water-temperature. Here's the display at 427 mins (7h07). Still one block to go before the first alarm. Water 29c. Sofnolime 797.

Matt.

 

[Vanny]

Matt,

Would you trust the temp stick to that extent in the uk?

Cheers


Edit; sorry I've assumed the 29 degrees wasn't uk, hahahahahaha

 

[matt]

And here's another. This time 570 mins (9h30) to the same point - one block from the alarm. 29.5c, 797.

I did a couple of deeper ones ones on this run: 71, 62, 20, 36, 24, 60, 16, 21m. But no significant deco - just a big wall.

Matt.

 

[matt]

Matt,

Would you trust the temp stick to that extent in the uk?

Cheers


Edit; sorry I've assumed the 29 degrees wasn't uk, hahahahahaha

Yes, I trust the temp-stick as I have used it a lot. In colder water I keep to 3 blocks though.

Here's to 236 mins (3h56) in 15c, Sofnolime 797.

That's to 4 blocks. I would have used that for 1 more dive (short stop), but the next day was 60m so it was replaced.

For UK no stop UK diving I would re-use to 3 blocks, but for long stop gas diving (any temperature) I take a new scrubber.

Matt.

 

[Vanny]

Cheers, interesting.

 

[Robert]

well it dos not but tell me did you have your mushoom valves fail after you predive test them?and dos that happen cos it never did to me

I had one dive where it they might have failed - the cause was vomiting into the loop. I couldn't verify whether the muchroom valves were fully working or partially obstructed by solids in the vomit so I bailed out,

Thanks,
Robert

 

[fsardone]

Hello,
some time ago I was training for my solo which was necessary for extended range Trimix in OC.
During this training there were a couple of exercises with high intensity physical effort (I was in OC with 3 stages and a twinset) and I have got a CO2 hit.
So no rebreather, no scrubber or mushroom valves to fail.

I stopped all activities I was at 12 meters, no deco obbligation and I was looking at the SPG run down. So I surfaced and waited about 15 minutes hanging on the anchor line of the support boat before being able to re-submerge with decent respiratory control. Notwithstanding the experience (I have been diving for 30+ years), my ease with no mask diving after the hit I could not complete the exercises that required me to remove the mask.

Since then I have a very healthy respect for CO2. I then moved to CCR with an increased WOB and all the issues concerning the scrubber (packing building the train) and the loop. My approach is that a CO2 hit HAS to be prevented, I found out is hardly recoverable in OC and shallow. I consider it a killer at depth with any significant deco obligation.

Just my opinion ... but based on first hand experience.
I will always be glad to my instructor that showed me what really means being out of breath at depth, and that was not even close to the flight or fight instinct when I decided (I was still in control of my mind) to surface.

Cheers

Fabio

 

[Mark Chase]

exactly and one way of retaining co2 one of many is your scruber so what is so wrong about monitoring it? for now that is the best we got, use it or guess

Retained C02 has nothing to do with your scrubber

The only influance your scrubber could have is increasing the WOB due to being wet

 

[AlexBerger]

Retained C02 has nothing to do with your scrubber

The only influance your scrubber could have is increasing the WOB due to being wet

so if your scruber fails for any reason you will retain co2 yes?

 

[matt]

so if your scruber fails for any reason you will retain co2 yes?

Yes, I think this is right - any elevation of CO2 (hypercapnia) is described as CO2 retention.

CO2 retention can occur either due to elevated CO2 in the breathing gas (by-pass, etc.) or because of inadequate ventilation. When CO2 rises the brain normally causes ventilation to increase (sub-consciously) to clear the excess CO2. Retention which comes about due to inadequate ventilation isn't anything to do with breakthrough of the scrubber, and wouldn't be detected by the post-scrubber sensor.

It seems that the act of scuba-diving can alter the way the brain works and in some people elevated work-of-breathing due to things like gas-density, depth, equipment-choices, hard-work, etc. can cause CO2 to be retained. CO2 retained in this way is often differentiated in forum-diving-circles from scrubber-breakthrough and I think that is the distinction Mark is alluding to.

CO2 retention due to inadequate ventilation isn't anything to do with the scrubber, and even occurs OC. Some people, called CO2-retainers, are able to tolerate elevated CO2 levels without experiencing the initial symptom of hypercapnia. This is another use of that term.

I'm not an expert, but that is how I understand it. Sorry if this isn't useful to you.

Matt.

 

[Mark Chase]

so if your scruber fails for any reason you will retain co2 yes?

NO


If your scruber fails you will breath C02

If you retain C02 it is due to a work of breathiung issue causeing a colaps of the avoli in the lungs which will not alow you to properly exhale the C02 YOUR BODY PRODUCES

This can occur on a perfictly packed brand new scrubber

And a C02 scrubber moniter temp stick or RMS device will not detect it

IMHO retained WOB, skip cycle, short sharp or over breathing related C02 issues or equipment failure related C02 issues are more likley to be an issue that scrubber related ones

As seen above you can push a standard inspo scrubber to 10 hours. Personaly I dont go past 6.

Using a C02 monitor on a Inspo sized scrubber when your doing 3 hours max is only catching badly packed scrubbers. Argubly it will also catch faulty lime? but how often does that happen?

The way I pack my scrubber is very repeatable. SOme say its not the best way but I have a ot of hours often under some prety harsh conditions, so I have built up confidance that whilst it might not be the best, it seems to be safe.

C02 monitors and scrubber monitors are IMHO just a way for divers to push the limits on a scrubber. They dont deel with unit failure or retained C02 so I see them as of little benifit in that area.

If it came free with the unit I wouldent take it off but equaly I wouldent spend extra money buying one.

IF they ever produce an End tidal C02 system thats reliable and functional, I would consider one.

ATB