CO2 build up during 65m (210 ft) dive.

[Teleopsis]

Hi
Thanks for sharing but I am a bit annoyed by your conclusions.
Indeed, aren't these points normal and obvious procedures?
Do you mean that GUE doesn't ingrain the obvious?!

The GUE assembly checklist includes scrubber with <200 minutes on it... although the notes for CCR1 do say "new tech dive, new scrubber simplifies things".

 

[doctormike]

Did you overbreath the scruber or just the physiology of your lungs and wear yourself out?

Not sure if you are asking me or @beester , but this was definitely something different.

I'm in pretty good shape for a 60 year old, I do Peloton almost every day, etc... And I know when I'm getting winded. So the sensation of getting winded I ascribe to the hard work of trying to hold position with a big DSLR in a brisk current and get data. I got out of the current and stopped finning, and felt better pretty quickly.

The headache was new, and since it came on right after this event, I do think that it was CO2 related. And putting everything together - shallow dive, scrubber less than half used, water that was chilly (50F) but not Newfoundland brisk, and the abovementioned exertion - I thought it was safe to stay on the loop.

 

[fsardone]

Well,
kind of proof that what was discussed here
Why depth has an effect on sorb capability to scrub CO2
actually happens.

 

[beester]

Hi
Thanks for sharing but I am a bit annoyed by your conclusions.
Indeed, aren't these points normal and obvious procedures?
Do you mean that GUE doesn't ingrain the obvious?!

The purpose of this forum is to share experiences and info related to diving. Which is what I'm doing. Yes I'm reasonably sure what happened but still it's good to share and get 2nd opinions.

I have no idea why you are bringing GUE into this? GUE has one of the most stringent pre dive checks on rebreathers that exist. One of the checks is regarding scrubber time which should not exceed the CE norm for the unit (which is 200 min).

I've done numerous dives exceeding the 200min CE approved scrubber time on the unit and for these kind of dives so far it seemed totally feasible to use the scrubber up to 300 min. I might need to evaluate this for specific dives and renew the scrubber (as I already said), but your attitude is not helping.

Have you ever had a dive related accident or incident my friend? Evaluating with hindsight is always easy and you are basically not contributing anything.

 

[beester]

Well,
kind of proof that what was discussed here
Why depth has an effect on sorb capability to scrub CO2
actually happens.

Heya fsardone: I scrolled through the topic but I didn't get an end conclusion. Of course temp has an impact on scrubber performance, and depth too. What effect which has in the total performance seems not clear.

My longest 1 dive on the JJ on a new scrubber has exceeded the 200' limit just (3,5 hour deep dive), but I know people who regularly do 5 to 6 hour dives on the unit on a single dive. I've done quite a lot of dives up to 5h scrubber time on the unit. But only if the majority of the dive was in reasonably warm water (deco time/temp vs bottom time/temp) and not exceeding 70m. This is than typically 2 dives before renewing the scrubber. If it's a dive deeper than 70m I've always renewed the scrubber for every dive.

I'm not sure that my case was really a scrubber failing/breakthrough because after a diluent flush and slowing down my breathing the scrubber kept functioning fine for another 15 min on the bottom and then the subsequent 2h of deco. I've always thought that in a real breakthrough of the scrubber you will not be able to stop CO2 build up in the loop (even with frequent diluent flushes)?

Anyway I'm not advocating to use the scrubber over the CE tested limits. I'm also reevaluating my limits on this, because frankly speaking refilling scrubber is not a big task and better safe than sorry.

 

[Jack Hammer]

@beester, I had two incidents with similar feelings on my JJ over the last few years. One I was at about 150'/45m and felt like I wasnt getting enough air, breathing harder and faster than normal. Short version is the the dump cord on the exhale counterlung had got pinched by my can and was being held open enough to slowly leak air from the loop. The other time a combo of my 02 high pressure line shifting just right with my suit inflation bottle being a tad high caused the inhale counterlung volume to be restricted. Both times it started slowly and subtly got worse til I thought I was either taking a CO2 hit or developing IPE. Both were quickly resolved during the dive by checking all gear and tracing my hands over everything.

 

[beester]

Thanks for the write up Jack! What is IPE?

 

[Brad_Horn]

Case: During a 65m (210ft) dive, working on removing some netting, I started to feel CO2 build up up to a point where it started to feel uncomfortable and I was deliberating on moving on OC.

Context: GUE deep diving trip. We had previously dived this wreck (italian corvette sunk in WW2) before and were going to dive it again to document the compass house, depth charges, some porcelain plates, beer bottles and also remove netting from the 10 cm gun so we could take more pics.
- Depth: 65m max, avg 63m.
- Exposure: 45 min bottom time, deco planned around 2 hours (18' deeper deco, 45' 21-9 and 55' on O2(6m))
- Rebreather used: JJ in GUE setup (D8,5L backmounted diluent tanks, 3L O2 and 3L Argon/air supplying wing and drysuit), plus 2 stages (50% and O2).
- Gas used: 12/65
- Scrubber: Already used for about 130' on a dive the day before.
- Temp: bottom 12 degrees, from 20m 20 degrees and warmer.
- Scooters used during descend and bottom phase.

Great report; it's never fun to exhaust a scrubber at depth and unfun experiencing diving outside a rebreathers design envelope.

You don't say how deep you'd dived the day prior but figuring on 40m profile dive for the reported 130min, and depending on how hard you'd worked that day/dive, according to the published JJ-CCR testing by QinetiQ for its CE, you'd nearly already started experiencing breakthrough on that first dive!!! Let alone the second dive...
Your safety buffer being diving slightly warmer +8'C than the CE 40m testing and possibly lower workload at depth....
See attached Figure 3-8.

The single 100m profile dive test run in Figure 3-9 seems to be all you have to plan a 65m dive off. Have JJ published any more testing?
Giving a slight depth (35m) and slight temp (8'C) safety buffer to stay inside your rebreathers design envelope. But possibly if you had planned on working hard at depth, not workload buffer....!

Note however the scrubber duration time variation from the 3 tests for the 40m profile (Figure 3-8) that are not reflected in the 100m profile (Figure 3-9) >> as only a single test was conducted. Which might considerably reduce your safe duration diving envelope, if the result shown is an absolute best case...!
Conversely that single test could be a worst case, or somewhere in between... but that's a big gamble!

 

[GF99/99]

- Depth: 65m max, avg 63m.
- Exposure: 45 min bottom time, deco planned around 2 hours (18' deeper deco, 45' 21-9 and 55' on O2(6m))
- Gas used: 12/65
- Scrubber: Already used for about 130' on a dive the day before.
- Temp: bottom 12 degrees, from 20m 20 degrees and warmer.

I am going to assume since you did not mention it were talking about an axial, not radial or ER radial.

Sorry not to sound rude but your asking why you had a potential CO2 breakthrough when your telling everyone you planned a 65m 165 min dive in 12 degree water with 12/65 trimix and a scrubber that already had 130min on it???? Am I understating this correct?

Just a suggestion you might want to read through your JJ manual and check with your certified JJ instructor on what a safe scrubber duration is, especially when your diving in cold water. I doubt your instructor or the manual will suggest over running your scrubber by almost 2hr. and I would bet big money that the reason they tell you not to over run your scrubber is risk of a CO2 hit.

Also little off topic and not that it is any of my business as everyone is free to dive how they want but I think I might reflect on your diving style/diving mentality because having done tons and tons of 65m-70m dives with 45-60min bottom time 120min deco plan sounds very very aggressive especially is cold water. Personally a 65m 45min bottom time dive for me I would have a total run time of about 185min not 165min and that is diving a 50/75 GF. So to get to a 165min RT would be like diving a 50/90. If you never have issues great I'm all for getting out of the water faster but personally I would rather play things a little more conservative. Same goes for your scrubber durations. But like I said everyone is free to dive how they want just some of use are more conservative than others.

Yes you and your friends might get away with over diving your scrubber 20, 50, 200+ times but what about the 1 time when you don't get away with it. Same goes with diving super aggressively, yeah its nice to get out of the water quicker but remember decompression diving is not an exact science and everyone's body is different. Additionally when you start doing 3+ hour trimix decompression dives remember your tissue loading is extremely high and having some contingency scrubber run time for dives like this is something you might want to keep in the back of your mind when dive planning. What happens if you or your dive buddy starts to get join pain on ascent at your 12m stop and now you drop back down and add 60min of deco to your plan. This would now put you 3hr over your scrubber time that is twice the manufactures rating.

Like I said not trying to sound rude but just some things to think about the last thing we all want is to read another accident report. As another rebreather diver I am all for supporting others and trying to keep the sport safe and help it grow as an industry. For along time rebreathers had a bad reputation but with modern training standards and conservative manufacture recommendations and diving practices rebreathers are an extremely safe way to dive.

 

[KevinNM]

Thanks for the write up Jack! What is IPE?

Immersion pulmonary edema.