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

[Valyngar]

I do 2x 2,5 hour dives to 45-60 meters regulary on cold 4 degree water on same scrubber without any co2 problems. This is also common custom here. Some guys do even up to 8 hour dives with it. I don't think your scrubber usage was main point why you got co2 hit. I have had co2 build up in 5 meters when working hard after just 2 hours usage. Same with new scrubber when just diving hard on ~15meters. So I would more put this on working hard than using spend scrubber.

 

[fsardone]

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.

Hello Beester,
the problem here is that the reaction front deepens with increased gas density and efficiency lowers.
So the scrubber is not able to keep up with:
-increased flow;
-increased rate of production of CO2
Lowering them makes a scrubber able to cope but you are endangering yourself.
I dive inspiration.
The manual says scrubber duration 180 but:
Depth less than 50 mt after 100 minutes
Depth less than 20 mt after 140 minutes
so the last 40 minutes should be done between 20 and surface.

Bottom line is deep dive new scrubber. Is 10 euros of cat litter in exchenge of peace of mind.

Cheers

Fabio

 

[beester]

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!

I know this report. The key however is the water temp and the respiratory volume per minute (40L/min). How much this matters is of course up to debate, but 40L/min is an unsustainable breathing rate even for 30 minutes let alone 180 min.

 

[Brad_Horn]

I know this report. The key however is the water temp and the respiratory volume per minute (40L/min). How much this matters is of course up to debate, but 40L/min is an unsustainable breathing rate even for 30 minutes let alone 180 min.

See also Ireland | John Clarke Online

 

[jale]

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.

Hi Beester.
Sorry if you feel my tone wasn't nice but it was not my intention.
As I said, I applaud you to bring this problem and we are here indeed to learn from each other.
I did of course had accidents and unfortunately even went to a chamber.
The reference to GUE was from you (GUE dive, GUE set-up) and for me, it was meant to be as a ironic comment because it seems that every times a negative connotation is made against GUE, it is perceived as sacrilegious.
Really nothing against you and your report is really a good way to pounder a bit more how we can try to react in the best way when we have problems underwater. Thanks.

 

[Brad_Horn]

I'd be having a good look at the mushroom valves

That has only been identified as a measurable factor at 100m. See attached.

Unknown if it presents enough of a problem or is even measurable at 65m.....

 

[beester]

View attachment 734166

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.

Ok me addressing your different points will be a bit here and there but let me try.

Decompression:
The topic is not decompression but scrubber use, procedures, and sharing experiences. It's funny you are starting to break down a decompression plan, while I haven't given ANY real details on our plans. Next I've done over 200 trimix dives in this range (and deeper) diving anything from 20/90 to 50/70 (GF) and with deco times up to 3 hours and so far it's working out fine. (touch of wood). Like I say I'm happy to share experiences on deco profiles but PM me, because that's OT.

Emergency/extra deco time and scrubber use:
We calculate having to add deco time on the scrubber. However it's deco time, meaning spend in the shallow warm water where the scrubber duration/performance is much higher. I haven't seen anyone get a hit at the 18-15 m stop (I've heard about them for sure, but these are different profiles (+120-140m dives)), yes ascending from 12 to 9 and from 9 to 6 i've seen, but we would not descend again in this scenario for the full deco profile, just descend 1 deco step and redo the deco at that depth before moving up again. We also almost always use scooters so there is no workload during the ascend (swimming against current etc). Finally we carry a lot of bailout per diver (no team bailout planned), typically a ful 80cuft tank more than typical rebreather divers.

Scubber limits and practical use:
Regarding your scrubber comments I get your concern (although I don't really like your tone, implying I'm a goof who's not read the manual or taken propper classes). That's why I'm posting here (and getting pummeled by some of you ;-) ). I will probably change the process and start using a new scrubber for any single dive deeper than 50m/runtime over 2 hours to create extra safety margin. However stating that anything over the CE 180' scrubber usage is a death sentence is also widely off the mark. The point is that on a typical dive like this the average depth post dive is in the 23-28m range, you will spend 70 percent of the time in shallow warm water (20 degrees plus) and your workload will be minimal. How far that limit goes is a big unknown and it's better to be safe than sorry I understand that.

Would be interesting to know how many JJ divers doing deeper dives exceed the 180' limit on scrubber time (or because the runtime of 1 dive is longer or because they do multiple dives on the unit). Same goes for other rebreathers of course... maybe we should make a poll.

 

[beester]

Hi Beester.
Sorry if you feel my tone wasn't nice but it was not my intention.
As I said, I applaud you to bring this problem and we are here indeed to learn from each other.
I did of course had accidents and unfortunately even went to a chamber.
The reference to GUE was from you (GUE dive, GUE set-up) and for me, it was meant to be as a ironic comment because it seems that every times a negative connotation is made against GUE, it is perceived as sacrilegious.
Really nothing against you and your report is really a good way to pounder a bit more how we can try to react in the best way when we have problems underwater. Thanks.

No worries, maybe I am a bit too sensitive and could use a beer in this heat ;-) The problem is that if a PADI/TDI/IANTD diver (fill in whatever organisation you want) does something goofy, off the norm or plain stupid, nobody is going to immediately start looking at the organisation. Unless it's a clear case of the procedures/training/limits of the organisation being goofy, off the norm or plain stupid.

With GUE it's never the case. You get a lot of comments focussing immediately on GUE, while in most cases that's not relevant. I only mentioned GUE to give a bit of context nothing more.

Like I say it's not because I'm a goofball that the whole GUE community is. Anyway cheers ;-)

 

[Heat Miser]

- Bail out sooner rather than later. In fact CO2 build up is one of the only real reasons to quickly bail out at depth (the other being super low PPO2).

Isn't there a third reason to bail out -- Super high PPO2?

thanks for sharing.

 

[broncobowsher]

Used scrubber, deep, cold. All factors but none should be an issue.
Heavy work load in those conditions, I think that is the factor that is overlooked. Easy enough to be a tourist and looking at things. But working hard, using a lot of energy, producing a lot of CO2, heavy breathing. Think getting winded working out on the surface and combine that with being on a rebreather at depth. Might not be working that hard, but there is a lot of other stuff going on to add to it (mainly being on a rebreather at depth)