Importance of CO2 and scrubber life sensors

[GF99/99]

Long wreck dives at normoxic depths. With 2xAL80 the bottleneck will be the scrubber, then the oxygen and finally the bailout.

Once again as mentioned above BO is your issue a 3hr+ normoxic dive (I am assuming when you use the word normoxic your talking in the 40m-60m range) your limiting factor is going to be bailout. 2ea S80's will not be enough gas if your planning 3hr+ dives. You need to plan your BO gas based on the worst case scenario - the end of your bottom time or the furthest penetration point. Additionally there are many different trains of though on BO gas SAC rates but these should be planned accordingly as well for worst case scenario overexertion, stress diver, CO2 hit, etc.

But anyways BO planning is a personal thing. So if you are doing 3hr+ dives then like myself and others have mentioned many units offer larger scrubber options. See my comments above

What unit do you have?

 

[LFMarm]

What unit do you have?

Optima CM with 5 lbs / 2.2 kg scrubber rated for 220 minutes at >70 deg F / >20C

 

[Wibble]

The best tool for scrubber life is a clock. Just keep track of hour many hours of run time you have on the scrubber. Don't exceed the known good capacity of your unit. These sensors just add cost, complexity and reliability failure points to a CCR.

Would that clock adjust for temperature or other factors such as the diver’s build?

The "stated" maximum scrubber times are always going to be based upon "reasonable worst case" workloads, thus will normally be lower than reality.

Ignore breakthroughs or overworking the scrubber which can only be detected using a CO2 monitor. Alas the technology has issues.

Temperature monitoring does work and can indicate roughly where the scrubber front is, albeit with limitations as the reaction needs to heat up the sensor. For rebreathers with two scrubbers in series, the important monitor is when the second scrubber is being consumed, marking that the halfway point has been passed.

It’s strange that temperature monitoring isn’t more common than Revo and AP's Inspiration — are there others?

Revo displays the remaining scrubber as the time left. Interesting to see how long this is when it’s warm or you’re not working (at deco).

 

[jale]

Hi,
To the good points made above, I will add that, in your situation, you must also add the weather factor.
Three hour dive in the sea is sometime a big bet...

 

[DS79]

If you use your Rebreather as I do, which is 2-3 times a week, like other divers are doing recreational dives, a scrubber monitoring is not just a great safety feature but also giving you a lot more scrubber time without compromising on safety. At least this is true with rEvo‘s dual scrubber/ cycling approach.
Sorb is not that cheap any longer.
So I disagree with those of you, saying just using time counting is actually the better approach. Probably, you should use both approaches/ models before making a judgement.
You would never use a car like that (hours until the tank is empty) and obviously, remaining scrubber time is even more fluctuating than your milage on a car (as a result of the known factors like extension level, temperature, depth, age of the material etc) and obviously, contrary to the car example, a failure is much more fatal.

The remaining scrubber time (RMS) algorhythm on the rEvi is in fact very accurate but you have to understand what is going on there and why scrubber time can fall off the cliff sometimes. In essence, you still have to make wise, conservative decisions - as always in Tec diving.
I typically get around 10-12 hrs diving time out of the 2* 1,35kg(2*3pnd) under cold water conditions (4-6C at bottom) and 40-70m max depths without compromising safety since there is always a completely new, unused second scrubber onboard (thanks to the dual scrubber and cycling). Thats 5-6 hrs „backup/ redundancy“ all the time (in reality - RMS actually gives you much less, if your first scrubber breaks thru).
There are things I don‘t like too much on the rEvo but the scrubber approach (RMS+dual scrubber+cycling) is just a very smart concept.

 

[doctormike]

So I disagree with those of you, saying just using time counting is actually the better approach. Probably, you should use both approaches/ models before making a judgement.
You would never use a car like that (hours until the tank is empty) and obviously, remaining scrubber time is even more fluctuating than your milage on a car (as a result of the known factors like extension level, temperature, depth, age of the material etc) and obviously, contrary to the car example, a failure is much more fatal.

I have never used a temp stick, so forgive me if I don't understand the nuances. But the analogy seems off to me.

The CE (or whatever other guidelines) published for scrubber duration are extremely conservative, assuming very cold water and very high workload. I wish that there was published data for my scrubber (JJ) in water temperatures closer to what I usually dive, but there aren't so I stick with the guidelines, realizing that I am wasting sorb. But that's OK.

Assuming that you know how to pack a scrubber and do it correctly, the temp stick is really a way of giving you an assurance that you can run your scrubber longer than rated, right? It's unlikely that you will be in a situation that you are working SO hard that it will tell you to get out of the water when you still have stack time left, right? So it would be more like if your car had a timer based on time to an empty fuel tank, calculated as if you were driving 100 MPH uphill towing a trailer or something. If you follow that, you aren't going to run out of gas with normal driving.

It's pretty clear that many experienced CCR divers, especially those diving in warm water, do routinely run far beyond published duration data, so maybe the temp stick would be more useful for those people?

I had my first CO2 hit two weeks ago, writing that up now. I don't think that a temp stick would have prevented that (sudden increase in workload). A CO2 monitor would have helped, but as mentioned upthread, they aren't really a CCR thing at this point in history.

 

[JonG1]

Does anyone know if @nadwidny experience has been published by DAN yet?

 

[nadwidny]

Does anyone know if @nadwidny experience has been published by DAN yet?

It hasn't.

 

[Tassi Devil Diver]

I had my first CO2 hit two weeks ago, writing that up now. I don't think that a temp stick would have prevented that (sudden increase in workload). A CO2 monitor would have helped, but as mentioned upthread, they aren't really a CCR thing at this point in history.

If your CO2 hit had of been as a result scrubber breakthrough the rEvo RMS would have picked it up and given you warning through rapidly dropping remaining scrubber time.

Your hit sounds like more to do with retained CO2, so the rEvo RMS or any scrubber monitoring system would not have picked it up. Maybe a CO2 monitor measuring end tidal CO2 would have given you warning but that technology is not available in rebreathers.

 

[JonG1]

It hasn't.

Thanks @nadwidny. Did you enjoy Malin, think we were there 2 weeks after you.