Why no CO2 detection?

[UWSojourner]

Do any RBs have CO2 detection?

From what I've read they don't. There seem to be small detection devices out there, why nothing adapted to RBs yet?

 

[dive]

Do any RBs have CO2 detection?

From what I've read they don't. There seem to be small detection devices out there, why nothing adapted to RBs yet?

Check out this http://thedecostop.com/forums/showthread.php?t=2278&highlight=CO2+detection

 

[BigJetDriver]

Do any RBs have CO2 detection?

From what I've read they don't. There seem to be small detection devices out there, why nothing adapted to RBs yet?

The U.S. Navy has some extremely good CO2 detection devices. Unfortunately, they require the kind of power coming from generatiors on a nuclear sub.

Ambient Pressure Diving (APD) has produced a device that tracks the reaction front in a scrubber and, while not perfect, should act as a pretty good indication of "time remaining before breakthrough".

Cheers!

Rob

 

[caveseeker7]

Do any RBs have CO2 detection?

From what I've read they don't. There seem to be small detection devices out there, why nothing adapted to RBs yet?

UWS, I just reread the TDS thread whose link was posted above.
Not much has changed yet, I'm afraid.

The two rebreathers announced back then that deploy heat sensors, the APD Evolution and OMG Nemesis, have yet to enter the civilian market. Neither actually measures the CO2 content of the loop, but rather the "temperature front" of the most active sorb as it moves through the scrubber bed, indicating how much of the absorbant has been spent. How that will pick up on channeling still eludes me, so I still consider it an indicator rather than a monitor.

The elusive Infinito does have actual CO2 sensor technology that measures loop content of CO2, but is currently not available to the public and also prohibitively priced for many divers (reportedly around $18,000).

The technology could be available as a complete aftermarket controller system, but how feasible would it be to produce a deco/CO2 integrated controller that would be available for $8,000+ ... .

Micropore, manufacturer of the ExtendAir cartridge, released the following data for it in form of a graph. The CO2 concentration in the loop reaches 0.5% at about 210 minutes. Testing was performed at 40 RMV, 1.35 LPM CO2 injection, 1 ata and 13 degrees C/55.4 degrees F. That's for the Dolphin/Azmuth cartridge, where quite some exhaled gas is vented before the scrubber. And 1 ata is of course nonsense unless you dive in your bath tub.

Maybe the most important post in the thread is the one by Stuart McLean (#28), I wholeheartedly agree with him on that issue.

Handle your absorbant properly, pack your correctly, be vigilant with your pre-dive and pre-breathing, and stay within manufacturers ratings and you shouldn't need a monitor.

For the thousands of dollars you safe over a half-a$$ed indicator, and twice that over an accurate monitor you can buy a lot of sorb and afford not to exceed the manufacturer's ratings.

 

[pipedope]

I seem to remember Tom Rose having something in the pipeline but haven't seen any word lately.

It is easy to monitor O2 because it reacts well and is a significant percentage of the gas in the loop. CO2 doesn't react much and it only takes a very small amount to cause trouble. This makes monitoring much harder.

As a diver you really don't care how much CO2 is in the loop as long as it is low enough. It is not like O2 where you always want to know your PPO2.

 

[caveseeker7]

Ambient Pressure Diving (APD) has produced a device that tracks the reaction front in a scrubber and, while not perfect, should act as a pretty good indication of "time remaining before breakthrough".

Maybe, just maybe, a "pretty good indication", but what is that?
What is that to you?
To me it is nothing, really.
It does not detect the actual amount of CO2 in the loop.
It does not recognize channeling through the absorbant.
It does not recognize increased breathing that may lead to decreased dwell times and partially unfiltered gas exiting the scrubber bed.
All it is is an indicator of the process, not an indicator of the result, and an unreliable one at that. Just a warmed up idea served fresh after two decades.

What is the likely chance it will be to some divers?
An "indicaton of time remaining before breakthrough", without the "pretty good" part which to me translates into pretty meaningless. Plenty of divers are already pushing their scrubbers way past their ratings, the last thing they need is any sort of "encouragement" from a pretty good indicator. And more will likely do so from false sense of security in combination with complacency.

 

[dirt diver]

I researched the heck out of it a couple of years ago, and finally gave up. There aren't any sensors that I find that would guarantee to would work well at high ambient pressure and high humidity. The most likely candidate measured one of the infrared absorption bands that CO2 is prominent in, but it's muddied with high humidity. The absolute cheapest I could make something for production would be around 500USD, and most folks would rather just dump their scrubber at X hours. I wasn't planning on a gauge, just an audible alert to signal breakthrough / saturation / flooding. It wasn't worth the time and $$ to investigate further, due to the uncertainty of what the sensor would do in high humidity. Worst case, it might not have registered at all.

There's some interesting new technologies coming out of Europe, but I haven't seen any yet that were specific for CO2 in an O2/N2/He atmosphere.