co2 and computers

uwenthusiast

Forward: recently OW Certified, not a Rebreather diver.

I've read a moderate amount of the accident reports posted on this forum, as well as some of the technical information regarding rebreather operation from other resources in the past. Pretty interesting and I hope to try it after I build OC skills.

It is my understanding from the wikipedia entry that there is no "cell" or sensor that is useful for detection of CO2 in rebreathers at this point in time. It seems as if being able to detect this could add another layer of safety beyond redundant O2 sensors.

My quesiton is this, is there any non-electronic means of detecting CO2 in the levels of a rebreather? Something like a litmus paper that changes colors?

My line of thinking follows. The O2 sensors are most likely read by a ADC (Analog to Digital Converter) that feeds the microcontroller(s). While not natively computer friendly, if there was something like a litmus paper that changes color it could be placed after the scrubber to detect CO2. A small setup using a white-light LED, the litmus paper and a CCD pickup could be made into a small module. The CCD could be sampled by a low-power, USB-host capable microcontroller. The RGB color values would be processed from the CCD module, and the results as to the color of the litmus paper reported if the light source is bad or if the paper changes color.

Perhaps there is no way to detect CO2 within the range that would be useful in a rebreather, but I thought I read somewhere that one of the old scubber materials changed colors as it lost effectiveness.

The whole water threat would still be an issue, as well as condensation on the CCD lens. Perhaps it would gradually change color over the course of the dive. All this besides the whole issue if such a test for CO2 exists.

Thought I would ping for opinions and offer up my hack of a possible detection method up for the crowd.

Def

I just stick a Conairy in my CL and when it stops making noice I start to panic ...

Sorry ... this should be a serious reply, I will shut the door as I leave.

decoweenie

What the heck is it ?

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"...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..."

- Rebreather World PM

edster

Possibly a canary ?

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CCR900

Not just a Conairy but a noicy Conairy

With regards to CO2 detection, I note two makes of CCR now incorporate a heat sensor in or next to the stack. Given such a small value of CO2 can do so much harm maybe monitoring the filter performance is a better way to go.

F

nigelh

We talk about it lot but there isn't anything cost effective there yet and, for all it's dangers, CO2 is a managable problem. Water is a problem, divers drown, but we cope.

Instrumentation is my business and I haven't seen anything yet I'd trust in a real diving enviroment and certainly nothing as cost effective as simply packing the scrubber properly.

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nigelh

zbskii

There's several fairly inexpensive ways of chemically detecting co2. I was thinking this might be a good alternative to an eletronic sensor. Perhaps just a little window or something that turned red when co2 levels got to a dangerous level. It would be a consumable, but then again it should get used every dive, only in an emergency.

nigelh

The suggestion I liked when I heard it was block of scrubber material apres main scrubber with temperature sensors in it so that if it starts to react you know there is CO2 coming through the main block.

The main problem is that it is only very small amounts of CO2 we are talking about. Virtually any CO2 is a bad sign and 0.04bar is just over 0.5% at 60 meters down and that is way too late. Although a CO2 alarm would be nice nobody would pay lots of money or expend lots of effort as we manage the problem quite well.

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nigelh