Question from a Rebreather ignorant person

[Couv]

Whilst climbing the stairs of the Ivory Tower today, I was contemplating the gentleman's dilemma in the video posted in another thread. It got me wondering if CCRs are equipped with CO2 sensors. If not, would the addition of such a sensor be of use in order to give an early warning of eminent hypercapnia due to elevated CO2 or would this be just another expensive annoyance?

Please keep in mind I am rebreather ignorant so talk slowly and gently.

Thank you,

couv

 

[wedivebc]

Whilst climbing the stairs of the Ivory Tower today, I was contemplating the gentleman's dilemma in the video posted in another thread. It got me wondering if CCRs are equipped with CO2 sensors. If not, would the addition of such a sensor be of use in order to give an early warning of eminent hypercapnia due to elevated CO2 or would this be just another expensive annoyance?

Please keep in mind I am rebreather ignorant so talk slowly and gently.

Thank you,

couv

A CO2 sensor is a technology that is just out of reach of the rebreather community right now. There are CO2 sensors used in medicine and industry but for sport diving there are still some technological difficulties to overcome. One of the main problems is the sensors inabilty to work in a damp environment. It will happen but does not look like anytime soon

 

[mania]

I think the whole community waits for it. Unfortunately it's not in the foreseeing future.

Mania

 

[futuredsd44]

First off I'm not a rebreather diver yet, but I read somewhere I think it was diveriteexpress.com that the level of CO2 you breath out would interfere with any kind of sensor that could be placed in the breathing loop, and they haven't found a way around this yet.

 

[Meng_Tze]

I can see how exhaled CO2 could skew total volume of CO2 in a closed system yes. If this is a real problem or just an engineering challenge, not sure.

 

[Tienuts]

I recall reading somewhere, that current CO2 sensors have a large current draw - too large to be practical, and also the response time is upwards of 60 seconds. If that is the case, by the time it alarmed, you'd be dead.

 

[djcheburashka]

The problem is actually a little bit different. Viable CO2 censors are not hard to make, and don't require too much power to run.

The problem is that the amount of CO2 in air is incredibly small -- on the order of 400 parts per million. And the point at which CO2 starts to become dangerous -- about 1000 ppm or 0.1% on the surface -- is very small too. If you compare that to O2 sensors, they generally have to deal with a range of 10 to 100%, partial pressures of 0.1 to 2.0 (if you're in trouble) or so. And they're accurate to, what, 0.01 atm? You can see that a CO2 meter would have to be much more sensitive and accurate to be of any value.

Building a CO2 detector that is both sensitive enough and accurate enough to handle that, while being small and energy efficient and reliable enough for diving, that is the challenge.

 

[wedivebc]

And the point at which CO2 starts to become dangerous -- about 1000 ppm or 0.1% on the surface -- is very small too.

I think your figures are way off. 10 times that amount is barely detectable by most people.
Don't forget we expell 3-4% CO2 with every breath. 10% CO2 is dangerous.

 

[Gill Envy]

the way that it's been explained to me is that co2 is so toxic and the amount needed to incapacitate is so small that the time from breakthrough to the time you become incapacitated is too short to make a monitor that helpful. One thing I really liked about the evolution was the temp stick, seems like knowing how close to spent the scrubber is before co2 is likely to get into the inhale side of the loop is much more useful. Prevention is key. Once it's detectible it's basically too late.

at least that's how it's been explained to me.

 

[Jeff Toorish]

I think we will see a practical CO2 sensor for rebreathers within the next couple of years.

Jeff