wstorms
Contributor
Hi all,
I am wondering about the sense / nonsense of CO monitoring. Obviously CO in your gas is bad, but at what value? When would you breath a gas and when wouldn't you? I tried to come up with it myself, but the extremely tight tolerances puzzle me:
- CO is natural, 5-10 ppm isn't unusual. Low concentration like that (at atmospheric pressure) is ok
- at depth however, the same concentration can become a problem, so it's a good idea to filter as much as possible (all clear so far)
- ANDI defines 2 ppm CO as the max for a breathing gas (I haven't found other norms from other agencies), so I am considering 2 ppm as the max safe amount
- Even CO sensors specifically for diving purposes like the DE- OX SAFE have tolerances of 2-4 ppm or more, so potentially twice the max level. A deviation +/- 1% isn't unusual
- sensors are usually least reliable at the extreme ends of the scale, so there is even extra uncertainty if you want to measure so close to 0 ppm
So it would easily be possible to have 4 ppm in your actual gas, but still measuring 0 ppm. If you can have double the maximum amount of CO, but still have a "safe" reading, how valuable is the measurement? Do you simply consider a reading of any CO as a "no go" for the gas?
I am wondering about the sense / nonsense of CO monitoring. Obviously CO in your gas is bad, but at what value? When would you breath a gas and when wouldn't you? I tried to come up with it myself, but the extremely tight tolerances puzzle me:
- CO is natural, 5-10 ppm isn't unusual. Low concentration like that (at atmospheric pressure) is ok
- at depth however, the same concentration can become a problem, so it's a good idea to filter as much as possible (all clear so far)
- ANDI defines 2 ppm CO as the max for a breathing gas (I haven't found other norms from other agencies), so I am considering 2 ppm as the max safe amount
- Even CO sensors specifically for diving purposes like the DE- OX SAFE have tolerances of 2-4 ppm or more, so potentially twice the max level. A deviation +/- 1% isn't unusual
- sensors are usually least reliable at the extreme ends of the scale, so there is even extra uncertainty if you want to measure so close to 0 ppm
So it would easily be possible to have 4 ppm in your actual gas, but still measuring 0 ppm. If you can have double the maximum amount of CO, but still have a "safe" reading, how valuable is the measurement? Do you simply consider a reading of any CO as a "no go" for the gas?