CO - how high will you go?

[Bombay High]

Tests were conducted on Saturation divers living in enclosed hyperbaric environments for a long period of time.
Since CO is a gas that humans excrete with every exhalation, albeit in very small quantities, it was studied to see how much this increases in the course of a deep Saturation dive typically lasting about 30 days including decompression.
It was found that by day 8 or 9 CO levels had reached a level where it impeded the divers performance.

If I remember right, this led to Sofnacat being used in Sat complexes to remove CO build up.

 

[copter53]

Is this a tech dive only concern or is it a hazard for rec open circuit divers as well?

 

[DandyDon]

Is this a tech dive only concern or is it a hazard for rec open circuit divers as well?

You don't want it in your tank on any dive. I posted a link to my article above.

 

[moody s]

Is this a tech dive only concern or is it a hazard for rec open circuit divers as well?

Everyone, I'd say more so recreational divers as they are less likely to have there own tanks or be concerned about their breathing gas. Sometimes as a rec diver you don't know what tanks you are breathing from till you are on the boat.

 

[Jax]

From my googling (I'm not qualified to give an official answer) I find references that Modified Grade E standard is < 2ppm. Web pages suggest any reading over 1.5 should be investigated.

I think 3ppm is the max allowed in Australia. I suspect he needs to change his compressor oil and use the more expensive synthetic as hot compressors can produce CO internally. https://www.breathingair.com/products/oil-compressor-synthetic They also sell compressor oil for less than half as much, and I suspect that most get it.

Testing tank after tank at 0 ppm can get boring but the first time you read a reading is kind of exciting huh? Thanks for sharing the experience.

View attachment 160020

It looks like 10 ppm of CO is the most common standard, with 20 ppm being used by the US Navy.

I think there may be some apples and oranges mixed here.

Alarms go off at 10ppm in air at normal (i.e., sea level) pressure.


However, when you dive breathing gas contaminated by CO, the CO partial pressure increases just like all the other gas partial pressures.

Therefore, diving with air contaminated at 3ppm in normal 1ATM, but you're going down to 3 or 4 ATM, your CO is denser per liter / sq in as is all parts of air, and you can quickly become poisoned.


Is my reasoning correct?

 

[DandyDon]

I think there may be some apples and oranges mixed here.

Alarms go off at 10ppm in air at normal (i.e., sea level) pressure.


However, when you dive breathing gas contaminated by CO, the CO partial pressure increases just like all the other gas partial pressures.

Therefore, diving with air contaminated at 3ppm in normal 1ATM, but you're going down to 3 or 4 ATM, your CO is denser per liter / sq in as is all parts of air, and you can quickly become poisoned.


Is my reasoning correct?

Oh 10-20 ppm is nothing at sea level. At depth with partial pressure increase as you mentioned concentrates the effect and much more as we've been discussing.

Most countries do not have regulations, but for the US the max is 10 ppm in tank air, in other countries from 3 to 15 ppm, and for personal calls - pick a number. 3 ppm seems kinda picky to some, but then there should be none in there anyway - and if they allow that much, what else is getting by?

Testing in ppm was the original challenge, but now we have the technology. If you calibrate your tester correctly, like with the Analox - adjust the knob in seemingly clean air, then I'd still take a 1 or a 2 as a false positive. I start complaining at 3 but have knowingly dived tanks up to 5.

 

[dfx]

I think there may be some apples and oranges mixed here.

Alarms go off at 10ppm in air at normal (i.e., sea level) pressure.


However, when you dive breathing gas contaminated by CO, the CO partial pressure increases just like all the other gas partial pressures.

Therefore, diving with air contaminated at 3ppm in normal 1ATM, but you're going down to 3 or 4 ATM, your CO is denser per liter / sq in as is all parts of air, and you can quickly become poisoned.


Is my reasoning correct?

Yes and no.

"ppm" is parts per million. It's the number of molecules in relation to the number of molecules (or mass in relation to mass, or moles in relation to moles, etc). It doesn't change with changes in pressure. 10 ppm at 1 atm will still be 10 ppm at 3 atm.

Other than this technicality, you're right. However, I don't know what's physiologically significant... Actual ppm or the partial pressure equivalent.

 

[chrpai]

Atmosphere of Earth - Wikipedia, the free encyclopedia

Nitrogen (N2) 780,840 ppmv (78.084%)
Oxygen (O2) 209,460 ppmv (20.946%)
Argon (Ar) 9,340 ppmv (0.9340%)
Carbon dioxide (CO2) 397 ppmv (0.0397%)
Neon (Ne) 18.18 ppmv (0.001818%)
Helium (He) 5.24 ppmv (0.000524%)
Methane (CH4) 1.79 ppmv (0.000179%)
Krypton (Kr) 1.14 ppmv (0.000114%)
Hydrogen (H2) 0.55 ppmv (0.000055%)
Nitrous oxide (N2O) 0.325 ppmv (0.0000325%)
Carbon monoxide (CO) 0.1 ppmv (0.00001%)

In this context, 2ppm would be 20x normal.

 

[DandyDon]

Atmosphere of Earth - Wikipedia, the free encyclopedia

Nitrogen (N2) 780,840 ppmv (78.084%)
Oxygen (O2) 209,460 ppmv (20.946%)
Argon (Ar) 9,340 ppmv (0.9340%)
Carbon dioxide (CO2) 397 ppmv (0.0397%)
Neon (Ne) 18.18 ppmv (0.001818%)
Helium (He) 5.24 ppmv (0.000524%)
Methane (CH4) 1.79 ppmv (0.000179%)
Krypton (Kr) 1.14 ppmv (0.000114%)
Hydrogen (H2) 0.55 ppmv (0.000055%)
Nitrous oxide (N2O) 0.325 ppmv (0.0000325%)
Carbon monoxide (CO) 0.1 ppmv (0.00001%)

In this context, 2ppm would be 20x normal.

Well, if you compare to the whole atmosphere, all layers, but that really is comparing watermelons to kumquats. I think in the lower elevations of the troposphere, the average is much higher. Clean, country air with no smoke can be assumed at effectively 0 ppm for our calibration purposes, but Cedar Park & Austin at rush hour could easily run 5 ppm, altho the average level for Austin is considered under 1 ppm. http://www.usa.com/austin-tx-air-quality.htm#epaaqi

Inside a home with gas heating, cooking, or water heating, a fireplace, a smoker, etc. over 5 ppm is common. Keeping CO alarms armed and tested is important, and annual inspections are suggested.

 

[Scared Silly]

View attachment 160020

It looks like 10 ppm of CO is the most common standard, with 20 ppm being used by the US Navy.

Other than ANDI and the nitrox it is not clear to me if these standards are for diving as compressed air is used by firemen.


The issue of CO at depth is the partial pressure coupled with bind affinity. I do not know all of the physiology.