How much CO2 is too much?

E-man

So what CO2 percentage in the loop would be considered too much?

caveseeker7

The limit for CO2 in the loop, as applied for rating the scrubber duration under CE and various military test standards is 0.5% SEV (surface equivalent value), or 5000 ppm (parts per million).

__________________
Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.'!"

MikeH

IIRC, 0.5% CO2 or greater is concidered too much.

Mike

E-man

I was curious if anyone had any knowledge of breathing on CO2 higher than the 0.5% limit.

caveseeker7

I'm pretty sure there is info on that, just don't know if or where it's available.
USN standard used to be 1.0% SEV CO2 in the loop, and machine testing was done to 2.5% SEV CO2 if I remeber correctly. They probably did manned testing, too., it's the Experimental Diving Unit after all.

Maybe some of the docs can point you in the right direction.

__________________
Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.'!"

abowie

In what regard?

I've breathed carbogen (5%CO2 in 95% O2) during a physiology practical as a medical student. It makes you feel a bit short of breath. The longer you breathe it the more SOB you get. It wasn't pleasant.

I recently breathed pure CO2 at 6l via an open "Hudson" mask (probably giving me 30% or more inspired CO2). I found this cylinder sitting in the cardiac surgery theatre at one of the hospitals I work in and thought "I wonder what that's like to breathe?".

Idiot! It was horrible. After 2 deep breaths I felt dizzy, horribly short of breath and it tasted terrible.

To be honest, breathing 0.5% CO2 (3.7mmHg partial pressure) at sea level won't do you any harm at all, but that's not the point.

Any CO2 in the inspired limb of your Rebreather circuit indicates failure (either static or dynamic) of the scrubber mechanism. Breathing it at depth increases the partial pressure and the problems you're going to have.

NO CO2 in the inspired limb is what you want at all times.

Changing the subject, breathing a hypoxic mix will make you SOB as well.

Flying back home from Bikini a couple of weeks ago we left in an unpressurised little flying shitbox belonging to Marshall Air. I could tell it was unpressurised because I could see daylight around the door seal.

My VR3 said air pressure was 713mBar which made me feel great after a week of 2 deco dives per day. I calculated that that was the equivalent of breathing 14.7% O2 at sea level, and that my alveolar PO2 was about 56mmHg (less than 90% Hb/O2 saturation; normal would be close to 100mmHg).

I felt moderately SOB.

__________________
Andrew Bowie

Rebreather-friendly Buddy

MikeH

713mb is approximately 10,000ft(~3000m), give or take 1000ft. You were probably on a Twin Otter out of Bikini.

Mike

dteubner

I found this great altitude/barometric pressure table yesterday http://www.sablesys.com/baro-altitude.html

I have also written a spreadsheet about the alveolar gas equation which calculates what the alveolar oxygen content is from ambient pressure, FI02 etc. There is also a page which shows arterial oxygen tensions with degrees of low O2 inspired gas with various CO2 levels - http://www.davidteubner.com/images/A...20equation.xls

Dave T

MikeH

Take a look at the chart again. The number that you are looking at, which shows 719.6 at 1500 feet, is mm of Mercury absolute(mm Hg Abs)....NOT millibars, which is what the VR3 measures in.

On that chart, to get millibars, take the last column(kPa A) and move the decimal point one to the right. For instance - Sea level pressure is 103.3 kPa, and 1013.3 mb.

For accurate conversions, use http://www.onlineconversion.com/pressure.htm ..

Mike

Underwaterbear

...or you could just remember that over the first 10 000 feet atmospheric pressure lapse rate is about 32 millibars / 1000 ft.

If they were heading from Bikini to Majuro, technically the aircraft should have been flying at 9500 ft since the flight is south east...but who knows what they do out there