[The_blue]

Right we were doing an old sport diver test last night and it came to the old 'whats the PP of co2 at 30m' question.

Now i know the answer is .04 bar but.......


we got onto the subject of O2PP and exhailed gas and knowing that we breath out 16% O2.

At 20m the PP of air in is aprox .6bar O2 and 2.4 bar Nitrogen.

so would air breathed out be

.56 bar O2 , .04 bar co2 and 2.4 nitrogen?

cos i'm reconing that .16bar x 20m= .48 dosn't sound right.

 

[chrisch]

... knowing that we breath out 16% O2.

...

Only at the surface

Go figure.

Chris

 

[5363]

.56 bar O2 , .04 bar co2 and 2.4 nitrogen?

Yes


When you metabolise food, you produce a certain amount of CO2. Assuming you're not excercising any more at depth, the number of CO2 molecules you produce is exactly the same at 20m as at the surface and the total amount of O2 you use up is the same, but at 20m there are 3 times as many O2 molecules in each breath. Therefore that small amount of CO2 is now exhaled in 3 times as many gas molecules and will be diluted by a factor of 3.

 

[Brick]

Presuming that your body is using oxygen at the same rate, you'll be breathing out a much higher percentage of O2 than you would at the surface.

 

[MixedUp]

Presuming that your body is using oxygen at the same rate, you'll be breathing out a much higher percentage of O2 than you would at the surface.

Breathing out??? just think of the waste with all those bubbles, get a rebreather.

Steve

 

[Brick]

I know - it almost makes me cry to see all that useful gas happily drifting up to the surface unused. You pay for it then only use a tiny fraction of it - what a waste! Thankfully, with my new job, I'll be able to finally afford a breather so no more waste!

 

[chrisch]

I know - it almost makes me cry to see all that useful gas happily drifting up to the surface unused. ...

Yeah, but the fish love it.

Chris

 

[The_blue]

Thanks folk.

Knew i was right

 

[nigelH]

Right we were doing an old sport diver test last night and it came to the old 'whats the PP of co2 at 30m' question.

Now i know the answer is .04 bar but.......

No. That's the answer to the exam question.
Never confuse this with reality.

we got onto the subject of O2PP and exhailed gas and knowing that we breath out 16% O2.

At 20m the PP of air in is aprox .6bar O2 and 2.4 bar Nitrogen.

so would air breathed out be

.56 bar O2 , .04 bar co2 and 2.4 nitrogen?

cos i'm reconing that .16bar x 20m= .48 dosn't sound right.

LOL.
You consume about one gram of oxygen a minute, or less. That's about 1L, or less, on the surface. You exhale a similar amount of CO2. Higher pressure = smaller fractions. At 20m on a 20L/min RSV you are putting 60 surface Litres through yourself containing about 12.6L of O2 and you consume less than a litre. Exhaled O2 is over 19%.
The ppCO2 is more constant but it sets your RMV so although the 0.04 is ballpark don't believe it.

 

[Seadeuce]

Presuming that your body is using oxygen at the same rate, you'll be breathing out a much higher percentage of O2 than you would at the surface.

The percentage that you breathe remains constant.

At 20m it would be still 21% of the total, increased, volume.


Seadeuce

 

[Brick]

No, what I said was correct. The percentage of oxygen in inhaled air remains the same, as you said. The partial pressure of oxygen in the inhaled gas will increase in direct proportion to the ambient pressure. The percentage of oxygen in the exhaled gas, though, will climb as a smaller fraction of the total oxygen is being removed by the body.