Quiz - Physics - Partial Pressure of Carbon Monoxide

[inquis]

Yet in all exams the "correct" answer remains 7.5, which it is not.

Sorry, 7.5% is correct. Our physiology works on partial pressure (PP). At depth, you're clearly breathing a partial pressure of 7.5 atm. In order to have a PP of 7.5 atm on the surface, you need a fraction of 7.5% on the surface.

1.5% is 1.5% at any depth.

That's only true for a *fraction* of 1.5%. PP is dependent on fraction and ambient pressure/depth.

 

[Angelo Farina]

Sorry, 7.5% is correct. Our physiology works on partial pressure (PP). At depth, you're clearly breathing a partial pressure of 7.5 atm. In order to have a PP of 7.5 atm on the surface, you need a fraction of 7.5% on the surface.


That's only true for a *fraction* of 1.5%. PP is dependent on fraction and ambient pressure/depth.

For physics, I agree.
For physiology, I strongly disagree: the reaction of a living organism to a toxic substance in general is not linear.
The reaction is very weak for small concentration, then it becomes much more evident beyond some threshold, but after approaching an extreme reaction (death), the curve flattens agains.
It is called a sigmoid.
In the specific case discussed here, the mixture was already very toxic at surface, causing loss of consciousness and death in a couple of minutes.
Increasing the p.p. of CO by a factor 5 does not change significantly the effect: you probably loose consciousness and die in just 110s instead of 120s, but basically you are already at the top of the sigmoid curve, hence linear proportionality to the p.p. of CO is unrealistic.

 

[emoreira]

This question is in honor of @DandyDon - the CO king!

A scuba tank containing 1.5% carbon monoxide at the surface is taken down to 40 meters/132 feet. If a diver were to breathe from that tank at this depth, it would have the same effect as breathing ____ percent of carbon monoxide at the surface.

a. 1.5
b. 6.0
c. 7.5
d. 3.0



I will post a daily question from my exams to help newer divers and to encourage more experienced divers to interact gracefully and helpfully with the newer divers.

Reminder - this is a post in the Basic Forum and it is a green zone. Please be nice and on topic.

Thank you for your patience while we try to give people something to discuss other than Covid-19 and/or Politics. I will post the answer covered by the spoiler tag later today.

That tank will kill the diver at the surface almost immediatelly.