I saw a video by a fireman the other day. He used an O2 meter to show that the levels of O2 were dangerous and out of line with OSHA requirements. Wish I saved it.
A little bit of common sense would show many of those tests to be flawed.
Is there a buildup in the mask? yes.
Does the mask prevent co2 from leaving or from o2 entering? no.
How much air does one breath contain? on average about 1/2 liter.
How much volume can a mask trap? Try it. Probably 50ml?
Where does the rest of the inhaled or exhaled breath go? around and through the mask.
As for the testing - what is the tidal volume of the sensor? probably a lot - meaning that when it senses something, it takes a while for the sensor volume to be refreshed for a "fresh" reading.
Wearing a mask is definitely a problem, but nobody is breathing 5-6% co2 in any breath, and 450ml of 20% o2 is still a livable amount.
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