Ever since I was a kid I always wondered how people are not suffocating from staying in their house. Like if all windows are closed how does air get in? Wouldn’t we just breath up all the available air in a matter of hours and die? Same goes for cars too. If I’m on a long road trip and the windows are closed how am I still alive?
In: 2
a. Very few things are completely air tight. And at all exchange areas there will be diffusion, where just random air molecule bouncing around means that any differences in air mixture will try to even itself out (if there is higher/lower Oxygen/CO2 etc it will balance itself).
b. Generally the there is sufficient air volume (more volume means that it takes longer time to create a noticable different) and enough places where diffusion is happening that you won’t notice it.
However, in for example a classroom (especially in schools without a very high ceiling, ie less air volume) there is frequently enough people in a place with bad enough ventilation that the increase in CO2 will have an effect by the end of the day. The feeling of air being “stuffy” is directly related to the body detecting a higher amount of CO2 in the air because funnily enough the body is unable to detect different levels of oxygen (we have no nerve cells that measure oxygen levels), but it’s extremely sensitive to levels of CO2. As we breathe we exchange Oxygen (O2) and Carbondioxide (CO2) on a 1 for 1 basis, but since the atmosphere contains 21% oxygen but only 0.04% CO2… well, 0.4% of Oxygen is a really tiny relative change in oxygen levels but it’s a massiv relative change in the amount of CO2 (increasing it 10 fold).
P.S: Note that a human will process about 11 cubic meters of air per day. If we’re breathing atmospheric air that’s 21% oxygen and 0.04% carbondioxide in and 17% air and 4% carbon dioxide out. The air we breathe out will almost instantly mix with the air in the room and create a new equilibrium (while diffusion with the atmosphere will try to balance that back towards the atmospheric balancing point). We’re physically pretty sensitive to oxygen changes, but we can handle down to 15-18% oxygen until problems get really serious (depending on how you define serious). However, if CO2 levels in a room rise to even a percent you will feel seriously uncomfortable (headaches, nausea etc).
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