That is certainly true for equilibrium conditions. But, when CO2 sublimes from a solid, it is much colder, and denser, than the surrounding air. Sure, given enough time, the concentrations will equalize, but if the layer of CO2 is considerably cooler than the surrounding air, the concentration of CO2 will be higher the closer you get to the bottom.
Here’s an aquarium two feet tall with a layer of CO2 in it. As excavating (for a mind) points out, concentrations will equalize if given enough time - but if you’re constantly replenishing the CO2 near the floor with a cooler that’s leaking pure CO2 gas, you definitely will have a CO2-rich layer near the floor; how rich and how thick of a layer will depend on the specifics of the situation.
I am not sure I understand your logic. If I read correctly, I think you are saying : I have a cube of dry ice in a room, the air in the room has sufficient thermal energy and heat transfer to the cube surface to sublimate CO2 at a high enough rate but the air then does not have enough thermal energy / heat transfer to bring the vaporized CO2 to the room temperature?
This again goes against everything I have experienced. The heat transfer rates from gases (air) to solids (cube of solid CO2) is much lesser than the direct mixing and heat transfer between air and CO2.
So the CO2 from natural sublimation of CO2 will not pool at the bottom. Unless you have forced sublimation by another heat source, which is not the case in the OP.
My wife is a safety instructor, and we have CO2 detectors in our house, by the time you feel any symptoms, you probably won’t make it to the front door.
Related question – I understand that carbon monoxide is especially dangerous because of the bonding to hemoglobin, and so there can be a cumulative effect of exposure to CO. (Please correct me if I’m wrong!) Is there a similar danger to persistent lower-level inhalation of CO2, or not?
I assume there isn’t because we are constantly expelling CO2, but just thought I’d ask.
CO2 detectors in homes are exceedingly uncommon, and probably of little value.
Are you perhaps talking about CO detectors (which every home that uses propane or natural gas should have)?
See hypercapnia: breathing an atmosphere of a few percent CO2 can cause acute symptoms, and breathing more than about 8% CO2 can kill you. This, in spite of there being enough oxygen in the air to sustain life.
CO2 gas doesn’t have to be cold to pool near the floor. Because of its molecular weight, it’s more dense than air even when it’s at the same temperature and pressure. In a quiescent, isothermal mass, mixing can only take place by diffusion; depending on the rate at which the dry-ice source is sublimating, it can take a while for the vertical CO2 gas concentration gradient to dissipate.
A definition first - Threshold Limit Value–Time-Weighted Average (TLV–TWA) The TWA concentration for a conventional 8-hour workday and a 40-hour workweek, to which it is believed that nearly all workers may be repeatedly exposed, day after day, for a working lifetime without adverse effect.
With the above definition - “Based on the long-term exposure studies, even though the majority of references are concerned with studies on physically fit males in confined spaces, a TLV-TWA of 5,000 ppm, is recommended. This value provides a good margin of safety from asphyxiation and from undue metabolic stress provided normal amounts of oxygen are present in the inhaled air.” taken from OSHA recommendations available here : https://www.fsis.usda.gov/wps/wcm/connect/bf97edac-77be-4442-aea4-9d2615f376e0/Carbon-Dioxide.pdf?MOD=AJPERES
Low oxygen could occur in coal mines, but a far more common danger was carbon monoxide, to which canaries are also sensitive.
Mice were tried, but they just curl up and go to sleep and you might not notice. A canary falls off its perch, which is more noticeable.
it doesn’t even take a separate source of CO[sub]2[/sub]. In the Navy, if a normally sealed watertight void is opened, it will be ventilated for a while before anyone enters. This is because if it was freshly painted before it was closed up last time, the paint oxidizing may have consumed enough of the O[sub]2[/sub] to be dangerous.
I’m just saying, before you put your limited theory into practice, you might want to look at that aquarium video, and possibly read up on how many people have died due to CO2 pooling in low spots.
I’m sure lots of us can work through the processes that allow pools of gaseous CO2 to exist, but for the OPs and other’s sakes, let’s not argue whether it does happen.
I build a lot of fermentation rooms and generally I model CO2 risk within 3’ of the finished floor while over time the room would even out the source is typically low and once you’re 5’ or so from the source the room will see stratification. As given above for daily work 8 hours per day 0.5% CO2 is the limit. If we say that your car is 100 ft3 and assume since you’re running the AC it’s 70 you have about 1000 mols of air in your car. CO2 is about 44 g per mol and once you get to 5 mols you’re above the daily limit threshold (not quite but it make for some easy math). So basically a 1/2 pound of dry ice is enough to make it so you shouldn’t sit in your car all day. With 2 to three pounds melting hopefully you leave your doors open long enough to completely change out the air 4-6 times per day.