chunkyfrog wrote:Exhaled air does NOT go down the tube;
it is VENTED out through the mask.
Unfortunately not quite true. When the mask is under pressure, a fixed flow rate comes out of the vent. During part of the exhale cycle, you may exhale more air than that. The excess air flow goes back up the tube. On cold nights, with my ComfortGel mask I used to use, I could see condensation in the elbow.
However, your exhaled air is "swimming upstream" against the air current, and probably doesn't make it far up the hose.
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As to dangerous germs in the humidifier water
Cleanliness is a good thing.
Stop and think about this for a while. If you're exhaling germs, you're already infected. If you're exhaling bacteria strain B23, you've already got it in your body. Every time you inhale, you're sucking B23 back into your lungs, even without CPAP. Even if you do get B23 into your water tank, it's not like you're not already breathing it.
Ebola or any other germ isn't going to appear in your CPAP equipment unless you already have it, or it's in the air in your house, or someone with Ebola handles your equipment.
Now, if you're sharing a CPAP machine, hose, mask, or water tank with someone else, that IS a problem. Duhhh..... You really should thoroughly clean and disinfect a used CPAP mask, hose, and water tank if someone else has used them.
It could be a problem if the germs multiplied greatly in the water tank and you're suddenly getting large doses of the bacteria you've already got. However, as long as you're using distilled water, germs can't grow very well in the water. Germs need some sort of food, and if it's just water and air in the tank, there's nothing to feed on to allow the germs to make more germs. The plastic used shouldn't be something that germs can feed on.
Even if germs are in your CPAP water, in theory, the germs will mostly stay behind in the water. Unless the humidifier creates droplets, it's only gasses that leave the tank. As the water evaporates, germs will be left behind.
Your mask itself is a little different because it's got sweat, oil, mucous, and other human goo on it. Still probably not really that good a place for germs to grow.