Don’t stick your head down in it then inhale!
I noticed this morning the tape holding temp probe onto the side of the carboy was coming off. So I reached down to slap a new piece of tape on and nearly passed out from the fumes! Burned all the way into my chest!
Duh! CO2 is heavier than air so the thing was filled with CO2 and whatever other crap the yeasties were belching up.
Yup, been there, done that.
You just acid-washed your alveoli.
Yeah it hurts and you get super light headed. I sometimes forget about it and take a breath and very quickly remember…
;D ROFL!
Just open the drain hole. 
LOL…I must have some clean alveoli.
Done that one too many times drying up water condensation inside because I didnt have any damp-rid.
Thanks for reminding that I need to check the damp-rid in my freezer. I’m most likely due to change it out.
Paul
Glad I could help haha.
+1 (a few times! Now the damp-rid is a permanent fixture in the freeze)
Another +1. After doing that a few too many times I finally ordered some damp-rid, which just arrived this morning. Woo-hooo no more acid-washed alveoli!!
So damp-rid absorbs the gasses coming out of the fermenter?
No it absorbs the condensation that forms on the side walls and on the floor from a chest freezer at below freezing temps…hence eliminating the need to stick my head down there to wipe up the little puddles and acid wash my alveoli lol.
I love sticking my head in there for a little whiff. It burns so good.
First time scared the poop out of me, though.
LOL. I have not done that before but the smell in the chest freezer when I am fermenting in there is something else. I can only imagine what it would be like to take a big whiff. 
Typo
Thanks Tom!
How long before damp-rid typically needs to be changed out if you have your controller set to about 64F? (Not that a couple degrees is going to make any difference…)
It is more about the humidity where you live - the damprid dries out the air, preventing condensation. The more you are in and out of the freezer, the more often you’re going to have to change it out. I got the ones that have a little strainer that sits in a container, so as it absorbs water and dissolves it drips to the bottom. When it is gone, you dump the water, refill with more damprid, and stick it back in the freezer. Mine can easily go a couple of months without being replaced, but I don’t get into the freezer that often, I’m just swapping out kegs. When I ferment in the one freezer I have to replace the damprid more often, because that raised the humidity in there.
The first time was the last time I did that. It was a wake up call for sure. Now I just gentlysniff the air above the the fermenter in the freezer. You brew and you learn. 