They are not gas chambers, they are vacuum chambers that suck the air out and the animals die of lack of air. They should get their terms correct and they should suggest BETTER alternatives if they are going to take away one method. It is impossible, unfortunately, to keep every stray animal that is brought in to shelters alive for the length of their natural lives.
There is nothing wrong with using a “vacume chamber”.
it is painless and the affects are actually pleasant.
Yes, I have been in one. Every millitary aircrewman has. your troop inside, plug in your airmask and the drop the pressure to equal 30,000+ feet. Then you remove your mask and breath the thin air... first you loose fine motor coordination, then you get a little giddy, then your vision starts to blurr and you put your mask back on (or the attendant does it for you).
The air feels fine as you breath it, there is just not enough 02 in it to support life.
coming back down (repressurizing) can be painfull if you don’t clear your ears as you go.