The way a vaccum works is basically no different than a CO2 Chamber. Both system basically remove oxygen and suffocate the animal. When done correctly, a co2 chamber is actually MUCH more humane than a vaccum. All a vaccum does is remove all oxygen, essentially suffocating the animal. A co2 chamber, however (when administered correctly only), will result in a far more painless death. When initially administered at a 30-40% concentration, CO2 is a general anasthetic. After the animal is sedated, the concentration can be increased in order to suffocate the animal.