Quote Originally Posted by Dave763 View Post
Recommendations—Carbon dioxide is acceptable for euthanasia in appropriate species (Appendices 1 and 2). Compressed CO2 gas in cylinders is the only recommended source of carbon dioxide because the inflow to the chamber can be regulated precisely. Carbon dioxide generated by other methods such as from dry ice, fire extinguishers, or chemical means (eg, antacids) is unacceptable. With an animal in the chamber, an optimal flow rate should displace at least 20% of the chamber volume per minute. Loss of consciousness may be induced more rapidly by exposing animals to a CO2 concentration of 70% or more by pre-filling the chamber for species in which this has not been shown to cause distress. Gas flow should be maintained for at least 1 minute after apparent clinical death. It is important to verify that an animal is dead before removing it from the chamber.
Excellent post Dave. This just goes to prove why compressed CO2 gas in cylinders is humane - it can be precisely regulated.

And it shows why using dry ice is extremely inhumane to the mice - there is no way whatsoever that the flow rate of the CO2 can be precisely regulated and the mice can suffer a horrible and agonizing death.