Animal gas chambers are cruel and inhumane but still legal in many states as a method of killing shelter animals. Studies indicate that killing shelter animals using carbon monoxide can result in prolonged suffering and distress, particularly among old, pregnant, sick or injured animals unable to readily absorb the gas.
The gas chambers also put shelter workers at grave risk of carbon monoxide poisoning. In North Carolina, for example, there are documented incidents of gas chambers leaking CO gas and injuring workers, and in Tennessee gas chambers were banned after a worker died from exposure to CO gas while removing animals from the gas chamber.
The National Animal Control Association and Association of Shelter Veterinarians have condemned use of animal gas chambers. In recent years a number of states have banned them. The resolution calls on all states to stop using animal gas chambers and implement humane euthanasia by lethal injection. For more on the resolution: http://www.animallawcoalition.com/gas-chambers/article/2050