(a) A person, peace officer, officer of a humane society, or officer of an animal shelter or animal regulation department of a public agency shall not kill an animal by using either of the following methods:

1. (1) Carbon monoxide gas.
2. (2) Intracardiac injection of a euthanasia agent on a conscious animal, unless the animal is heavily sedated or anesthetized in a humane manner, or comatose, or unless, in light of all the relevant circumstances, the procedure is justifiable.

(b) With respect to the killing of a dog or cat, a person, peace officer, officer of a humane society, or officer of an animal shelter or animal regulation department of a public agency shall not use any of the methods specified in subdivision (a) or any of the following methods:

1. (1) High-altitude decompression chamber.
2. (2) Nitrogen gas.
3. (3) Carbon dioxide gas.