Cheap. Abundant. Renewable. Fertilizer. Effective. Kills bad people.
The only downside is that it’s painless.
Nitrogen hypoxia is a common method of euthanizing stray animals. It is about as painless as possible.
The discomfort often associated with suffocation is caused by carbon dioxide. When one suffocates because of lack of circulation, the victim breathes in his own carbon dioxide. Elevated levels of CO2 in the blood stream trigger a painful and agonizing reaction. With nitrogen hypoxia, the victim passes out from lack of oxygen long before any distress is sensed.
In addition, there are no toxic chemicals or drugs which might injure prison personnel and require stringent security. It’s win-win.