I wonder if carbon dioxide would be just as effective as nitrogen. It would have the benefit of carbon sequestration, right?
The end result would be the same: death. But CO2 causes the suffocation panic effect ("I can't breathe!"), while N2 does not.
N2 is absolutely the best - and cheapest - way to go. A little buzz like from alcohol and then the big Nothing. I simply do not understand why any state would go with the lethal injection regimen. Complicated, distressing (oh, wait, perhaps of that), and expensive. A quarter's worth of N2 will do it, and much more humanely.
No. You have sensors in your physiology that cause you to breath when CO2 gets above a certain level. There is no similar mechanism for nitrogen gas. You simply cease getting oxygen when the "air" you are breathing is changed to pure nitrogen. A few seconds and you pass out. A couple minutes later the brain and heart fail for lack of oxygen.