Nitrogen Hypoxia will render you unconscious in under a minute when its almost pure n2 and exhaust is accounted for to remove co2. The last execution was done on such a sloppily manner you seriously have to question if the procedure was done in such a way that to ensure maximum suffering. The mask used didn’t allow co2 to be vented away, their method of execution was only one step up from wrapping a bag around his head.

A proper way to do it, probably not done because cost and some stupid unnecessary procedure, would be to construct a booth around a chair with exhaust fans near the base and a supply of pure n2 coming from the top. If the o2 and co2 can be removed quickly enough the body can’t tell its not getting enough to breath and loss of consciousness can happen quickly with death following in minutes. Smarter Every Day has a video on Hypoxia where Dusten, the content creator, is an altitude simulator where they are lowering the air pressure to simulate high altitude and by extension just a few short steps from a death chamber. The host goes through several stages of hypoxia and had to be told point blank to put his oxygen mask back on several times before he risks passing out. At no point does he show signs of pain or distress and if anything acting almost like hes high.

Building a chamber like this for executions would have been far more humane but they didn’t want to put more thought or money into it than strangling a guy so instead you get that botch job Alabama used.