The execution in Alabama went VERY badly. One of the witnesses wrote about what he saw, equating it to torture. Here's something written about it.
https://apnews.com/article/nitrogen...mate-lawsuit-7043bff9563f99d083b189ff7d39253c
The Alabama execution isn't an example of a good executed (no pun intended) nitrogen asphyxiation. There are reasons to believe the execution was botched with inferior equipment and gas, either for malicious purposes or just utter incompetence.
Unfortunately we haven't all the facts and the few we know of is used to advocate against execution overall. Questions I would like to know is
1. Was the inmate clean shaven?
2. Was the gas at a high enough purity and not mixed with any other gas like co2.
3. What kind of mask did they use
4. What flow rate was used, did they utilize some sort of reservoir tank to relieve the pressure inside the mask.
5 was the system indeed a constant flow, which I have lead to believe.
Regardless of these very important factors, we know the inmate held his breath and didn't willingly succumb to his death. If the system is indeed a constant flow, the gas will be limited to what the current gas flow is. For example a flow rate of 40L/pm which is quite high will only provide you with 0,6 liter per seconds. So what happens when you hold your breath and finally can't hold it any longer?
You take a big breath, which is going to be much more than the 0,6 liter a second the setup is providing. Maximum lung capacity is like 6 liters so naturally the inmate will suffer mild case of suffocation. Being strapped and suffocated at the same time is quite traumatic, so witness saying he was fighting for his life wasn't an understatement.
Inert asphyxiation requires some form of cooperation with exit bag/constant flow setups. This wouldn't be the case with a on demand valves or something like an inclosed area. For a setup like the inmate experienced, you have to take small and constant breaths to not feel suffocated, if you try taking a deep breath you will struggle as the inmate evidently did.
Tdlr the nitrogen method isn't a good option for executions, unless you use on demand valves or something like the sacropod. Any method that requires cooperation is a recipe of disaster and the news will spin this story to discredit the usage of nitrogen.