A prisoner who is unable to breeze could, very well, still be able to chill.
Also, Carfentanil is intended for use in large animals such as elephants, making it less human.
There is a very long list of ways to kill a human being so quickly that they would be unable to perceive it, or render them unconscious before killing them in whatever way you want, or, or, or…
The choice of method is a political question, not a technical one. Yes, it would be easier to gas someone with N2, or He, or whatever. Yes, showering in carfentanil would do it, as would a howitzer round to the skull or explosive decompression, and they’d never know what hit them.
The choice of method is based on hoary historical precedent, and the relative squeamishness/bloodthirstiness of the legislature, prison system, and judiciary at the time in question. We want executions to have witnesses, but not be open to the public. We want to render prisoners unconscious before stopping the heart, but not shoot them in their sleep. We will let a prisoner have a feeding tube forced down their throat but lethal drugs must be administered IV, etc. We will suffocate you with toxic gas but can’t let you suffocate from suppressing your respiratory drive with opioids. We’ll shoot you in the heart but not in the head.
There’s no point in looking for a consistent logical basis to all this.
Sometimes the SDMB disappoints me. The OP posed the question whether a condemned prisoner *can ask *to be put unconscious. Yes, they can ask.
They may ask in the same way they may also ask to just be let go.
Both will be entertained with the same considerations
None
I don’t understand why nitrogen is not used. It’s cheap, easy to use, leaks from the chamber are not harmful to witnesses (unless it’s a massive leak), and no need to search for a vein.
It seems to me an obvious method of execution.
Someone upthread mentioned how anxiolytics can be given to someone about to be executed, but it varies by state. It didn’t mention if the condemned can be asked to be knocked out with drugs, then have their unconscious body strapped into the electric chair or put in the gas chamber.
You appear not to have read the entire OP.
Besides that, that no one until now took the course of an excessively literal reading of the question is encouraging rather than disappointing.