It came out that the state of Alabama is preparing to execute a prisoner by nitrogen hypoxia. Oklahoma and Mississippi are the only other states that have authorized this method of execution. The prisoner, Kenneth Eugene Smith, had previously selected nitrogen hypoxia as a secondary means of execution. This decision was backed by the US Supreme Court. The first attempt to execute Smith by lethal injection failed because of the inability of workers to find a vein after 4 hours trying.
Smith’s attorneys have made the argument that this new form of execution claim that Smith is a “test subject for this novel and experimental method.” According to the Death Penalty Information Center, some have claimed that “those who support the use of nitrogen hypoxia can only theorize that the method will be painless and quick, but opponents have likened it to human experimentation.”
Criticism of the nitrogen hypoxia method have raised safety concerns for witnesses. It’s been argued that nitrogen escaping from the condemned man’s mask could threaten the health of those nearby, particularly the preacher standing close for spiritual comfort.
Critics say that the state of Alabama has not adequately prepared for the execution and the safety of witnesses and workers nearby.
“They could start to hyperventilate because their body would detect that they’re in a low oxygen environment,” said Dr. Joel Zivot, an anesthesiologist and associate professor at Emory University School of Medicine. “And that severe hyperventilation can lead to a stroke.” The doctor expressed concern that the method is full of unknowns and seemed quite skeptical of the method.
Seems to me that on basic principles alone, this method should work just fine. It would’ve been nice to read that the state had a written procedure that specified the type of mask and the nitrogen flow rate. As for the safety of others, minimally there should be an O2 concentration meter present, which is the case. The air exchange rate in the room can be measured and increased, assuming this is possible in an Alabama prison. Best of all, supplied air hoods or masks are widely available. This would only require an air compressor in fresh air.
Lamentations on Chemistry 
This is a safety issue at power plants when a boiler is drained and given a “nitrogen cap” to replace ambient air to prevent or reduce corrosion. When the boiler is opened back up, nitrogen can hide out in pockets and create unsafe conditions for workers. I agree that it seems like a reasonable option to lethal injection. Plenty of ways to make it safe for all attendants.
Never considered the possibility of pockets of bad air.
Confined space entry is serious business. Here we have to file for a permit which, if granted, releases a chain of resources and tasks to be done prior to entry. There is always one person near the entrance who is already in supplied air and is ready for entry to rescue the first worker in.
That was the case where I worked too, but sampling is an imperfect science and the attendant was not always within eyesight. In some cases we had radios and the attendant would check in periodically.