From what I've heard, those who died at industrial sites using N2 instead of tool air simply worked till they got dizzy then keeled over to sleep. Of course they then suffocated but didn't know anything of it. Inside of those confined space vessels it no doubt took a while to displace the O2. That being the case then perhaps if administered slowly it would take longer but be more gentle or humane.
BTW OSHA now requires open vents where possible (confined space work) and/or forced fresh air. I have been in some vessels where a vacuum was used I suppose to keep from stirring up dust and rust. Same principal, it pulled air in from the outside through open vents. Hose was about 6"-8" and had a strong force, One night one of the contractors working inside needed to pee. Instead of making the 100' climb to get out at the top he decided to pee into the large vacuum hose. It grabbed him and people outside could hear him screaming. The machine was shut down with no lasting injury to the worker. He didn't do that again.
BTW OSHA now requires open vents where possible (confined space work) and/or forced fresh air. I have been in some vessels where a vacuum was used I suppose to keep from stirring up dust and rust. Same principal, it pulled air in from the outside through open vents. Hose was about 6"-8" and had a strong force, One night one of the contractors working inside needed to pee. Instead of making the 100' climb to get out at the top he decided to pee into the large vacuum hose. It grabbed him and people outside could hear him screaming. The machine was shut down with no lasting injury to the worker. He didn't do that again.

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