Idk that I agree with Nitrogen leaks being a big concern - I don’t know enough for certain to say one way or another really - but supposing they are a risk, regardless I think the biggest risk to the executioners or viewers is the psychological one.

Even convulsions after death that truly aren’t experienced by the convict can still greatly disturb the people who see them. Plus, in general, the psychological toll of systematically killing people who can’t fight back as one’s ‘mundane’ job. It’s gotta fuck people up. Maybe along the lines of how drone pilots - who effectively go to war, but who aren’t surrounded by fellow soldiers all the time like regular soldiers, but instead who go home every to friends and family who aren’t at war, causing prolonged feelings of alienation and separation that tend to hit regular soldiers only after they come home from deployment - end up with a lot of ptsd problems.