Leaving the chuck key in the chuck on a lathe or drill press is dangerous. Where I work we confiscated all of the conventional keys and replaced them with spring loaded keys that can't be left in the chuck. They were attached to the machine with a cable. We wrote up several production people that didn't get the repeated messages and used the ones they had hidden in their tool box.
I worked in a machine shop for a short period of time. I once left a chuck in a Warner Swasey #5. I was inexperienced, young, stupid and lucky, because I had also left the machine in reverse.
Sent the chuck through the side of the steel pole building, leaving a gaping hole in it.
I went outside and dug it out of the snow bank.
Had I been smarter, it would have been my left shoulder - but you can't count on stupidity to always bail you out. A sheet of steel and a fistful of pop rivets fixed the building - I wouldn't have been that lucky if I hadn't been that unaware.
I'm still haunted by that one.
One of the most beautiful girls in my high school caught her hair in a small engine lathe in shop class. Had it been a dozen hairs more, it would have drug her face right into the chuck. As it happened, she wound up with a bad haircut for the rest of the semester.
One of my best friends in high school broke his leg in gym class. He shared a hospital room with a farmer who got his new Key bib overalls caught in an unguarded power takeoff on a tractor. There wasn't an extremity on that man that didn't have something broken.
I worked for a short period of time at a rubber molding company in Waukesha. Part of the process was feeding rubber into a heated roller. A co-worker got his hand stuck, and despite the deadman switch, the roller had to be removed to extricate his hand from the machine.
When I saw this post, and then clicked on the link and saw a lathe operator, my stomach turned. I stopped the video and rechecked the initial posting - "no blood or gore". Had I not re-read that, I would have skipped the rest of the video entirely.
I've seen enough of it, but it's good to be reminded that I've seen enough of it.