I was browsing on YouTube and found this video that demonstrates how fast and how severe a PTO entanglement can be. Loose clothing and long hair that isn’t tied back can easily become tangled. I forget who it was, but I remember talking to someone who got his sleeve caught in a PTO shaft and luckily his sleeve tore off and he wasn’t pulled in.
Ideally, the best way to prevent entanglement is to make sure the PTO is off if there is anyone on the ground near it. While that might not be practical 100% of the time, the more you can think of ways to avoid having someone standing next to a running PTO shaft, the more you can reduce the risk. Stepping or reaching over a running PTO shaft is especially dangerous, and there is a strong temptation to just step or reach over if you need something on the other side rather than walking around, but it’s one of those situations where taking the extra minute to go around significantly reduces risk.
Guards are also prevent PTO entanglement, especially ones that cover the joints as well as the PTO shaft. I’ve seen multiple cover designs that have ends that are retractable or have holes cut in the guard to allow for greasing. Overall, the retractable ones seem to work better but I think it depends on the particular piece of equipment too. Check out AgriSupply for a variety of PTO guards that seem to be priced a little lower than some of the other suppliers.