We had a hanger fall last summer, I cut a branch and it got stuck part way down, hidden in the other foliage, I called down to tell Bob to be careful we have a hanger, but we both forgot about it, when I was pulling up my refueled saw it let go, I heard it hit his helmet (he wears a rockman with a chinstrap) then it grazed his arm, scrapped up his upper arm pretty good. He still has a scar, thank God, only a scar. Shit, I was scared for a moment till he started cussing me out.
That was our worst incident, several things we could have done better, but no helmet, probably no Bob.