I read that only a twelve inch fall can create enough force to break ribs using a single strap safety harness.
There really are some huge forces there that are oftenunderestimated.
I use fall-protection fairly often at work. One of the things included in our training is that a 200 pound human falling a short ways of15 feet or so can exert almost 5,000 pounds of force on the anchor point to which he is tied.
Not something I want to experience.