I have never done CPR on a person that i did not break a rib. American Heart Association (AHA) Recommends that you press approx. 2"-3" deep on compressions which requires much force. It is a life over limb matter. The person is dead otherwise you would not be doing CPR. They would be happier I'm sure to live with broken ribs than to die because the depth of your compressions didn't provide adequate profusion to their tissues. AHA is actually starting to suggest even faster and deeper (current guidelines recommend 100 compressions per minute) so yes it is VERY normal to break ribs with correct CPR. I just performed it about 5 and a half hours ago and sure enough... I'm not saying that you should be barbaric and by no means should you use rib breakage as a guideline to the proficiency of your CPR but the fact is the ribs attach directly to the lateral sides of the sternum and WILL break in most cases.