Gorillas are actually quite docile, relatively. They warn you, breast beating and bearing teeth, before they get violent. The worst damage I ever heard about from a gorilla was when a keeper got bit on the shoulder after he sprayed a silverback in the face with a high-powered hose. He forgot to lock the ape out while he cleaned his cage. He turned around and the ape was just sitting in the corner watching him. Keeper flipped out.
You think a chimp would have held that boy who fell in it's area, like that female gorilla did in Chicago, protecting him from the other gorillas? Not a chance. Chimps are nasty.
Yeah, I used to volunteer as a docent at a zoo. Happy times. Really good stories behind the scenes there.