CREW WAS LOOSENING THE MANTEL ON A CONE CRUSHER.THEY HAD A CHAIN 3/8 GR. 80 TIED TO THE MANTEL &HOOKED TO A LOADER PULLING ON IT. A PORTA-POWER WAS BEING USED IN CONJUNCTION WITH THE CHAIN. TH E PORTA-POWER FAILED BINDING THE MANTEL UP WHICH CAUSED AN OVERLOAD ON THE CHAIN, THE CHAIN BROKE, WHIPPING EE ON THE LEFT SHIN/CALF AREA.