EMPLOYEE WAS WORKING ON SHOT, THE FOREMAN OF THE QUARRY CAME BY & INFORMED THE CREW THAT HE WAS CANCELLING THE SHOT DUE TO WEATHER CONDITIONS. THE TRUCKS WERE PARKED IN AN AREA WHICH WAS MUDDY & SLIPPERY. AS THE EE GOT INTO THE PASSENGER SIDE OF UNIT 1178 HIS FOOT SLIPPED & HE FELL FORWARD HITTING HIS CHEST AGAINST THE TRUCK DOOR FRAME.