An employee was performing preventive maintenance activities that included cleaning coils on a turbine oil cooler. The employee used a 6-foot step ladder to access the mid-flange area, where he stood to access the oil cooler, apply silicon in-between the flanges, and bolt up the flanges. As he was standing on the side of the cooler, he fell from a height of less than 4 feet but managed to catch himself during the fall. In doing so, his left triceps contacted the threads of an existing stud that secured the top cover, resulting in a puncture wound that required hospitalization.