EMPLOYEE WAS WALKING TOWARDS THE LADDER THAT LEADS UP TO THE SECOND LEVEL, WHEN HE STEPPED ON THE SUMP CYLINDER. HIS FOOT SLIPPED BECAUSE OF THE WET WEATHER CONDITIONS & WHEN HE SLIPPED HE FELL ONTO THE UNCOVERED DODGE COUPLING ON THE #2 HORIZONTAL MOTOR. HE CUT HIS RIGHT THUMB. THE CUT WAS APPROX. 1"" LONG.