EE WAS WORKING ON ELECTRICAL STARTER SLED IN SHOP FOR RECONDITIONING AND REPAIRS TO THE HIGH VOLTAGE DISCONNECTS INSIDE CABINET. A 4'LADDER WAS LEANED AGAINST CABINET IN THE FOLDED POSITION & EE WAS STANDING ON 1ST RUNG. THE LADDER COULD NOT BE PROPERLY OPENED SINCE SLED BASE WAS NOT WIDE ENOUGH. LADDER SLIPPED CAUSING EE'S LT. ARM TO COME IN CONTACT WITH BRACKET. CUT UPPER ARM.