THE EE WAS USING A HOSTSEY STEAM CLEANER TO WASH UNDER THE HOOD OF A SERVICE LUBE TRUCK. THE EE HAD COMPLETED WASHING UNDER THE HOOD AND WAS WORKING ON WASHING THE REMAINDER OF THE TRUCK WHEN THE EE WAS WALKING BACKWARDS AWAY FROM THE SERVIVICE TRUCK AND SLIPPED AND FELL ON A CHOCK BLOCK ON THE WASH BAY FLOOR. THE EE WAS DIAGNOSED WITH A CONTUSION TO THE LEFT RIB.