The pilot reported that he had started the right engine and was about to select the generator ON when he inadvertently touched the left engine start switch momentarily. The pilot was aware that the left door was open and loaders were completing last-minute loading. Shortly afterwards, the pilot was advised by the senior base pilot who was in attendance that the left propeller had rotated briefly and struck a loader who was walking towards the front of the aircraft. The loader was uninjured and the flight proceeded as planned. As the result of an inquiry by the freight company, the following recommendations were made and have been accepted by the aircraft operator: 1. Development of a documented training program on tarmac operations and procedures. 2. Implementation of a recurrent training program for tarmac personnel. 3. Loading personnel to be certified or "signed up" for single-engine turn-around and loading procedures with engines running. The operator has included training on "error types" and prevention strategies as part of the company's in-house human factors management on initial and recurrent training courses. During the regular monthly safety meetings pilots have been alerted to the need for propeller and personnel awareness.