On April 30, 1999, at 0730 central daylight time, a Bell 206B helicopter, N35WH, landed at the Brazoria 440L offshore platform, in the Gulf of Mexico. A platform worker was seriously injured when he walked into the helicopter's turning tail rotor blades. The helicopter was registered to and operated by Horizon Helicopters, Inc., of Houston, Texas. The airline transport pilot and his two passengers were not injured. Visual meteorological conditions prevailed for the Title 14 Code of Federal Regulations Part 135 non-scheduled, on-demand air taxi flight, and a company VFR flight plan was filed. The flight originated from the operator's private heliport, located near Matagorda, Texas, at 0715. The pilot reported in the enclosed Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that before takeoff he briefed the passengers on the safety procedures in and around the helicopter, as well as over water operations. During the approach to Brazoria 440L, the pilot noticed a crane operating on the platform. He circled the platform until the crane operator indicated that he had visual contact with the helicopter and ceased crane operations. The pilot stated that he maneuvered the helicopter so it approached the platform into the wind and clear of the crane, which upon landing, placed the tail rotor over the stairwell. After the helicopter landed and while it was still "light on the skids," he began to reposition the helicopter so the tail rotor blades would not be over the stairwell. Simultaneously, the rear passenger began to exit the helicopter without receiving authorization by the pilot. The pilot immediately aborted the repositioning maneuver and "lowered the collective full down, disarmed the floats, and rolled the throttle back to idle." Consequently, the tail rotor remained extended over the stairwell. The pilot reported that a few seconds had elapsed when he felt a "nick in the pedals." Subsequently, one of the passengers notified the pilot that a platform worker had walked into the turning tail rotor blades. The platform worker received a 3-inch laceration to his head and suffered a fractured skull. During telephone interviews conducted by the NTSB investigator-in-charge, both passengers stated that the helicopter was parked and that the pilot never indicated to them that he was going to reposition the helicopter. According to the passengers, they heard the engine power "spool down" and exited the helicopter. The front seat passenger stated that he had gone to the rear cargo door to help the other passenger unload the helicopter when he saw the platform worker coming up the steps. He added that before he could do or say anything the worker walked into the turning tail rotor blades, which were positioned directly over the stairwell. The pilot reported that the following weather conditions existed at the time of the accident: clear skies, visibility greater than 10 miles, temperature 73 degrees Fahrenheit, and wind from the east at 30-35 knots. The helicopter was inspected by the pilot immediately following the incident and no damage was noted. Subsequently, the tail rotor was inspected by an FAA certified airframe and powerplant mechanic. The mechanic stated that no visible damage was observed to any part of the helicopter.