After landing at the airport, the pilot asked ground personnel to fuel the helicopter, while he prepared a sling load for his next flight. The pilot said that while he was weighing the sling load cargo on a nearby scale, the ground crew finished fueling the helicopter. The pilot then signed the fuel delivery manifest for the 25.4 gallons of “avgas” aviation fuel. Shortly thereafter, the pilot boarded the helicopter and started the engine. He said that after liftoff he picked up the 775 pound sling load, and then departed towards his destination. About 10 to 15 seconds after takeoff the engine began to run rough and lose power, so he elected to land, but while attempting to set the sling load on the ground, all engine power was lost. The low rotor warning horn sounded, and the pilot entered a low altitude emergency autorotation and attempted to cushion the landing, but the helicopter landed hard. The helicopter sustained substantial damage to the fuselage, and tail rotor drive system. A postaccident inspection by a Federal Aviation Administration (FAA) inspector revealed that the reciprocating engine helicopter had been inadvertently serviced with Jet A turbine fuel. In a written statement given to the FAA inspector, the ground personnel who fueled the helicopter stated that they thought they were fueling the helicopter with avgas, but they were using the same trailer that they used to fuel larger (turbine powered) helicopters.