The air medical helicopter had responded to a call for service, and after landing was sitting idle with the engine running and its rotors turning while the flight medical crew and two local volunteer fire department personnel transferred a patient from a stretcher into the helicopter. Once the patient was loaded, a flight medical crew member told the fire department volunteers they could leave the rotor disk area while they finished securing the patient inside the helicopter. A flight medical crew member then observed one of the volunteers move the stretcher back and away from the helicopter; however, the two volunteers did not leave the rotor disc area. A few moments later, a flight medical crew member watched the unattended and unsecured stretcher roll downhill toward the helicopter’s spinning tail rotor. The stretcher collided with the tail boom and the tail rotor resulting in substantial damage to both tail rotor blades and minor damage to the tail boom.