On March 3, 2019, about 0013 mountain standard time, a Bell 407 helicopter, N450AM, was substantially damaged after landing near Union Center, South Dakota. The pilot and flight nurse were not injured. The flight paramedic sustained minor injuries. The helicopter sustained substantial damage. The helicopter was owned by Air Methods and operated under the provisions of Title 14 Code of Federal Regulations Part 135. Dark night visual meteorological conditions prevailed, and a company visual flight rules flight plan was filed and activated for the flight. The on-demand air medical flight departed Spearfish, South Dakota, about 2337, and was en route to Union Center to pick up a patient.The helicopter had arrived at the landing zone at Union Center to pick up a patient. After landing, the pilot rolled the engine throttle to idle and briefed the flight crew that they were clear to depart the helicopter. About 20 seconds into the "cool down" process the ground ambulance drove towards the helicopter and subsequently the main rotor blades impacted the top of the ambulance. The flight paramedic was thrown to the ground during the collision. The main rotor blades, tail boom, and fuselage sustained substantial damage. The ground ambulance driver saw the crew open the doors and get out of the helicopter, so he moved the ambulance forward to get closer to the helicopter. The ground ambulance driver stated that he did not realize "that the helicopter blades were still rotating." Air Methods confirmed that the ambulance driver had received their training. A review of that training indicated that ground personnel are not to approach the aircraft until the blades had stopped rotation. The training also indicated that ground vehicle lights should be turned off while the helicopter is landing. An excerpt from the Air Methods General Operations Manual stated that ground personnel will not come beneath the rotor disk until directed to do so by the pilot in command; the pilot will use appropriate hand signals to do so.