What was found
A/C SHUTDOWN IAW THE SHUTDOWN PROCEDURES CHECK LIST. AFTER THE ENGINE WAS TURNED OFF AND THE MAIN ROTOR RPM WAS AT APPROXIMATELY 120, THE FLT MEDIC OPENED THE RIGHT SIDE CABIN DOOR AND STEPPED OUT OF THE AIRCRAFT. THE WINDS AT THE AIRPORT WERE APPROXIMATELY 260 DEGREES AT 15 KNOTS. THE A/C WAS PARKED ON A DOLLY THAT WAS ORIENTED APPROXIMATELY 90 DEGREES TO THE WIND - ON A HEADING OF APPROXIMATELY 170 DEGREES. THE WINDS BLEW ON THE CABIN DOOR TO THE POINT THAT THE AIR PISTON THAT HOLDS THE DOOR AT ABOUT 90 DEGREES IN THE NORMAL OPEN POSITION BROKE LOOSE FROM THE AIRCRAFT MOUNTED POINT AND THE DOOR OPENED TO A 180 DEGREE POSITION WITH THE TOP OF THE DOOR BEING ABOVE THE CABIN LEVEL IN THIS POSITION. DURING THIS EVENT, THE ROTOR BLADES WERE SLOWING DOWN - THUS DROOPING TO A LOWER POINT IN THE ROTATION PATH. THE ROTORS STRUCK THE TOP OF THE DOOR BREAKING THE DOOR WINDOW AND DAMAGING THE TOP EDGE OF THE DOOR. ALL THE ROTOR BLADES WERE DAMAGED AS WELL DUE TO THE DOOR STRIKE. THE RIGHT CABIN DOOR AIR PISTON FAILED TO SECURE DOOR RESULTING IN THE DOOR OPENING 180 DEGREES AND THE TOP EDGE CONTACTING THE MAIN ROTOR BLADES. AIRCRAFT GROUNDED FROM FLIGHT DUE TO DAMAGED MAIN ROTOR BLADES AND RIGHT SIDE CABIN DOOR NON-SERVICEABLE