THE RT FRONT SEAT PASS'G EXITED THE ACFT VIA THE RT DOOR AND WENT FORWARD OVER THE LEADING EDGE OF THE WING WHILE THE ACFT ENGINE WAS IDLING AT APRX 1200 RPM. THE ROTATION PROP STRUCK AND INJURIED THE PASS'G WITH SERIOUS CHEST, BACK AND ARM LACERATIONS. THE PLT STATED THAT HE HAD STOPPED THE ACFT IN TRANSIENT PARKING AREA ANS WAS LOOKING FOR HIS CHECKLIST WHEN THE RT FRONT SEAT PASS'G ASKED HIM IF HE COULD OPEN THE RT DOOR SLIGHTLY TO GET SOME AIR. THE PLT SAID THAT HE APPROVED THE OPENING OF THE DOOR. ACCORDING TO THE PLTS STATEMENT THE PASS'G 'HOPPED UP AND EXITED THE ACFT' A FEW MOMENTS LATER, SAYING THAT HE WOULD BE RIGHT BACK. THE PASSG SHUT THE DOOR AFTER LEAVING AND JUMPED FOWARD INTO THE PROP. THE PLT GESTERED IN AN ATTEMPT TO WARN HIM BUT WAS UNABLE TO BE EFFECTIVE DUE TO NOISE & THE CLOSED DOOR. THE INJURED PASS'G IS EXPECTED TO RECOVER WITH NO PERMANENT DISABILITY. IN ADDITION TO LACERATIONS HE SUFFERED A PUNCTURED DIAPHRAM AND A COLLAPSED LEFT LUNG. HE SAID HE FELT PARTIALLY AT FAULT BUT ALSO FELT THAT THE PROP SHOULE HAVE BEEN STOPPED.