CAR WAS PARKED. I HAD OPENED DOOR MANUALLY. THOUGHT IT WASN'T FULLY OPENED; HIT POWER BUTTON ON DOOR JAMB TO OPEN FULLY. THEN LEANED AGAINST DOOR WITH LEFT HAND AND BENT OVER TO REMOVE ICE TRACKS FROM SHOES. DOOR CLOSED INSTEAD OF OPENING AND BEFORE I COULD REACT IT CLOSED AND LOCKED ON THUMB AND SEVERED IT COMPLETELY JUST IN FRONT OF KNUCKLE . SENSORS SUPPOSEDLY DESIGNED TO PREVENT DOOR CLOSING ON LIMBS DID NOT WORK. SENSORS ARE SUPPOSED TO PREVENT THIS INJURY, OR SO I THOUGHT. CAR HAS 3 BUTTONS TO ACTIVATE DOORS: OVERHEAD CONSOLE; REMOTE KEY & INSIDE DOOR JAMB. IF SENSOR DOES NOT WORK POWER DOOR COULD ACTIVATED FROM ANY ONE OF THESE LOCATIONS BY SOMEONE NOT FULLY AWARE OF ACTIVITY AROUND DOOR TO CAUSE SERIOUS INJURY.