1972 Ascot, Acording to the poster, Hi injuries were limited to a broken pelvis and on the initial flip his hand hit the quck release. AMAZING!
This was a California Racing Assoc. (CRA Sprint Cars!) race at the great Ascot Park, in Gardena, CA. June 10th 1972, heat race action, John Kellar flips over Frank Burgin's car. While he was upside down, Kellar's hand hit the release on his seat belt quick release, and well, releasing him! He suffered only a broken pelvis, pretty amazing when you see the crash.
http://www.youtube.com/watch?v=w8XGbzzpUA0