AT APPROX. 4:15PM EE WAS RESETTING SHIMS JAW CRUSHER. EE HAD LOOSENED TENSION SPRING WITH IMPACT WRENCH JACKEDSAW OPEN NEEDED TO LOOSEN SPRING SOME MORE, PUT IMPACT BACK ON NUT, WHEN PULLED TR IGGER ON, IMPACT NUT CAME OFF RELEASING SPRING CAUSING HAND TO BE PINCHED BETWEEN AIR WRENCH & MOTOR FRAME, MASHING THUMB.