EE WAS REMOVING DIFFERENTIAL FROM END DUMP USING FLOOR JACK. AS HE WAS POSITIONING HIMSELF & THE LOAD, THE JACK MOVED CAUSING HIM TO LOSE HIS BALANCE. AS HE FELL, HE REACHED OUT TO CATCH HIMSE LF. HIS HAND GRABBED THE JACK FRAME WHERE THE HANDLE GOES UP & DOWN. HIS WEIGHT CAUSED THE HANDLE TO GO DOWNWARD CUTTING HIS LEFT THUMB SEVERELY BETWEEN THE NAIL & THE FIRST JOINT.