TWO EMPLOYEES HAD THE LID OF THE IMPACTOR IN THE RAISED POSITION TO CHECK OUT A PROBLEM. THE WEDGE SHAPED STOP BLOCK WAS IN ON ONE SIDE. VICTIM WAS ADJUSTING THE BLOCK ON HIS SIDE. HIS LEFT TH UMB WAS PINCHED BETWEEN THE TOP OF THE BLOCK AND THE BOTTOM OF THE HOOD. HE LOST THE THUMBNAIL.