EE WAS WORKING ON NEW TYPE POSITIONING VALVE ON #44 SILO. THE VALVE HAD TO REMAIN ENERGIZED DUE TO THE WORK THAT WAS BEING DONE. EE BEGAN THE CYLINDER TO THE VALVE HE FORGOT TO SHUT OFF THE AIR THAT POWERED IT. WHEN HE STUCK HIS FINGERTIPTHROUGH THE CLEVIS TO ALIGN EVERYTHING THE CYLINDER RETRACTED CUTTING OFF FINGERTIP. NO BONE INVOLVED.