EMPLOYEE AND A CO-WORKER WERE TO INSTALL & SECURE AN AIR BLASTER ON THE TERTIARY DUCT. THE TWO EMPLOYEES SUSPENDED THE BLASTER 6' ABOVE THE CAT WALK WITH A 3/4 TON CHAIN FALL AND ATTACHED THE SAFETY CABLE. A FOUD INCLE PIPE FLANGE CONNECTION WAS MISALIGNED, EE PUSHED BLASTER BACK TO GET BOLT HOLE ALIGNED. THE BLASTER SLIPPED COMING FORWARD THUSH HITTING EE'S THUMB BETWEEN THE TW