WHILE REMOVING A 156 POUND CLAMP, THE EE WAS HOLDING ONTO THE BOTTOM HALF WITH BOTH HANDS. THEN THE EE REMOVED ONE HAND TO GIVE THE HOIST SIGNAL TO THE CRANE OPERATOR. AS THE CRANE BEGAN TO HOIST, THE BOTTOM SECTION OF THE CLAMP FELL, JERKING HIS LEFT ARM. BECAME AWARE OF MEDICAL TREATMENT 5/17/05.