Something that has really bothered me in The Walking Dead was the part in the first season when Merle Dixon, after being handcuffed to some ducting on top of the building, uses a hacksaw to *cut off his hand.*

He had a hacksaw! Why didn't he cut through the handcuff chain? Or the metal rod the other cuff was attached to? 

Has there ever been a reason given as to why he had to cut off his hand instead of the handcuff? Maybe in the comics or commentary or something?