. >> donald avila is serving a four-month sentence for parole violation. >> just a bunch of guys livingher. somebody's going to get on your nerves, and you're going to get on somebody's nerves one of these days, you know what i mean? >> inmate johnson recalls his first experience with prison violence after going to general population, commonly referred to as the main line. >> when i hit the main line, maybe about like two weeks -- not even a good two weeks, a big riot jumped off, and i saw a lot of stickings and everything, and there was this -- it was crazy. >> we do have a lot of blind spots, making it a little difficult as far as observation if, in fact, when something happens such as a riot or we have some type of altercation. the officers at the end of the tiers for visibility, but it still makes it difficult for observations, especially 150 yards down the tiers. >> sergeant rudy carmella supervises cellblock 5, one of the oldest operating prison structures in the united states. >> to walk up to a cell, to look -- to see what is going on, you have to sometimes look inside. so it pu