Wow! A subject I know something about!
I took a job as a PO and to put it mildly, run for the hills. It is disgusting. Assume Every job will carry the risk of exposure to Hep A,B and C. Assume HIV and anything else scary. Add to that pee and poop rubbed over the walls and that's what wrecked prison cells look like. There is also the real chance that you could be exposed to many types of drug residue, You will risk taking a trip on bath salts like a number of officers I served with did after touching it during a cell search.
Also, please factor in the huge amount of time you'll waste at the gates and as landings are locked to allow you to work. If you worked 8 hours on site expect two going through searches and waiting for escorts.
Unless you are getting huge money, avoid it if you can.
jo