It’s the ‘based on the work schedule’ part that stops most second jobs. I don’t know if the fire department follows the same plan as the police, four days on, three days off, but I believe it does. There aren’t that many second jobs that allow a person to work a different set of days every week of the year (including Saturday and Sunday.) And of course mandatory overtime days adds to the problem. Same problem in a different way applies for teachers. Their ‘summer’ starts a couple weeks after summer jobs open up and ends a couple weeks prior the close of summer. That doesn’t translate into too many opportunities. (Oh, for those not aware, teachers are not paid by the school district for summer months.)