When I was working for Austin Fire, the police dept bought a bunch of K cars. With the Texas heat, there was a problem that them running the cars 24 hours straight (three shifts) the catalytic converter would start a smoldering fire in the carpet padding under the back seat. I made, I think, three calls on that. No idea how many total problems APD had.
My dad bought a 1975 Chevy Nova, first car we had with a cat. The dealer would warn people who bought them not to let it idle for any length of time if they were parked 8n tall grass, particularly in the summer for that very reason.