There should be a system in place to evacuate the guards and gas the entire prison. I'm sure the former exists, hold they all get out in time.
gas needs to be disbursed strategically depending on the incident, the location of inmates etc. Can’t just send it through a system or vent. Not as effective. In a disturbance or riot there are usually many inmates not involved or in separate areas doing nothing wrong. Lastly such a system would be cost prohibitive.
BTW I was 90 days on the job nightman on a living unit, 1971 Dec 26. 2 hours before I came in they used the most gas ever inside building in Calk history more than when mere locked the door on the students at Berkeley and sent massive amounts of gas inside.