Lol yes I was joking. I had a friend over and we were having a laugh seeing how many prisoners can you fit into a 5x5 holding cell. Honestly, I don't know. And I like crushing walls! No one said (apart from when the CEO rings and never hangs up, making me mute volume as it was getting annoying) I had to run the prison well.
As for using non lethal knockout gas, or proper lethal gas, that is inspired by the fortress series of films. One of them was set on a spaceship, or was it an asteroid? Either way that means that the air could be vented out of sections, either deliberatly, or accidentially from a meteorite impact.
I'm not looking to make real life comparisons because prisons are a boring place full of mad, bad and sad people. Personally, I'm fond of this man

Who's name is John Howard. He had this bright idea that if you didn't treat prisoners like shit, like not playing games with them (like, how long can you leave someone in a holding cell, whilst in full view of the reception staff doing fuck all and laughing. Or testing the fire alarms at 2 in the morning, getting a lot of prisoners banging on their doors and telling them to keep quiet, once a month to name two) , they'd start to feel like human beings and all those problems that culminated with them ending up in prison they can finally get some help for.
But, like simcity, sure it's nice to build a good, well running city with all the amenities, but it's also super fun to send in tornadoes, ufo's and riots.