There were very mature and reliable technologies on the production of air circulation devices and cartridges. Even in the Great Dark Age tens of thousands of years ago, people had been roaming in space on the starships that boasted air circulation magical equipment.
No matter how technologies declined in the ten thousand years of warfare, this most fundamental technology was never lost. Even the Star Glory Federation at the edge of the cosmos had developed it to such a high level that the gigantic air circulation system in the space fortresses could provide fresh air for millions of people at the same time.
The technologies of the Imperium of True Human Beings were at least decades more advanced than those of the Star Glory Federation. They certainly had more knowledge about air circulation too.
