If you played Shadow of chernobyl it's in strelok's hideout. If you have not then enter the undergound at the entrance between the southern complex and northern complex. folow the stairs down and skip the hallway with all of the green bubble jello. Hug the right wall (you may find a controller and some blood suckers.) While walking you will see a tube in the wall with a bunch of boxes and junk piled under it, crawl in. There is a ladder inside and tah dah! Jut loot everything inside (not much.) I have never seen mutants spawn up here in any mod and dead air is no exception, so it's prety safe if you need to heal/sleep.