HEPA 20 cartridge filter

HEPA 20 air cartridge filters are miscellaneous items that can be found and utilized in Fallout: New Vegas.

Characteristics
These cartridges can be found in Vault 22, within a locker on the oxygen recycling level. The locker can only be accessed by the cave deeper down in Vault 22, the door that had directly lead to it, is now blocked by unmovable debris. Once located and picked up, the cartridges can be used to repair the air filtration system at the Brotherhood of Steel's hidden bunker in Hidden Valley, for the Still in the Dark quest.

Location
Specifically to locate the HEPA filters, go to the fifth floor of Vault 22, and take the stairs to the next level. Here a room is found, that leads back up to another section of the third floor. Open the door to the cave, then find a wooden door saying "oxygen recycling". The HEPA filters are located in a locker in the upper right corner of the room.