HEPA 20 cartridge filter

The HEPA 20 air cartridge filters are miscellaneous items in Fallout: New Vegas.

Characteristics
They can be found in Vault 22 in a locker on the oxygen recycling level. It can only be accessed by the cave in vault 22 because the door leading to it is blocked by debris. They are used for repairing the air filtration system in Brotherhood of Steel's hidden bunker in Hidden Valley for the Still in the Dark quest.

Location
To locate the HEPA filters go to the food production level and take the hallway straight down from the elevator. The hallway will force you to make a right, take the first door on your left and enter the small room with a terminal and steel door ( this door will require access from the overseers terminal to disengage the lock). There is also another way through a hole in one of the food production rooms, which leads to the cave, where you can find the wooden door. You will find you have entered a cave. Make the first available right and go up hill until you reach a worn wooden door to oxygen recycling. Upon entering the door make your way through the remainder of the tunnel until you reach a room. Head right in the room and you will see lockers lined up against the wall the HEPA filters are located in the locker to your far left.
 * There is a Vault 22 cave door keycard in the common area, it's on the bottom level, first door on the left side of the hallway that reads "quarters", it's on the shelf to your right when you open the door, there is a spore carrier brute asleep in the room, right in front of the door.