This key is found in the second-floor break room of the dead factory. This key does not change it's name after checking.
This key can open the door in the facility corridor that leads to the Treatment Control Room. Closed door reads "TREATMENT CONTROL ROOM. It's closed." This door will be closed only in that case, if Jill has pushed Nemesis off the bridge during their last encounter. In other ways, the door can just be unlocked from the other side.
Also, this key can be used for opening the weapon locker in the basement. But before, the plastic card attached to the key must be processed by the ultraviolet machine in the Water Purification Room.
When changed, the plastic card has another painting. Also, after checking a new message can be read "The plastic card is radiating. It seems to show some kind of code pattern.".
Ultraviolet machine reads the message initialy: "Ultraviolet rays are applied to the water. There's a tiny slot where a plastic card could fit."
And the weapon locker reads next message: "It is closed with a sturdy-looking door. There's a tiny slot where a plastic card could fit.".
After opening the weapon box, this item disappears without warning.