A sealed room next to sickbay aboard Enterprise NX-01 where returning landing parties are held under ultraviolet light and apply decontamination gel until Doctor Phlox clears them.
In the 22nd century transporters have no biofilters and are seldom used for people, so crew coming back from an alien world may carry unknown organisms. The decon chamber is the answer: a small locked compartment bathed in blue light where those exposed strip to their underclothes and rub a medicated gel on to one another while Phlox watches the scans.
It is introduced in Broken Bow with a scene between T'Pol and Trip Tucker, and returns often in Enterprise, for example in Sleeping Dogs and in Acquisition, where being shut inside spares Tucker when Ferengi raiders gas the ship.
In Observer Effect, Tucker and Hoshi Sato are confined there with a lethal silicon-based virus while non-corporeal aliens observe how the humans respond.