The decontamination chamber (or simply decon chamber) was a facility on Earth Starfleet vessels (such as NX-class starships) in the mid-22nd century.
Decon was used for decontaminating crewmembers after exposure to the potentially dangerous environmental conditions, lifeforms, materials, airborne bodies, or other contaminants found in alien environments such as planets or spacecraft. Aboard NX-class ships, decon was located adjacent to the launch bay and a locker room. It was not much larger than a turbolift, featuring two benches and a window looking out into a corridor. Utilizing a combination of ultraviolet radiation and various topical skin gels to achieve its effect, the chamber offered very little privacy, requiring officers to disrobe and remain in the cramped chamber for sometimes extended periods. While the decon chamber was inordinately small, Enterprise armory officer Malcolm Reed likened it to a spa he once visited in Mexico. (ENT: "Broken Bow", "Sleeping Dogs", et al.) The decon chamber was located on D Deck of an NX-class starship. (ENT: "Bounty")
The first use of the decon chamber aboard Enterprise NX-01 came in 2151, when Commander Trip Tucker and Vulcan Sub-Commander T'Pol were exposed to protocystian spores after visiting a trading complex on Rigel X. (ENT: "Broken Bow")
In the year 2152, Tucker was protected from a sedative gas released by Ferengi pirates while enduring an overextended stay in decon and was therefore the only crewmember left conscious during the initial stages of that crisis. (ENT: "Acquisition")
The same year, a group of three Takret – Rellus Tagrim, Renth, and Guri – passed the decon chamber before being welcomed aboard the ship by Captain Jonathan Archer. (ENT: "The Catwalk")
In 2153, T'Pol suggested placing a pair of Borg-assimilated Tarkaleans into the decon chamber, but Doctor Phlox dimissed this suggestion because he was unable to examine them there as extensively as he could in sickbay. (ENT: "Regeneration")
In 2154, Enterprise crewmembers Hoshi Sato and Charles Tucker were confined to the decon chamber after becoming infected with a silicon-based virus. While the chamber was locked to prevent the exposure of the entire crew, Sato managed to break the lock and escape during a fever-induced hallucination. This resulted in the immediate lockdown of that entire deck. (ENT: "Observer Effect")
In the mirror universe, the crew of the ISS Enterprise held a Tholian prisoner in their decon chamber, using the device to torture and ultimately kill the alien in 2155. (ENT: "In a Mirror, Darkly")
By the 23rd and 24th centuries, the decontamination chamber became obsolete aboard Federation vessels, as transporter biofilters and advanced shipboard ventilation systems ruled out the necessity for such a device. (TNG: "Realm Of Fear")
The decon chamber was one of the more salacious aspects of the premiere of Star Trek: Enterprise, clearly intended to showcase both the lesser technology of the NX-01 and the heightened sex appeal of the new series. Though several nearly-nude scenes took place within the decon chamber over the course of the series, none quite reached the risqué level of its first appearance. second season's "A Night in Sickbay" featured a bizarre decon scene with Sato, T'Pol, Archer, and his pet dog Porthos, and "Bounty" highlighted a B-story set within decon. By the fourth season of Enterprise, the crew of the NX-01 went through decon fully clothed.
Enterprise's decon chamber was built as a set on Paramount Stage 18.