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 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. (ENT: "Sleeping Dogs")
The first use of the decon chamber aboard Enterprise came in 2151, when Commander Trip Tucker and Vulcan Subcommander 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")
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")
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. Season 2's "A Night in Sickbay" featured a bizarre decon scene with Sato, T'Pol, Archer, and his dog and "Bounty" highlighted a B-story set within decon. By the final season of Enterprise, however, the crew of the NX-01 went through decon fully clothed.