Respiration devices are apparatuses used to supplement the air an individual breaths.
Benzites are apparently unable to breathe a standard oxygen/nitrogen atmosphere, and therefore had to wear respiration devices in those environments during the early 2360s. By the early 2370s, however, they had fallen into disuse. (TNG: "Coming of Age"; DS9: "The Ship")
- It has never been clearly stated in dialogue what the respiration devices worn by the Benzites were truly used for or what happened to them. It's a safe assumption, though, that technological advances between TNG's "A Matter of Honor" and DS9's "The Ship" caused them to become obsolete.