Respirators are required for humans to breathe the toxic atmosphere on Euphrosyne, otherwise one might become feral. In an unfiltered environment, a person must sleep with a respirator on.
Because most post-war structures feature airlocks, respirators are typically removed indoors so people can eat and socialize. Notably, gorillas and other wildlife do not require them, as they have naturally adapted to the toxic air.
Almost all respirators are manufactured post-war by various cultures, including the Remnant, Scavengers, Clans, and Mechanics. Post-war HMC also produces respirators for their captive humans. Militaries and combat troops occasionally use specialized respirators that hook up directly to blush gas canisters, allowing soldiers to quickly inhale the combat stimulant in the heat of battle.
There are some exceptions that date back to before or during the war: Vanguard gas masks and respirators, civilian farming respirators from pre-war RS-1 (some produced by HMC, others by the residents themselves), and custom or scavenged respirators made by early Sludge exiles.