Worn over the nose, mouth and chin and held on by elasticised straps over the ears, this face-mask, of a clear material, is connected to an Oxygen container or Oxygen diffusing device worn on the belt.  The respirators have communicators built in, which override the use of cap microphones if caps are also worn.  For example, when Captain Scarlet was wearing his Respirator but his cap mike was never used when talking to Colonel white.  Neither was Lieutenant Green's when talking to Scarlet whilst wearing his cap.  (The two events occurred in episode 5, "Avalanche").