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User seal check
Also called a fit-check. In this procedure, the user performs a simple maneuver to determine if the seal is adequate in an approximate, qualitative fashion. For example, the user may obstruct the inlet ports and attempt to inhale; passage of air implies that there is significant leakage at the facial sealing surface. The individual performs this type of assessment each time he or she dons a mask.
A probe inside the mask measures leakage of a marker material placed in the surrounding air. It requires the assistance of a trained industrial hygienist or someone with equivalent technical skills. It is generally not feasible with single use/ disposable respirators.
A substance such as saccharin or Bitrex (an extremely bitter compound) is sprayed into the air, and the user is asked whether he or she detects it.