The leak-tightness of the facepiece and the pressure drop on inspiration and, in the case of the filtering devices, purification capacity must keep contaminant penetration from a polluted atmosphere low enough not to be prejudicial to the health or hygiene of the user.
Caithfidh teinne ligin na haghaidhmhíre agus an titbhrú ionanálaithe agus, ó thaobh na ngléasanna scagtha, an toilleadh íonaithe, treá truaillithe ó atmaisféar truaillithe a choinneáil íseal go leor sa chaoi nach ndéantar dochar do shláinte ná do shláinteachas an úsáideora.