This unit will not provide protection against gases, mists, or vapors which poison through skin absorption (such as hydrocyanic acid gas). Impermeable protective clothing providing whole body coverage is required where exposure to such agents is possible. Users with certain physical characteristics (such as beards, sideburns, hollow temples, deep skin creases, etc.) may not obtain a satisfactory face seal against the facepiece skirt, resulting in outward air leakage and diminished service time. Addi¬tional information on respirator fitting and testing may be found in American National Standards Institute (ANSI) specification Z88.2.