(a) The complete gas mask will be fitted to the faces of persons having varying facial shapes and sizes. (b) Where the applicant specifies a facepiece size or sizes for the gas mask, together with the approximate measurements of faces they are designed to fit, the Institute will insure that test subjects suit such facial measurements. (c) Any gas mask parts which must be removed to perform the facepiece or mouthpiece fit test shall be replaceable without special tools and without disturbing the facepiece or mouthpiece fit. (d) The facepiece or mouthpiece fit test, using positive or negative pressure recommended by the applicant and described in his instructions will be used before each test specified in paragraph (e) of this section, and in §84.125. (e)(1) Each wearer will enter a chamber containing 100 p.p.m. isoamyl acetate vapor for a half-mask facepiece and 1,000 p.p.m. isoamyl acetate vapor for a full facepiece or mouthpiece. (2) The facepiece or mouthpiece may be adjusted, if necessary, in the test chamber before starting the tests. (3) Each wearer will remain in the chamber for 8 minutes while performing the following activities: (i) Two minutes, nodding and turning head; (ii) Two minutes, calisthenic arm movements; (iii) Two minutes, running in place; and (iv) Two minutes, pumping with a tire pump into a 28 liter (1 cubic foot) container. (4) Each wearer shall not detect the odor of isoamyl acetate during the test.

Any references to STPs do not indicate a requirement or a specific standard to which all respirators must comply. They denote a test procedure that NIOSH uses in their own testing and certification of RPD. There may exist other test procedures that manufacturers use prior to submitting respirators for NIOSH approval.