42 CFR § 84.181
Communication performance test—PAPR class PAPR100
June 11, 2020
(a) Powered air-purifying respirators must be designed to allow for proper communication while worn.
(b) A Modified Rhyme Test7 will be used to test the wearer's ability to communicate efficiently.
7The Modified Rhyme Test is used in speech intelligibility experiments. See https://www.nist.gov/ctl/pscr/modified-rhyme-test-audio-library.
(c) The communications requirement is met if the overall performance rating is greater than or equal to 70 percent.