42 CFR § 84.178 - Breath response type, airflow resistance test—PAPR classes HE and PAPR100.

Resistance to airflow will be measured with a breathing machine as described in § 84.88.

(a) Minimum inhalation resistance must be greater than zero mm of water-column height.

(b) Maximum exhalation resistance must be less than 89 mm of water-column height.