42 C.F.R. § 84.172 – Airflow resistance test.

(a) Resistance to airflow will be measured in the tight-fitting respiratory inlet covering of a complete particulate respirator mounted on a test fixture with air flowing at continuous rate of 85 ±2 liters per minute, before each test conducted in accordance with § 84.173.
(b) Resistance of a complete tight-fitting powered air-purifying particulate respirator system will be measured with the blower off if the manufacturer indicates that the respirator should not be doffed in the event of a blower failure.
(c) The maximum allowable resistance requirements for air-purifying particulate respirators are as follows:
Maximum Resistance[mm water-column height]
Respirator type Inhalation Exhalation
Initial Final
Non-Powered (N, R, and P) 35 N/A 25
Powered (tight fitting) (HE class and PAPR100 class) 50 70 20

Respirator type	Inhalation	Exhalation
Initial	Final
Non-Powered (N, R, and P)	35	N/A	25
Powered (tight fitting) (HE class and PAPR100 class)	50	70	20