StacksVerified U.S. regulatory reference

42 CFR §84.90

Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗
  1. (a)Resistance to inhalation airflow will be measured in the facepiece or mouthpiece while the apparatus is operated by a breathing machine as described in § 84.88.
  2. (b)The inhalation resistance of open-circuit apparatus shall not exceed 32 mm. (1.25 inch) water-column height (at a flow rate of 120 liters per minute).
  3. (c)The inhalation resistance of closed-circuit apparatus shall not exceed the difference between exhalation resistance (§ 84.91(e)) and 10 cm. (4 inches) water-column height.