---
kind: "section"
citation: "42 C.F.R. § 84.90"
title: "42"
number: "84.90"
heading: "Breathing resistance test; inhalation."
url: "https://uscodex.org/cfr/42/84.90"
---

# §84.90. Breathing resistance test; inhalation.

- (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](/cfr/42/84.88.md).
- (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).
- (c) The inhalation resistance of closed-circuit apparatus shall not exceed the difference between exhalation resistance ([§ 84.91(e)](/cfr/42/84.91.md?p=e)) and 10 cm. (4 inches) water-column height.

## Notes

### Authority

Authority: 29 U.S.C. 651 et seq.; 30 U.S.C. 3, 5, 7, 811, 842(h), 844.

### Source

Source: 60 FR 30355, June 8, 1995, unless otherwise noted.