---
kind: "section"
citation: "42 C.F.R. § 84.91"
title: "42"
number: "84.91"
heading: "Breathing resistance test; exhalation."
url: "https://uscodex.org/cfr/42/84.91"
---

# §84.91. Breathing resistance test; exhalation.

- (a) Resistance to exhalation airflow will be measured in the facepiece or mouthpiece of open-circuit apparatus with air flowing at a continuous rate of 85 liters per minute.
- (b) The exhalation resistance of demand apparatus shall not exceed 25 mm. (1 inch) water-column height.
- (c) The exhalation resistance of pressure-demand apparatus shall not exceed the static pressure in the facepiece by more than 51 mm. (2 inches) water-column height.
- (d) The static pressure (at zero flow) in the facepiece shall not exceed 38 mm. (1.5 inches) water-column height.
- (e) Resistance to exhalation airflow will be measured in the facepiece or mouthpiece of closed-circuit apparatus with a breathing machine as described in [§ 84.88](/cfr/42/84.88.md), and the exhalation resistance shall not exceed 51 mm. (2 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.