42 CFR § 84.90 - Breathing resistance test; inhalation.

---
identifier: "/us/cfr/t42/s84.90"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "42 CFR § 84.90 - Breathing resistance test; inhalation."
title_number: 42
title_name: "Public Health"
section_number: "84.90"
section_name: "Breathing resistance test; inhalation."
chapter_name: "PUBLIC HEALTH SERVICE, DEPARTMENT OF HEALTH AND HUMAN SERVICES"
subchapter_number: "G"
subchapter_name: "OCCUPATIONAL SAFETY AND HEALTH RESEARCH AND RELATED ACTIVITIES"
part_number: "84"
part_name: "APPROVAL OF RESPIRATORY PROTECTIVE DEVICES"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "29 U.S.C. 651  30 U.S.C. 3, 5, 7, 811, 842(h), 844."
regulatory_source: "60 FR 30355, June 8, 1995, unless otherwise noted."
cfr_part: "84"
---


# 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.

(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)) and 10 cm. (4 inches) water-column height.