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National Institute for Occupational Safety and Health

National Personal Protective Technology Laboratory 

626 Cochrans Mill Road 

Pittsburgh, PA 15236

Procedure No. RCT-ASR-STP-0122 Revision: 1.2 Date: 12 May 2020

DETERMINATION OF EXHALATION BREATHING RESISTANCE - OPEN-CIRCUIT, DEMAND 

AND PRESSURE-DEMAND, SELF-CONTAINED BREATHING APPARATUS

STANDARD TESTING PROCEDURE (STP)

1. PURPOSE

This test establishes the procedures for ensuring that the exhalation breathing resistance

requirements for an Open-Circuit, Demand and Pressure-Demand, Self-Contained Breathing

Apparatus (SCBA) meet the performance requirements set forth in 42 CFR, Part 84, Subpart H,

Section 84.91(a)(b)(c)(d).

2. GENERAL

This STP describes the Determination of Exhalation Breathing Resistance - Open-Circuit,

Demand and Pressure-Demand, Self-Contained Breathing Apparatus test in sufficient detail that a

person knowledgeable in the appropriate technical field can select equipment with the necessary

resolution, conduct the test, and determine whether or not the product passes the test.

3. EQUIPMENT/MATERIALS

3.1. The list of necessary test equipment and materials follows:

3.1.1. Dwyer Slant Manometer 0-3", F. W. Dwyer Manufacturing Co., Michigan City, 

Indiana or equivalent. 

3.1.2. Setra Datum 2000 Model 239 digital manometer with an accuracy of ±0.04%R 

±1 digit or equivalent.

3.1.3. ISI Anthropometric Test heads with tube for measuring breathing resistance and 

air flows - Model SR-085 or equivalent. 

3.1.4. Brooks Instrument Co. model 5853S Mass Flow Controller with Brooks Control 

and Read-out Unit model 0154 – accuracy ±0.70%R ±0.20% f.s or equivalent.

4. TESTING REQUIREMENTS AND CONDITIONS

4.1. Prior to beginning any testing, all measuring equipment employed has been calibrated in

accordance with the testing laboratory’s calibration procedure and schedule. All 

measuring equipment utilized for this testing must have been calibrated using a method 

traceable to recognized international standards when available.

5. PROCEDURE
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Procedure No. RCT-ASR-STP-0122 Revision: 1.2 Date: 12 May 2020 Page 2 of 5 

5.1. Assemble unit as per manufacturer's instructions.

5.2. Mount facepiece on an anthropometric head and check for leakage. Block outlet of head 

with rubber stopper.

5.3. Turn on cylinder then connect resistance port to slant manometer. Wait for the reading to 

stabilize. This reading is the static pressure.

5.4. Ensure the positive pressure source has been calibrated at a flow of 85 ± 1.4 lpm. 

5.5. Insert the connection of the headform to the connection of the positive pressure source, 

without the respirator mounted. Set the manometer to read zero. 

5.6. Disconnect the headform from the positive pressure source and mount the respirator 

facepiece on the headform. 

5.7. To measure the exhalation resistance, insert the connection of the headform to the 

connection of the positive pressure source. 

5.8. Read the exhalation resistance in inches of water directly from the manometer.

5.9. Data Analysis.

5.9.1. Record readings on test data sheets.

5.9.2. The exhalation resistance shall not exceed 1.0 inches of water column height for 

demand units. 

5.9.3. The exhalation resistance shall not exceed the static pressure by more than 2.0 

inches of water column height. 

6. PASS\FAIL CRITERIA

6.1. The criterion for passing this test is set forth in 42 CFR, Part 84, Subpart H, Section 

84.91(a)(b)(c)(d). 

Reference: 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 
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Procedure No. RCT-ASR-STP-0122 Revision: 1.2 Date: 12 May 2020 Page 3 of 5 

inches) water-column height.

Note: See Test Procedure RCT-ASR-STP-0113 for additional testing requirements for SCBA 

with hoods. 

7. RECORDS\TEST SHEETS

7.1. All test data will be recorded on the BREATHING RESISTANCE TEST - 

EXHALATION, OPEN-CIRCUIT, SELF-CONTAINED BREATHING APPARATUS 

test data sheet.

8. ATTACHMENTS

8.1. Sample Data Sheet

8.1. Sample Data Sheet 
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Procedure No. RCT-ASR-STP-0122 Revision: 1.2 Date: 12 May 2020 Page 4 of 5 
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Procedure No. RCT-ASR-STP-0122 Revision: 1.2 Date: 12 May 2020 Page 5 of 5 

Revision History

Revision Date Reason for Revision

1.0 23 May 2001 Historic document

1.1 20 September 2005 Update header and format to reflect lab move from Morgantown, 

WV. No changes to method

1.2 12 May 2020 Updated NIOSH Logo. Updated Sections 3, 4, 5, and 6, with 

changes related to equivalent equipment, outdated pictures 

(removed), calibration requirements, and the procedure.