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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-0106 Revision: 1.2 Date: 10 June 2021

DETERMINATION OF INHALATION AIRFLOW RESISTANCE, PRESSURE-DEMAND,

TYPE C AND CE, SUPPLIED-AIR RESPIRATORS

STANDARD TESTING PROCEDURE (STP)

1. PURPOSE

This test establishes the procedures for ensuring the airflow resistance requirements for a Type C

and CE, Demand and Pressure-Demand, Supplied-Air Respirators meet the minimum

performance requirements set forth in 42 CFR, Part 84, Subpart J, Section 84.157(a)(b).

2. GENERAL

This STP describes the Determination of Inhalation Airflow Resistance, Pressure-Demand, Type

C and CE, Supplied-Air Respirators 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. A 300 cubic foot gas cylinder of compressed air or equivalent.

3.1.2. A Helicoid calibrated pressure gauge and connecting fittings or equivalent.

3.1.3. Air regulator, Model 8, from Matheson Gas Products or equivalent.

3.1.4. National Instruments NI USB-9215A Portable USB-Based DAQ with 

Simultaneous Sampling; LabVIEW 2013; Dell Optiplex 755 Personal Computer, 

SCBA test software 

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

air flows - Model SR-085 or equivalent. 

3.1.6. Temperature compensated pressure transducer (Validyne Engineering Model No. 

DP45) or equivalent.

3.1.7. Mechanical breather with 622 kg. m/min. cam as per U.S. B. of M. drawings C1748 (3/l7/69) breathing machine and B-1198 (3/6/69) breathing cam or 

equivalent.

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

Indiana or equivalent.
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Procedure No. RCT-ASR-STP-0106 Revision: 1.2 Date: 10 June 2021 Page 2 of 7 

3.1.9. Setra Datum 2000 Model 239 digital manometer – accuracy: ± 0.01%R ± 1 digit, 

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

5.1. Perform pre-test balancing of transducer and recording system.

5.1.1. Connect the transducer to be used during testing in parallel with a manometer. 

Attach the manometer and transducer to a pressure regulated air supply. A pinch 

clamp, used for slight pressure changes, is placed in-line with two equal lengths 

of tubing for the manometer and transducer connections. An alternate method to 

generate low pressures for calibration is to use the Dwyer model A-396A 

calibration pump or equivalent.

5.1.2. Connect the transducer cable to the CD-19A demodulator, and then connect the 

demodulator to the National Instruments DAQ. The DAQ is then connected to 

the PC via USB port. Turn the system on and press the Calibration button. After 

the calibration screen appears, with no load applied to the transducer, press the 

Zero button to set the zero-pressure point.

5.1.3. Apply a pressure of 0.5 inches of water to the transducer/manometer system. 

Check that the demodulator reads 0.5 inches, and adjust if necessary. Then check 

that the waveform displayed is at 0.5 inches, and adjust the LabVIEW readout if 

necessary.

5.1.4. Repeat step 5.1.3 with the pressures of 1.0, 1.5, and 2.0 inches of water until each 

pressure point reads correctly on the waveform. No adjustments should be 

necessary at this point.

5.1.5. Verify that the pressures are correct, by applying pressures for 1.5, 0.5 and 0.0 

inches of water in descending order ensuring each pressure point reads correctly 

on the waveform. If adjustments are necessary, then repeat the calibration 

process for all pressures.

5.1.6. After the calibration sequence is complete, remove the pressure source from the 

system.

5.2. Assemble the apparatus as shown in Figure 1. Mount the pressure transducer where 
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Procedure No. RCT-ASR-STP-0106 Revision: 1.2 Date: 10 June 2021 Page 3 of 7 

shock and vibration are minimal.

5.3. Mount facepiece on anthropometric head, taking care not to block resistance port below 

and left of nose, particularly if a nosecup is used. 

5.4. Connect regulator or breathing tube to facepiece. Do not connect head to breathing 

machine. Turn on breathing machine and use a timer to determine that the cam is 

operating at 24 rpm. (This will give a 40 lpm volume). When calibrated, turn breathing 

machine off.

5.5. Assemble respirator using maximum hose length. Connect the anthropometric head with

the facepiece to the breathing machine.

5.6. Turn on the air supply to the respirator and set it to the minimum specified pressure.

5.7. Turn on breathing machine for three complete cycles to obtain inhalation resistance. (See 

Data Analysis). Then turn off breathing machine but leaving the air pressure turned on.

5.8. With the air supply pressure still turned on connect transducer port from head-form to a

manometer to obtain static pressure in facepiece.

5.9. Repeat steps 5.6 thru 5.9 with minimum hose length and maximum pressure. 

5.10. When testing has been completed, shut off breathing machine and air supply pressure, 

and disconnect transducer from head.

5.11. Data Analysis

5.11.1. Take the peak values of the inhalation readings from the LabVIEW system and 

read resistance in inches of water column height. 

5.11.2. For pressure-demand units the inhalation resistance cannot fall below the zeropressure baseline. A negative spike is allowed as long as there is no area 

between the point where the spike goes negative and the point where it returns to 

positive.

Note: This test should be done on a minimum of two respirators, or more if additional testing is

required (42 CFR, Part 84, Sections 84.12, 84.30, and 84.60).

6. PASS\FAIL CRITERIA

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

84.157(a)(b). 

 Reference. 

84.157 Airflow resistance test; Type C supplied-air respirator, pressure-demand class; 

minimum requirements.
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Procedure No. RCT-ASR-STP-0106 Revision: 1.2 Date: 10 June 2021 Page 4 of 7 

(a) The static pressure in the facepiece shall not exceed 38 mm. (1.5 inches) of watercolumn height.

(b) The pressure in the facepiece shall not fall below atmospheric at inhalation airflows

less than 115 liters (4 cubic feet) per minute.

7. RECORDS\TEST SHEETS

7.1. Record the test data in a format that shall be stored and retrievable. Data to be reported as 

shown in attached data sheet. 
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Procedure No. RCT-ASR-STP-0106 Revision: 1.2 Date: 10 June 2021 Page 6 of 7 

Figure 1: Breathing Machine Set-up 
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Procedure No. RCT-ASR-STP-0106 Revision: 1.2 Date: 10 June 2021 Page 7 of 7 

Revision History

Revision Date Reason for Revision

1.0 23 May 2001 Historic document

1.1 27 September 2005 Update header and format to reflect lab move from Morgantown, 

WV. No changes to method

1.2 10 June 2021 Updated NIOSH Logo. Updated test procedure and figures to 

reflect new PC based recording system using LabVIEW, and other 

procedural changes related to calibration.