National Institute for Occupational Safety and Health

National Personal Protective Technology Laboratory 

Procedure No. TEB-APR-STP-0003 Revision: 2.5 Date: 27 January 2023

DETERMINATION OF EXHALATION RESISTANCE TEST,

AIR-PURIFYING RESPIRATORS

STANDARD TESTING PROCEDURE (STP)

1. PURPOSE

This document establishes the procedure for ensuring that the performance exhibited by airpurifying respirators (APRs) submitted for Approval, Extension of Approval, or examined during

Certified Product Audits, meets the minimum exhalation resistance requirements set forth in 42

CFR, Part 84, Subpart I, Section 84.122; Subpart K, Section 84.172; Subpart L, Section 84.203;

the Statement of Standard for Chemical, Biological, Radiological and Nuclear (CBRN) FullFacepiece Air-Purifying Respirator (APR) Revision 2 dated 4-4-2003; and the Statement of

Standard for Chemical, Biological, Radiological and Nuclear (CBRN) Air-Purifying Escape

Respirator (APER) dated 9-30-2003.

2. GENERAL

This standard testing procedure (STP) describes the determination of exhalation resistance for

APRs 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/MATERIAL

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

3.1.1. An anthropometric headform or fixture on which to mount the complete 

respirator assembly in the configuration as worn by the user. In addition, fixtures 

are required for mounting a canister only when testing full facepiece APR for 

CBRN and for mounting mouthpiece respirators. 

3.1.2. A means of connecting the headform or test fixture to the flow controller. The 

respirator must be fitted to the fixture with no leaks.

3.1.3. Compressed air source capable of delivering a minimum of 85 liters per minute 

(lpm). 

3.1.4. Setra Datum 2000 Model 239 digital manometer, or equivalent, with an accuracy 

of ± 0.01%R ± 1 digit. Connect manometer to a pressure tap on the line between

the flow controller and headform or test fixture with mounted respirator. 

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

and Read-out Unit model 0154, or equivalent, with an accuracy +/- 0.70%R +/- 

0.20% f.s. 
Procedure No. TEB-APR-STP-0003 Revision: 2.5 Date: 27 January 2023 Page 2 of 6 

3.1.6. Rope caulk, glue gun with hot-melt glue and beeswax as needed 

3.1.7. Heating plate, beaker, and small brush as needed

4. TESTING REQUIREMENTS AND CONDITIONS

Prior to beginning any testing, confirm that 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. Follow individual instruction manuals for set up and maintenance of equipment used in 

this procedure prior to beginning any testing. Malfunctioning equipment must be 

repaired or replaced and properly set up and calibrated before starting all tests.

5.2. Turn on the airflow and set flow controller to 85 lpm, tolerance +/- 1.4 lpm.

5.3. Insert the connection of the headform or test fixture to the connection of the resistance 

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

5.4. Disconnect the headform or test fixture from the resistance tester and mount the 

respirator facepiece on the headform or fixture. Filtering facepiece respirators are sealed 

using hot melt glue and beeswax on a flat plate with a joint for connection to the 

resistance apparatus. For CBRN air purifying escape respirators, spread the elastomeric 

neck dam, and pull the hood over the headform. The neck dam should seal tightly around 

the neck of the headform. Mouthpiece type respirators require a special adapter. 

Elastomeric half mask and full-facepiece respirators are carefully mounted on the 

headform to ensure good contact around the entire sealing flange. Rope caulk can be 

used to help seal the critical area around the nose and / or chin for half masks. Be careful 

not to block the mouth of the headform with the chin cup of full facepieces. For each 

particular model, the size that fits the standard headform best should be used. Other 

headforms from different manufacturers are available in the lab to obtain a better seal on 

a particular facepiece if problems are encountered in obtaining a good seal.

5.5. Insert the connection of the headform or test fixture to the connection of the resistance 

tester.

5.6. Read resistance in inches of water to the nearest hundredth of an inch on the digital 

manometer. Convert inches to millimeters by multiplying by 25.4.

5.7. Record the measurement.

5.8 Perform the test on three samples.
Procedure No. TEB-APR-STP-0003 Revision: 2.5 Date: 27 January 2023 Page 3 of 6 

6. PASS/FAIL CRITERIA

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

84.122, Subpart K, Section 84.172, Subpart L, Section 84.203; the Statement of Standard 

for Chemical, Biological, Radiological and Nuclear (CBRN) Full-Facepiece, AirPurifying Respirator (APR) Revision 2 dated 4-4-2003, and the Statement of Standard for

Chemical, Biological, Radiological and Nuclear (CBRN) Air-Purifying Escape 

Respirator (APER) dated 9-30-2003. 

6.2. The maximum allowable resistance requirements for gas masks are as follows.

Maximum Exhalation Resistance

[Millimeter water column] 

Type of gas mask Initial Final1

Front-mounted or back-mounted (without particulate filter) 20 20

Front-mounted or back-mounted (with approved particulate 

filter)

20 20

Chin-style (without particulate filter) 20 20

Chin-style (with approved particulate filter) 20 20

Escape (without particulate filter) 20 20

Escape (with approved particulate filter) 20 20

1

Measured at end of the service life specified in Tables 5, 6, and 7 of this subpart. 

6.3. The resistance for non-powered air-purifying particulate respirators upon initial 

exhalation shall not exceed 25 mm water column height pressure.

6.4. The maximum allowable resistance requirements for chemical cartridge respirators are as 

follows. 

Maximum Exhalation Resistance

[Millimeter water column]

Type of chemical-cartridge respirator Initial Final 1

Other than single-use vinyl chloride respirators: 

For gases, vapors, or gases and vapors 20 20

For gases, vapors, or gases and vapors, and particulates 20 20

Single-use respirator with valves: 

For vinyl chloride 20 20

For vinyl chloride and particulates 20 20

Single-use respirator without valves: 

For vinyl chloride 15 20

For vinyl chloride and particulates 25 40

1 Measured at end of service life specified in Table 11 of this subpart.
Procedure No. TEB-APR-STP-0003 Revision: 2.5 Date: 27 January 2023 Page 4 of 6 

6.5. The maximum allowable resistance requirements for tight-fitting powered air-purifying 

respirators (PAPR) are as follows:

Maximum Exhalation Resistance

[Millimeter water column] 

Type of tight-fitting PAPR Initial Final 1

With HE particulate filter(s) only 20 20

With chemical cartridge(s) and HE particulate filter(s) 20 20

With chin-style canister and HE particulate filter 20 20

With front or back mounted canister and HE particulate 

filter

20 20

1

 Measured at end of silica dust test specified in section 84.179 

6.6. The maximum allowable resistance requirements for CBRN full facepiece APRs are as 

follows. 

Maximum Exhalation Resistance

[Millimeter water column]

CBRN full facepiece air-purifying respirators Initial Final 1

Chin style 20 20

Non-facepiece mounted 20 20

1 Measured at end of service life

6.7. For CBRN air-purifying escape respirators (APER), the exhalation resistance prior to 

environmental conditioning shall not exceed 20 mm water column. 

7. RECORDS/TEST SHEETS

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

reported as shown in attached example data sheet.

8. ATTACHMENTS

8.1. Attachment A: Sample Exhalation Resistance Test Data Sheet
Procedure No. TEB-APR-STP-0003 Revision: 2.5 Date: 27 January 2023 Page 5 of 6 

Attachment A: Sample Exhalation Resistance Test Data Sheet
Procedure No. TEB-APR-STP-0003 Revision: 2.5 Date: 27 January 2023 Page 6 of 6 

Revision History

Revision Date Reason for Revision

1.0 7 March 2004 Historic document

1.1 3 June 2005 Update header and format to reflect lab move from Morgantown, 

WV

No changes to method

2.0 30 March 2009 Significant rewrite of RCT-APR-STP-0003. Document name 

changed to TEB-APR-STP-0003. Changes affect form and provide 

clarification of technical content.

-Addition of alternate method using digital manometer and mass

flowmeter

-Addition of precision and accuracy data for standard and alternate

methods

-New tables added for clarification, removal of obsolete respirator

types and incorporation of CBRN APR, APER and industrial PAPR

types

-New instructions on fitting respirators to headforms and fixtures

-Specifications added to equipment list

2.1 27 September 2011 Update description of mass flow controller called out in 3A1.5. 

Formatting check for web accessibility

2.2 19 September 2012 Review and editing for accuracy, no technical changes

2.3 25 March 2014 Modified specification in sections 5.6 and 5.A.4 from “flat 

aluminum plate” to “flat plate”. Editorial change to section 6.1.

2.4 15 March 2019 -Section 3, Updated list of equipment to recognize use of mass flow

meter and electronic, digital manometer (formerly called out as an

alternate procedure).

-Section 4, Updated to current laboratory standards omitting P and

A exercise, and practices for lab safety in favor of those employed

by the lab.

-Section 5, Eliminate information on procedure using old

instruments, essentially adopting the “Alternate Procedure”

identified in rev 2.3 as the standard procedure. Also, eliminated

requirement for, and use of dry test meter.

-Section 6, Reformatted and normalized tables used to

communicate the pass/fail values for the various classes of

respirators.

2.5 27 January 2023 Removed references to Subpart KK. Other sections were updated

with minor editorial formatting, including the sample test data 

sheet.