National Institute for Occupational Safety and Health 

National Personal Protective Technology Laboratory

Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024

DETERMINATION OF RESPIRATOR FIT, QUANTITATIVELY USING CORN OIL AEROSOL, 

FOR POWERED AIR-PURIFYING RESPIRATORS WITH LOOSE- OR TIGHT-FITTING 

RESPIRATORY INLET COVERINGS, STANDARD TESTING PROCEDURE 

1. PURPOSE

This document establishes the procedure by which a generated corn oil aerosol is used for 

determining if powered air-purifying respirators (PAPRs) incorporating loose- or tight-fitting 

respiratory inlet coverings submitted for Approval, Extension of Approval, or examined during 

Certified Product Audits meet the minimum certification standard set forth in 42 CFR Part 84, 

Subpart K, Section 84.176. 

2. GENERAL

This standard testing procedure (STP) describes the named procedure in sufficient detail that a 

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

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

record of those results, reporting the measurements obtained in a preestablished, standard format. 

3. EQUIPMENT/MATERIALS 

3.1. Rear Light Scattering Laser Photometer: TSI Inc., model 8587A, or equivalent. 

Concentration range is 1.0 micrograms per cubic meter (μg/m3

) to >200 milligrams per 

cubic meter (mg/m3

). 

3.2. NIOSH Dynamic Fit Software: Custom software developed in the LabVIEW 

environment, or equivalent. Software is available from NIOSH or Data Science 

Automation. 

3.3. Aerosol Generator: MSP, model 2045 High Output Aerosol Generator, or equivalent. 

Capable of maintaining 5 to 100 mg/m3 of corn oil challenge aerosol concentrations with 

a Mass Median Aerodynamic Diameter (MMAD) of 0.4 to 0.6 micrometers (μm). 

3.4. Aerosol Monitor: TSI Inc., DustTrak II Aerosol Monitor model 8530, or equivalent. 

Detection range of 0.001 to 400 mg/m3 with resolution of ± 0.1 percent (%) of reading or 

± 0.001 mg/m3

, whichever is greater. 

3.5. Corn Oil, 99% pure. CAS Number 8001-30-7. Commercial product names are 

Maise/Maize Oil, Maydol, and Mazola Oil, or equivalent. 

3.6. Scanning Mobility Particle Sizer (SMPS): TSI Inc., with models 3082 Electrostatic 

Classifier (EC), 3081A Long Differential Mobility Analyzer (DMA), 3752 HighConcentration Condensation Particle Counter (CPC), and 3088 Advanced Aerosol 

Neutralizer, or equivalent. 

3.7. Aerosol Test Chamber: The chamber shall be designed and constructed so that the test 

participants have ample space for unobstructed movement during the test and are visible 
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 2 of 15

at all times while in the chamber. The chamber shall have an air handling unit to provide 

a consistent and uniform aerosol concentration and fresh air, and may include mixing 

fans. The chamber design should include an entry vestibule designed to allow safe entry 

and exit from the chamber with minimal disturbance to both the aerosol concentration 

and the concentration uniformity. All tubing shall be conductive and tubing lengths and 

bends should be minimized. 

3.8. Chamber Communications: Generic brand and model. Electronic audio communications 

(i.e., loudspeaker) for real-time voice communication from test administrator to test 

participants. 

3.9. Tire Pump: Generic brand and model. Hand operated floor style tire pump that is 

approximately 20 inches (in.) tall with an approximately 15 in. stroke. 

3.10. Face Size Sliding Measurement Caliper: Seritex, model GPM 104, or equivalent. With 

range of 0-200 millimeters (mm). 

3.11. Face Size Spreading Measurement Caliper: Seritex, model GPM 106, or equivalent. With 

range of 0-300 mm.

3.12. Facepiece Direct Probe: Custom probe developed by NIOSH, or equivalent. The basis of 

design was first described by Liu [AIHAJ (45); 278-283, 1984]. The design shall not 

interfere with the fit or function of the PAPR. The probe is a bulkhead fitting and 

provides a tight seal using two rubber washers, one metal washer, and one nut. See 

Attachment A.

4. TESTING REQUIREMENTS AND CONDITIONS

4.1. Prior to beginning any testing, all measuring equipment to be used shall have been 

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

All measuring equipment utilized for this testing should have been calibrated using a 

method traceable to the National Institute of Standards and Technology (NIST), when 

available.

4.2. General fit test requirements for PAPRs 

4.2.1. The fit test shall be performed using a group of test participants of various face 

sizes. Face size is determined from the NIOSH Bivariate Panel (NIOSH Panel) as 

illustrated in Attachment B. The measured face width and face length of each test 

participant are used to designate the test participant’s NIOSH Panel cell number.

4.2.1.1. Face Width is the Bizygomatic Breadth measurement (Attachment C), 

using the spreading measurement calipers.

4.2.1.2. Face Length is the Menton-Sellion measurement (Attachment C), using 

the sliding measurement calipers.

4.2.2. The PAPR shall be adjusted according to the applicant’s User Instructions (UI)

prior to entering the chamber. Upon entry into the test chamber, the inlet 

covering shall not be re-adjusted.
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 3 of 15

4.2.3. If a PAPR is supplied with multiple inlet covering sizes, to achieve a test 

participant pass, each test participant is required to achieve a success in any one 

size, except when testing an extra-small or extra-large inlet covering, in 

accordance with 4.3.3.1.4. 

4.2.4. For tight-fitting PAPR:

4.2.4.1. Any PAPR part which must be removed to perform the user seal check 

shall be replaceable without special tools and without disturbing the 

inlet covering on the test participant’s face.

4.2.4.2. If the test participant is unable to achieve a user seal check after three 

donning attempts, it will be deemed a trial failure. If the applicant has 

provided the PAPR in multiple sizes, the test participant may attempt 

to don an alternate size inlet covering.

4.3. Test participant selection and testing panel composition requirements

4.3.1. NIOSH is allowing flexibility in the selection of test participants. NIOSH will 

attempt to select a panel that contains at least one face size representative from 

each panel cell. No more than four test participants may be from any single panel 

cell. See Table 1 for the suggested face size distribution in relation to the NIOSH 

Panel (Attachment B).

Table 1: Recommended face size distribution to be used for fit testing in relation to the NIOSH Panel 

4.3.2. For PAPRs designed and manufactured with one, two, or three inlet covering

sizes, the fit test will be conducted with 18 test participants which are selected to 

represent the NIOSH Panel (Attachment B).

4.3.2.1. For PAPRs designed and manufactured in one unique inlet covering 

size, a test participant failing to achieve a trial pass is deemed a test 

participant failure.

4.3.2.2. For PAPRs designed and manufactured in two unique inlet covering

sizes:

NIOSH Panel – Cell Number Number of Face Size Representatives

1 1

2 1

3 2

4 4

5 1

6 1

7 4

8 2

9 1

10 1
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 4 of 15

4.3.2.2.1. Test participants from panel cells 1-4 and cell 6 shall be 

tested wearing the smaller size inlet covering initially.

4.3.2.2.2. Test participants from panel cells 7-10 and cell 5 shall be 

tested wearing the larger size inlet covering initially.

4.3.2.2.3. If a test participant does not achieve a trial pass in the first 

inlet covering size evaluated, the test participant may be 

asked to conduct additional trials in the alternate size.

4.3.2.2.4. The outcome of a test participant failing to achieve at least 

one trial pass with either of the available inlet covering

size options is deemed a test participant failure. 

4.3.2.3. For PAPRs designed and manufactured in three unique inlet covering

sizes:

4.3.2.3.1. Test participants from panel cells 1 and 2 shall be tested 

wearing the smaller size initially.

4.3.2.3.2. Test participants from panel cells 3-7 shall be tested 

wearing the regular/medium size initially.

4.3.2.3.3. Test participants from panel cells 8-10 shall be tested 

wearing the larger size initially.

4.3.2.3.4. If a test participant does not achieve a trial pass in the first 

inlet covering size evaluated, the test participant may be 

asked to conduct additional trials in the next available 

size(s). For example:

A test participant failing to achieve a trial pass in the 

smaller sized inlet covering may then proceed to trials with

the medium size and, if necessary, the larger size inlet 

covering.

A test participant failing to achieve a trial pass in the 

medium sized inlet covering may then proceed to trials 

with the smaller size and, if necessary, the larger size inlet 

coverings.

A test participant failing to achieve a trial pass in the larger 

size inlet covering may then proceed to trials with the 

medium size and, if necessary, the smaller sized inlet 

covering.

The test administrator may have discretion with additional

size trials. Additional size trials may not be necessary if 

the available inlet covering size is obviously inappropriate 

for the test participant. 
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 5 of 15

4.3.2.3.5. The outcome of a test participant failing to achieve at least 

one trial pass with any of the available inlet covering size 

options is deemed a test participant failure. 

4.3.3. For PAPRs designed and manufactured with four or five unique inlet covering 

sizes, the fit-test will be conducted with 21- or 24- test participants, respectively, 

representing the NIOSH Panel (Attachment B). 

4.3.3.1. For PAPRs designed and manufactured in four or five unique inlet 

covering sizes: 

4.3.3.1.1. Test participants from panel cells 1 and 2 shall be tested 

wearing the small size initially. 

4.3.3.1.2. Test participants from panel cells 3-7 shall be tested 

wearing the regular/medium size initially. 

4.3.3.1.3. Test participants from panel cells 8-10 shall be tested 

wearing the large size initially. 

4.3.3.1.4. For each additional size inlet covering, such as an extrasmall (XS) or extra-large (XL), three (3) additional test 

participants shall be required. 

4.3.3.1.4.1. Testing an additional size designated as extrasmall shall include testing an additional three test 

participants from panel cells 1-3. At least one test 

participant must be from panel cell 1. 

4.3.3.1.4.2. Testing an additional size designated as extra-large 

shall include testing an additional three test 

participants from panel cells 5-10. At least one test 

participant must be from panel cell 10. 

4.3.3.1.5. If a test participant does not achieve a trial pass in the first 

inlet covering size evaluated, the test participant may be 

asked to conduct additional trials in the next available 

size(s). See section 4.3.2.3.4 for further guidance. 

4.3.3.1.6. The outcome of a test participant failing to achieve at least 

one trial pass with any of the available inlet covering size 

options is deemed a test participant failure. 

5. PROCEDURE

NOTE: Reference Section 3 for equipment, model numbers, and manufacturers. 

Equipment should be operated and calibrated in accordance with the manufacturer’s 

operation and maintenance manual(s), or the laboratory’s quality management system. 

5.1. Aerosol Test Chamber Set-up 
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 6 of 15

5.1.1. Power on photometers, SMPS, and aerosol monitor and allow to warm up 

following the manufacturer’s instructions.

5.1.2. Power on chamber air handling unit (exhaust), aerosol generators, and chamber 

mixing fans.

5.1.2.1. Adjust mixing fans to create an even distribution of aerosol particles 

throughout the chamber, while avoiding high airflows and turbulent 

air.

5.1.2.2. Adjust chamber air handling unit speed and aerosol generator pressure 

to balance the chamber flow and establish a corn oil challenge 

concentration. Corn oil challenge concentration is measured by the 

aerosol monitor.

5.1.2.2.1. Establish a corn oil challenge concentration of 30 to 40 

mg/m3

.

5.1.3. Allow a minimum of 30 minutes for the aerosol test chamber corn oil challenge 

concentration to stabilize.

5.1.4. Use the SMPS to measure the aerosol particle size.

5.1.4.1. The size required is 0.4 to 0.6 μm with a geometric standard deviation 

of less than 2.0 MMAD.

5.1.5. Use the aerosol monitor to periodically measure the aerosol test chamber corn oil 

challenge concentration prior to and during each trial. Adjust concentration if 

necessary.

5.2. Donning of the PAPR

5.2.1. The inlet covering shall be minimally modified for the installation of the 

facepiece direct probe. The installation shall not interfere with the fit or function 

of the PAPR. The probe should be positioned in the oral/nasal region of the 

PAPR. Each probe is sealed against in the inlet covering using two rubber 

washers, one metal washer, and one nut.

5.2.2. The UI provided by the applicant shall be reviewed by the test administrator and 

test participant. Test participant training will be conducted by the test 

administrator per the applicant’s UI. Test participants will be instructed, when 

applicable, on the applicant’s size selection, donning, head-harness tightening, 

suspension adjustment, positive and negative pressure user seal checks, doffing,

and accessory interfacing as specified by the UI.

5.2.3. Each test participant shall perform an unassisted donning of the PAPR. Donning 

shall be supervised by the test administrator.

5.2.3.1. The test administrator is permitted to make the appropriate adjustments 

to the inlet covering until the test administrator is satisfied that the test 
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 7 of 15

participant is wearing the PAPR in compliance with the applicant’s UI.

5.2.3.2. Expert donning is not allowed. The test administrator or other parties 

are not allowed to put the PAPR on the test participant.

5.2.4. Test participants will don the PAPR and it will be set to the lowest userselectable speed setting.

5.3. Conducting the Corn Oil Test

5.3.1. Test participants shall enter the aerosol test chamber through the enclosed

vestibule area to minimize disruptions to the aerosol challenge concentration. 

Only one door may be open at a time. Once the test participant is in the chamber,

they will be instructed to attach their sample line tubing to an assigned 

photometer.

5.3.2. The photometer will measure the corn oil challenge concentration in the chamber 

at the start of each trial.

5.3.3. The photometer will continuously measure the corn oil breakthrough 

concentration in the oral/nasal region of the PAPR during the trial.

5.3.4. The NIOSH Dynamic Fit software will be used to record raw data from the 

photometer and continuously generate a fit factor throughout each exercise and 

trial. The fit factor value is updated approximately once per second. The fit factor 

calculation is described in Attachment D.

5.3.5. A trial consists of a set of four two-minute standard exercises. During the trial, 

each test participant will perform the following four exercises, for two minutes

each, in the sequence listed below. The test administrator will give verbal 

commands to stop and start each exercise.

Two (2) minutes nodding up and down and turning head side to side.

Two (2) minutes calisthenic arm movements.

Two (2) minutes running in place.

Two (2) minutes pumping with tire pump.

5.3.5.1. Test participants should not touch any portion of the PAPR during any 

part of the testing exercises.

5.3.6. The test administrator will identify a pass/fail result for each test participant

exercise and trial.

5.3.7. After the completion of a trial, test participants will be instructed to disconnect 

the sample line from the photometer and exit the chamber through the vestibule 

area.
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 8 of 15

5.3.7.1. For trials identified as passing, the test participant may be instructed to 

doff the PAPR.

5.3.7.2. For trials identified as failing, the test administrator shall conduct a 

failure analysis to confirm or reject the failing result. The test 

participant may be instructed to leave the PAPR donned. If necessary, 

the test administrator will examine the PAPR in the donned 

configuration. The test administrator will instruct the test participant to 

doff the PAPR when their review is complete. 

5.3.8. Comments and observations by test participants are voluntary. All pertinent 

comments and observations shall be recorded by the test administrator. Care must 

be taken to ensure test participant comments are understood and accurately

recorded. 

6. PASS/FAIL CRITERIA

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

84.176. 

6.2. For tight-fitting full facepiece PAPR, to achieve a test participant pass: 

6.2.1. The fit factor must meet or exceed 500 throughout the entire trial.

6.3. For tight-fitting half mask PAPR, to achieve a test participant pass:

6.3.1. The fit factor must meet or exceed 100 throughout the entire trial.

6.4. For loose-fitting inlet covering PAPR, to achieve a test participant pass:

6.4.1. The fit factor must meet or exceed 500 throughout the entire trial.

6.5. The number of test participant failures may not exceed four. The outcome of five or more 

test participant failures is deemed an overall test failure.

6.6. Special considerations for PAPR with an extra-small inlet covering: 

6.6.1. The outcome of no test participants from panel cell 1 passing in accordance with 

4.3.3.1.4.1 is deemed an overall test failure.

6.6.2. The outcome of three (3) test participants from panel cell 1 failing in accordance 

with 4.3.3.1.4.1 is deemed an overall test failure. 

6.7. Special considerations for PAPR with an extra-large inlet covering: 

6.7.1. The outcome of no test participants from panel cell 10 passing in accordance 

with 4.3.3.1.4.2 is deemed an overall test failure. 

6.7.2. The outcome of three (3) test participants from panel cell 10 failing in 

accordance with 4.3.3.1.4.2 is deemed an overall test failure. 
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 9 of 15

6.8. If an overall pass is achieved, but three test participants report the same issue about the 

comfort of the PAPR, the outcome is deemed an overall test failure. 

7. RECORDS/TEST SHEETS

7.1. All test data collected will be recorded on the appropriate fit test data sheet

(Attachment E). 

8. LIST OF ABBREVIATIONS AND ACRONYMS

Table 2: List of Abbreviations and Acronyms Used Within This Document 

9. ATTACHMENTS

9.1. Attachment A: NIOSH Facepiece Direct Probe 

9.2. Attachment B: NIOSH Bivariate Panel (NIOSH Panel)

9.3. Attachment C: Anthropometric Measurements Reference

9.4. Attachment D: Fit Factor Calculations

9.5. Attachment E: Example Data Sheet - PAPR Corn Oil Fit Test Data Sheet

Abbreviation 

or Acronym

Definition

NIOSH National Institute for Occupational Safety and Health

NPPTL National Personal Protective Technology Laboratory

PAPR powered air-purifying respirator

STP standard testing procedure

CFR Code of Federal Regulations

μg/m3 micrograms per cubic meter

mg/m3 milligrams per cubic meter

MMAD Mass Median Aerodynamic Diameter

μm micrometers

% percent

SMPS Scanning Mobility Particle Sizer

EC Electrostatic Classifier

DMA Differential Mobility Analyzer

CPC Condensation Particle Counter

in. inch

mm millimeter

UI user instructions

XS extra-small

XL extra-large
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 10 of 15

Attachment A: NIOSH Facepiece Direct Probe
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 11 of 15

Attachment B: NIOSH Bivariate Panel (NIOSH Panel)

9

NIOSH Panel

98.5

108.5

128.5

118.5

138.5

Face Length (mm)

1

3 4

2

5

6

7 8

10

120.5 132.5 144.5 158.5

Face Width (mm)

Face Width (mm)

120.5 134.5 146.5 158.5
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 12 of 15

Attachment C: Anthropometric Measurements Reference

Description Definition Diagram

Bizygomatic 

Breadth

Maximum horizontal 

breadth of the face as 

measured with a 

spreading caliper between 

the zygomatic arches.

Menton–

Sellion 

Length

Distance as measured 

with a sliding caliper in 

the midsagittal plane 

between the menton 

landmark and the sellion 

landmark.
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 13 of 15

Attachment D: Fit Factor Calculations

The PAPR performance is quantitatively determined in terms of a fit factor (FF). The fit factor is 

determined by the ratio of the corn oil challenge concentration in the chamber ([Cch]) to the corn oil 

breakthrough concentration in the oral/nasal region of the PAPR ([CPAPR]). Under the conditions of the 

test and the sensitivity of the photometer, the maximum fit factor that can be reported is 100,000. 

FFFF =

[CCcch]

[CCPPPPPPPP]
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 14 of 15

Attachment E: Example Data Sheet - PAPR Corn Oil Fit Test Data Sheet
Procedure No. NPPTL-APR-STP-0009-0010 Revision: 1.0 Date: February 12, 2024 Page 15 of 15

Revision History

Revision Date Reason for Revision

0.0 16 March 2020 Original release

1.0 12 February 2024 CVB-APR-STP-0009 and CVB-APR-STP-0010 have been combined 

into a single procedure and renumbered as 

NPPTL-APR-STP-0009-0010. Document has been revised for 

clarity.