National Institute for Occupational Safety and Health

National Personal Protective Technology Laboratory 

Procedure No. RCT-APR-STP-0005-05a-06 Revision: 3.1 Date: 27 January 2023

DETERMINATION OF QUALITATIVE ISOAMYL ACETATE (IAA)

FACEPIECE FIT, AIR-PURIFYING RESPIRATORS

STANDARD TESTING PROCEDURE (STP) 

1. PURPOSE

This document establishes the procedure for ensuring that the level of protection provided by the

Isoamyl Acetate facepiece fit test requirements on air-purifying respirators (APRs) submitted for

Approval or Extension of Approval meet the minimum certification standards set forth in 42 CFR

Part 84, Subpart G, Section 84.63(a)(c), Subpart I, Section 84.124, Subpart K, Section 84.176,

and Subpart L, Section 84.205.

2. GENERAL

This standard testing procedure (STP) describes the determination of qualitative isoamyl acetate

(IAA) facepiece fit test 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. Large viewable chamber with interlocking double doors and exhaust system, 

approximately 9.7' x 12.2' x 8' in size.

3.1.2. Tire pump 

3.1.3. Isoamyl acetate, 99%.

3.1.4. Tiered wick

3.1.5. Graduated cylinder, 100 mL 

3.1.6. Sliding measurement calipers, Seritex model GPM 104, 0-200 mm length, as 

shown in Attachment A, Figure 1. 

3.1.7. Spreading measurement calipers, Seritex model GPM 106, 0-300 mm width, as 

shown in Attachment A, Figure 2. 

3.1.8. Facepiece, mouthpiece, hood, or helmet equipped with a cartridge or canister 

with organic vapor protection.

4. TESTING REQUIREMENTS AND CONDITIONS
Procedure No. RCT-APR-STP-0005-05a-06 Revision: 3.1 Date: 27 January 2023 Page 2 of 13

4.1. Prior to beginning any testing, all measuring equipment to be used must have 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 the International System of Units (SI) when available. 

4.2. General facepiece fit test requirements for gas mask, chemical cartridge, mouthpiece, 

and powered air-purifying respirators with chemical cartridges or canisters. 

4.2.1. The fit test shall be performed using a panel of test subjects of various facial 

sizes measured according to the NIOSH Bivariate Panel (NIOSH Panel) 

requirements. The measured face length and face width are used to designate 

the subject’s NIOSH Panel cell number, as illustrated in Attachment B. 

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. Prior to fit testing, test subjects shall be subjected to the odor threshold 

screening as follows: 

4.2.2.1. Prepare a stock solution by adding 1 ml isoamyl acetate to 800 ml of 

distilled water and shake for 30 seconds. This solution is stable for two 

days. 

4.2.2.2. To a 1 liter volumetric add 0.4 ml stock solution to 500 ml distilled

water. To an identical volumetric add 500 ml distilled water. Mark both 

samples with an identifying marker known only to the test operator. The 

solutions must be made fresh daily.

4.2.2.3. The following instructions shall be typed on a card and placed on the 

table in front of the two test jars (i.e. 1 and 2): “The purpose of this test 

is to determine if you can smell banana oil at a low concentration. The 

two bottles in front of you contain water. One of these bottles also 

contains a small amount of banana oil. Be sure the covers are on tight, 

and then shake each bottle for two seconds. Unscrew the lid of each 

bottle, one at a time, and sniff at the mouth of the bottle. Indicate to the 

test operator which bottle contains banana oil.” 

4.2.2.4. If the test subject correctly identifies the jar containing the odor test 

solution, the subject shall continue with the fit testing. 

4.2.2.5. The screening shall be conducted in an isoamyl acetate free 

environment. 

4.2.3. Any respirator part which must be removed to perform the facepiece or 
Procedure No. RCT-APR-STP-0005-05a-06 Revision: 3.1 Date: 27 January 2023 Page 3 of 13

mouthpiece fit test shall be replaceable without special tools and without 

disturbing the facepiece or mouthpiece fit.

4.2.4. Each wearer shall enter the chamber containing 100 ppm isoamyl acetate for 

half-mask respirators and 500 ppm for full facepieces, mouthpieces, hoods, and 

helmets.

4.2.5. The respirator or mouthpiece may be adjusted, according to the manufacturer’s 

User Instructions (UI), prior to entering the chamber, if necessary; however, 

upon entry into the test chamber the facepiece or mouthpiece shall not be readjusted. 

4.2.6. If a respirator is supplied with multiple facepiece sizes, a test subject may only 

achieve a pass in one size, except when testing an extra-small or extra-large 

facepiece, in accordance with 4.3.2. 

4.2.7. If a test subject is unable to achieve a user seal check after three donning 

attempts, it is considered a failed test; however, if the facepiece model comes in 

multiple sizes, they may attempt to don an alternate size.

4.2.8. If a test subject is able to achieve the required user seal checks; but, prior to 

starting the test, the subject detects the IAA, the subject shall be removed to an 

IAA-free atmosphere and permitted to don the respirator again. After two

attempts the test is considered a failure. However, if the facepiece model comes 

in multiple sizes they may attempt to don an alternate size.

4.3. Test subject selection

4.3.1. For respirators designed and manufactured in one, two or three unique facepiece 

sizes, the fit test will be conducted with 18 individual test subjects using the 

NIOSH Panel (Attachment B). See Table 1 for the suggested test subject 

distribution in relation to the NIOSH Panel (NIOSH is allowing flexibility in the 

use of subjects from well-populated panel cells. NIOSH will attempt to test at 

least one subject from each cell, but no more than four subjects may be tested per 

cell).
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Table 1: Suggested test subject distribution to be used for Isoamyl Acetate fit testing in 

relation to the NIOSH Panel 

NIOSH Panel – Cell Number Number of Test Subjects

1 1

2 1

3 2

4 4

5 1

6 1

7 4

8 2

9 1

10 1

4.3.1.1. For respirators designed and manufactured in one unique size, a subject 

failing to achieve a pass is considered a test failure. 

4.3.1.2. For respirators designed and manufactured in two unique sizes: 

4.3.1.2.1. Subjects in panel cells 1-4 and cell 6 shall be tested first 

wearing the smaller sized respirator. If the subject does not 

pass in the smaller sized respirator, the subject can be tested 

again wearing the larger sized respirator. 

4.3.1.2.2. Subjects in panel cells 7-10 and cell 5 shall be tested first 

wearing the larger sized respirator. If the subject does not 

pass in the larger sized respirator, the subject can be tested 

again wearing the smaller sized respirator. 

4.3.1.2.3. A subject failing to achieve a pass in either of the sizes 

available for testing is considered a failure.

4.3.1.3. For respirators designed and manufactured in three unique sizes: 

4.3.1.3.1. Subjects in panel cells 1 and 2 shall be tested wearing the 

smaller size initially.

4.3.1.3.2. Subjects in panel cells 3-7 shall be tested wearing the 

regular/medium size initially.

4.3.1.3.3. Subjects in panel cells 8, 9, and 10 shall be tested wearing the 

larger size initially.

4.3.1.3.4. If a subject does not pass in the first respirator size, the 

subject will be retested in the next available size. A subject 

failing in the smaller sized respirator, can try the medium, and 
Procedure No. RCT-APR-STP-0005-05a-06 Revision: 3.1 Date: 27 January 2023 Page 5 of 13

then larger sized respirator. A subject failing in the medium 

sized respirator can try the smaller and larger sized 

respirators. A subject failing in the larger sized respirator can 

try the medium, then the smaller sized respirator. A subject 

failing to achieve a pass in any of the sizes available for 

testing is considered a failure. The Test Administrator may 

determine whether or not the third test is worthy of 

completion. If the subject failed to achieve a pass in the small 

and medium sized respirator, trying the large may not be 

necessary since the large may be too big for the subject. If 

the subject failed to achieve a pass in the large and medium 

sized respirator, trying the small may not be necessary since 

the small may be too small for the subject. 

4.3.2. For respirators designed and manufactured with four or five unique facepiece 

sizes, the fit-test panel will be comprised of 21 and 24 members respectively, 

representing the NIOSH Panel, (Attachment B). No more than four subjects 

may be tested per cell. Four individual test failures will be allowed; the number 

of test failures is not increased with the increased number of test subjects.

4.3.2.2. Subjects in panel cells 1 and 2 shall be tested wearing the small size 

first.

4.3.2.3. Subjects in panel cells 3-7 shall be tested wearing the regular/medium 

size first.

4.3.2.4. Subjects in panel cells 8, 9, and 10 shall be tested wearing the large size 

first.

4.3.2.5. For each additional size facepiece, such as an extra-small (XS) or extralarge (XL), there will be an additional 3 subjects tested. 

4.3.2.5.1. Testing an additional size designated as extra-small shall 

include testing an additional three subjects from panel cells 1-

3 and must include one positive test utilizing a subject from 

panel cell 1. If three subjects from cell 1 are unable to pass 

the XS, the project will be denied. 

4.3.2.5.2. Testing an additional size designated as extra-large shall 

include testing an additional three subjects from panel cells 5-

10 and must include one positive test utilizing a subject from 

panel cell 10. If three subjects from cell 10 are unable to pass 

the XL, the project will be denied. 

4.3.2.6. If a subject does not pass in the first respirator size, the subject will be 

retested in the next available size, reference 4.3.1.3.4 if more detail is

required. 
Procedure No. RCT-APR-STP-0005-05a-06 Revision: 3.1 Date: 27 January 2023 Page 6 of 13

5. PROCEDURE

5.1. Follow individual instruction manuals if any, for set up, calibration, 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. Determine the amount of isoamyl acetate required to produce the concentration desired 

according to the size and volume of the test chamber using the following formula.

C = V ⊗ 22.4 Τ 760

MW 273 P x106 

 Vt 

Where: V = volume in ml of isoamyl acetate required in ml

C = concentration in ppm of isoamyl acetate desired in chamber 

MW = molecular weight of isoamyl acetate

T = chamber temperature in degrees Kelvin 

P = chamber pressure (760 mm Hg)

⊗ = density of isoamyl acetate in g/ml 

Vt = volume of chamber in liters

5.2.1. For the NIOSH test chamber: using the graduated cylinder, distribute onto the 

tiered wick 16 ml isoamyl acetate for half mask respirators or 80 ml isoamyl 

acetate for full facepiece, hoods, helmets and mouthbit respirators.

5.3. Allow 20 minutes for equalization of the concentration in the chamber.

5.4. In an isoamyl acetate free environment, allow the test subject to read the manufacturers 

donning instructions and perform positive or negative user seal check procedures. 

5.5. The test subject will don the respirator and perform a user seal check per the 

manufacturer's UI. If the test subject cannot obtain a successful user seal check, he/she 

will not be sent into the chamber. Upon obtaining a successful user seal check, the 

subject will enter the chamber. 

5.6. For all IAA fit tests, the test subject shall enter the test chamber and remain in the test 

chamber for 8 minutes while performing the following activities:

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

5.6.2. Two (2) minutes callisthenic arm movements.

5.6.3. Two (2) minutes running in place.
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5.6.4. Two (2) minutes pumping with tire pump. 

5.7. The test subject must not detect the odor of IAA when they enter the chamber and 

perform the required exercises. If on initial entry into the IAA chamber, the subject 

immediately (before the required exercises begin) detects the odor of IAA, the subject 

will immediately exit the chamber, adjust the respirator, perform a second user seal 

check, and if successful, re-enter the chamber. 

5.8. Upon completion of the above activities the test subject will exit the chamber and 

verbally notify the Test Administrator as to the performance of the respirator with any 

remarks pertinent to the fit or performance of the respirator.

5.9. If the subject detects the banana type odor of isoamyl acetate during any exercise they 

will indicate a thumbs down motion and will be removed from the chamber. Once 

removed, a user seal check will be performed and the facepiece harness or tension 

mechanism will be checked for their tightness. 

6. PASS/FAIL CRITERIA

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

84.63(a)(c), Subpart I, Section 84.124, Subpart K, Section 84.176, and Subpart L, 

Section 84.205. 

6.2. The number of test failures will not exceed four. 

6.3. If an overall pass is achieved, but three subjects report the same issue about the comfort 

of the facepiece, the test will be considered a failure.

7. RECORDS/TEST SHEETS

7.1. All test data collected will be recorded on the appropriate Determination of Qualitative 

Isoamyl Acetate (IAA) Facepiece Fit IAA Test data sheet (Attachment D). 

8. ATTACHMENTS

8.1. Attachment A: Figures 

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

8.3. Attachment C: Anthropometric Measurements 

8.4. Attachment D: Sample Facepiece Fit IAA Test Data Sheet
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8.1 Attachment A: Figures

Figure 1: Sliding Calipers 

Figure 2: Spreading Calipers 

Figure 1: Sliding Calipers 
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Figure 2: Spreading Calipers 
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8.3 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. RCT-APR-STP-0005-05a-06 Revision: 3.1 Date: 27 January 2023 Page 11 of 13

8.2 Attachment C: Anthropometric Measurements

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.
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8.4 Attachment D: Sample Facepiece Fit IAA Test Data Sheet
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Revision History

Revision Date Reason for Revision

February 1996 NIOSH has reduced the IDLH for isoamyl acetate in the Pocket Guide 

to Chemical Hazards from 3000 ppm to 1000 ppm. This resulted in the 

NIOSH STP being run at the IDLH concentration contrary to good 

work practices, and OSHA standards which stipulate the 

“concentrations during the test shall not exceed an OSHA permissible 

exposure limit, the ACGIH threshold limit values, or any known 

recommended exposure limit, when there is no OSHA PEL or ACGIH 

TLV, and not create a health or physical hazard for the test subject or 

operator.” In the face of these facts, the test concentration was reduced 

to the OSHA PEL and NIOSH REL of 500 ppm with commitment to 

revisit the appropriateness of the test, and of isoamyl acetate as the test 

agent of choice in future regulation change modules.

1.0 16 January 2002 Historic document

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

No changes to method

2.0 20 March 2008 Correct errors in sections 4.3.3.2 and 5.2 and update to reflect new file

naming procedures and changes announced in Letter to All 

Manufacturers dated 18 May 2005.

3.0 20 December 2018 Changes throughout the document to incorporate a new 

anthropometric panel referred to as the NIOSH Panel.

3.1 27 January 2023 Subpart KK references were removed. Editorial updates were made 

throughout the procedure, including to the Attachments.