National Institute for Occupational Safety and Health

National Personal Protective Technology Laboratory 

626 Cochrans Mill Road 

Pittsburgh, PA 15236

Procedure No. TEB-APR-STP-0052 Revision: 3.2 Date: 22 October 2019

DETERMINATION OF PARTICULATE FILTER EFFICIENCY LEVEL FOR P99

SERIES FILTERS AGAINST LIQUID PARTICULATES FOR NON-POWERED, AIRPURIFYING RESPIRATORS STANDARD TESTING PROCEDURE (STP)

1. PURPOSE

This procedure establishes the means for ensuring that the particulate filtering efficiency of P99

series filters used on non-powered respirators submitted for Approval, Extension of Approval, or

examined during Certified Product Audits, meets the minimum certification standards set forth in

42 CFR, Part 84, Subpart K, Section 84.181. These filters or filter cartridges may be integral to

respirator construction; mounted individually, or in sets of up to three; used in conjunction with

cartridges and canisters for chin-style, front-mounted, and back-mounted gas masks; or used in

combination with gas-and-vapor or atmosphere-supplying respirators.

2. GENERAL

This STP describes the test method to be used for the Determination of Particulate Filter

Efficiency Level for P99 Series Filters Against Liquid Particulates for Non-Powered, AirPurifying Respirators test in sufficient detail that a person knowledgeable in the appropriate

technical field can 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. TSI Model 8130 Automated Filter Tester or equivalent instrument - Air flow 

control accuracy is 2% of full scale. Pressure measurement accuracy is 2% of 

full scale. Penetrations can be measured to 0.001%, efficiencies to 99.999%.

3.1.2. Microbalance accurate to 0.0001 grams (g) 

3.1.3. Type A/E glass filters 102 mm diameter, high efficiency filters with a 1 

micrometer pore size

3.1.4. Timer (accurate to 0.01 percent) 
Procedure No. TEB-APR-STP-0052 Revision: 3.2 Date: 22 October 2019 Page 2 of 8

3.1.5. Dioctyl phthalate ((DOP, di(2-ethylhexyl)phthalate)) min. 98%

3.1.6. Respirator filter holder supplied for specific type which is compatible with TSI 

filter tester. NIOSH will not be obligated to use these holders for actual 

certification testing. All manufacturer test fixtures must be correlated with the 

NIOSH test method.

3.1.7. Thermal printer (supplied with TSI 8130) or optional data acquisition system

3.1.8. TSI, Green Line paper, part number 813010 - Lot number must be included on 

each box. Each lot must include the “Penetration vs. Resistance graph”.

4. TESTING REQUIREMENTS AND CONDITIONS

4.1. 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.

4.2. Respirator filters and filter cartridges shall be tested as follows.

4.2.1. The filtering elements of the respirator, including the filter holders and gaskets 

will be tested for particle penetration.

4.2.2. When filters are not separable from the respirator body, the exhalation valves 

will be sealed to ensure that any leakage due to the exhalation valve is not 

included in the filter penetration measurement.

4.2.3. Filters used in conjunction with gas mask canisters, and odd or unusually shaped 

filters may be tested on a headform assembly or test fixture provided by the 

applicant.

4.2.4. If a test fixture is supplied by the applicant, the test fixture shall have a serial 

number or other unique, easily referenced identifier permanently etched, 

engraved, or affixed.

5. PROCEDURE

Note: Where they have been developed to aid in the consistent operation of standard NIOSH 

test apparatus, work instructions are to be used.

5.1. Respirator filters will be challenged by a neat cold – nebulized DOP aerosol at 25 ±5 o

C 

that has been neutralized to the Boltzmann equilibrium state. The particle size 

distribution will be a count median diameter of 0.185 ± 0.020 micrometer and a 

geometric standard deviation not exceeding 1.6. Each respirator filter unit will be 

challenged with an aerosol concentration not exceeding 200 mg/m3

.
Procedure No. TEB-APR-STP-0052 Revision: 3.2 Date: 22 October 2019 Page 3 of 8

5.1.1. The DOP aerosol concentration will be determined daily by the following 

gravimetric method and calculated as milligrams per cubic meter (mg/m3

).

5.1.2. Weigh a 102 mm filter to the nearest 0.1 mg., mount in the gravimetric filter 

holder, subject it to the generated aerosol at 30 Lpm for 40 minutes , and reweigh 

the filter. Use a timer to monitor the duration of the test. Record the pre- and 

post-weights, time, and average flow rate on the data sheet and calculate the 

aerosol concentration in mg/m3 by the following formula:

Concentration in mg/m3 = W2 – W1

(Q / 1000) (T)

Where:

W1 = Initial filter weight in mgs.

W2 = Final filter weight in mgs.

Q = Flow rate in liters per minute

T = Elapsed time in minutes

With a flow rate of 30 Lpm for 40 minutes, the above formula simplifies 

to:

C = W2 – W1

1.2

5.1.3. Use the following formula to calculate the test duration:

T in minutes = (mg load) (1000 L / m3)

(C) (Q)

Where:

C = Concentration in mg/m3 from 5.1.2.

Q = Flow rate for test in Lpm

5.1.4. The upstream and downstream photometer readings are used for monitoring 

stability and for calculating a photometer correlation factor (CF). The correlation 

factor is determined with an empty filter holder and is calculated internally as 

shown below:

CF = Downstream Photometer Voltage – Downstream Background Voltage

Upstream Photometer Voltage – Downstream Background Voltage

The correlation factor is used by the software to express the upstream photometer 

signal in terms of the downstream photometer signal.

5.1.5. The DOP particle size distribution shall be verified using “green line” filter discs 

supplied by TSI with a known penetration range. Graphs of penetration vs. 

resistance for two sheets and five sheets of stacked filter discs are supplied with 

each lot of the standard filters, with a central line and upper and lower lines 

representing the expected penetration range at a given resistance. The test data 
Procedure No. TEB-APR-STP-0052 Revision: 3.2 Date: 22 October 2019 Page 4 of 8

should fall within an acceptance zone having boundaries defined by the upper 

and lower curves on the graphs. The standard filter test using both 2 sheets and 5 

sheets will be run at least once in each 8 hour test period to verify that the aerosol 

distribution is within the acceptance zone.

5.1.6. If the instantaneous filter penetration is not within the acceptance zone for any 

sample, abort testing and check the aerosol particle size with the TSI Green Line 

Paper.

5.2. Filters will be mounted and sealed on holders to prevent leakage around the filter holder. 

Single air purifying respirator filters will be tested at a challenge flow rate of 85

± 4 Lpm. Filters used as pairs on a respirator are tested using a single filter of the pair at 

42.5 ± 2 Lpm challenge flow rate. Filters used in threes are tested using a single filter of 

the set at 28.3 ± 1 Lpm challenge flow rate.

5.2.1. The challenge flow rate must be checked for stability for at least 30 seconds prior 

to testing.

5.3. A sample of 20 filter units will be tested against the DOP liquid aerosol. The filters shall 

be subjected to aerosol mass loading levels as shown in the table below. This is the mass 

amount of DOP aerosol that has contacted the filter.

Number of Filters in

Respirator Configuration

Initial Loading 

Level

Incremental 

Loading

Maximum 

Loading Level

Single 215 ± 5 mg. 30 ± 5 mg. 415 ± 5 mg.

Double 115 ± 5 mg. 30 ± 5 mg. 215 ± 5 mg.

Triple 85 ± 5 mg. 30 ± 5 mg. 155 ± 5 mg.

For P99 series filters, if the bandwidth (range) in penetration readings is equal to or less 

than 0.023% for the last 30 ± 5 mg at the initial loading level or within a subsequent 

incremental loading level, the filter passes the test. If the bandwidth in penetration 

readings is greater than 0.023% and not clearly decreasing, then the filter penetration is 

continuing to increase. The test is continued through the next 30 ± 5 mg of loading until 

the bandwidth in penetration readings is equal to or less than 0.023% for the incremental 

loading level, or the penetration level exceeds the maximum allowable level. The test is 

concluded and the filter is determined to fail the test if the bandwidth in penetration 

readings is greater than 0.023% for the last 30 ± 5 mg, ending at the maximum loading 

level indicated in the table above, or the maximum penetration exceeds 1.0 %.

5.3.1. If any one of the 20 filters has a penetration greater than 1.0 %, further testing of 

that filter will be terminated. Any filter that exceeds the specified limit shall be 

remounted and retested to ensure that leakage was not caused by a mounting 

leak. If retesting eliminates the excessive leakage, and testing has gone beyond 

the initial penetration, that sample will be considered an invalid sample and 

another tested in its place.

5.4. Determine and record on the data sheet the maximum filter penetration for each of the 20 

filters, and the bandwidth readings over the 30 ± 5 mg on which the “no further decrease 
Procedure No. TEB-APR-STP-0052 Revision: 3.2 Date: 22 October 2019 Page 5 of 8

in efficiency” determination is made or the initial unacceptable bandwidth readings.

6. PASS/FAIL CRITERIA

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

84.181.

6.2. The minimum efficiency for each of the 20 filters shall be determined and recorded and 

shall be equal to or greater than 99 %.

6.3. For the sample of 20 filters or filter cartridges to demonstrate acceptable performance, 

each filter shall meet or exceed the specified minimum efficiency level at the end point of 

the test, and the bandwidth of the last 30 ± 5 mg for each filter shall be less than or equal 

to 0.023% if not clearly decreasing, before the maximum loading level shown in section 

5.3 is reached.

7. RECORDS/TEST SHEETS

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

8. ATTACHMENTS

8.1. Example Data Sheet

8.2. Photograph of TSI 8130 CertiTester with chuck open

8.3. Close up of respirator test fixture in the closed chuck 
Procedure No. TEB-APR-STP-0052 Revision: 3.2 Date: 22 October 2019 Page 6 of 8

8.1 Example Data Sheet
Procedure No. TEB-APR-STP-0052 Revision: 3.2 Date: 22 October 2019 Page 7 of 8

8.2 Photograph of TSI 8130 CertiTester with chuck open

8.3 Close up of respirator test fixture in the closed chuck
Procedure No. TEB-APR-STP-0052 Revision: 3.2 Date: 22 October 2019 Page 8 of 8

Revision History

Revision Date Reason for Revision

1.0 20 March 2002 Historic document

1.1 24 August 2005 Update header and format to reflect lab move from Morgantown, WV

No changes to method

2.0 06 August 2007 Significant rewrite of RCT-APR-STP-0051-56. Changes affect form 

and provide clarification of technical content.

2.1 21 August 2012 Removed reference to SMPS, removed product-specific reference for 

Type A/E glass filter, added information on green-line media, 

removed references to 6 work instructions, removed photographs of 

outdated equipment.

3.0 25 March 2014 The requirement for “the final 5 readings to 30 ± 5 mg of loading” 

was rewritten to the “bandwidth of the last 30 ± 5 mg for each filter” 

which matches current laboratory procedures in sections 5.4, 5.4.1, 

and 6.3. Section 5.5 has been modified from 5 data point readings to 

the bandwidth readings over the 30 ± 5 mg on which the “no further 

decrease in efficiency” determination is made or the initial 

unacceptable bandwidth readings. Editorial change made to 6.1.

3.1 12 April 2016 Update to facility address in main title block, the accuracy of the 

timer specified in 3.4.1., is now expressed as percent, and Section 

4.4.1., has been changed to allow for three unused sheets of media to 

be added to the two used sheets in lieu of five new (unused) sheets of 

media. Corrected the P&A statement in section 4.3.

3.2 22 October 2019 With the greatest impact occurring in Section 4, this revision 

represents an update to current content and editorial standards, with 

no change to method or criteria.