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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. CVB-APR-STP-0088 Revision: 0.0 Date: 23 March 2020

DETERMINATION OF LOW FLOW WARNING DEVICE 

ACTIVATION FOR POWERED AIR-PURIFYING RESPIRATORS, SERIES PAPR100,

STANDARD TESTING PROCEDURE (STP)

1. PURPOSE

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

low flow warning device requirement for powered air-purifying respirators, series PAPR100,

meet the requirements set forth in 42 CFR Part 84, Subpart K, 84.171(j).

2. GENERAL

This procedure describes the Determination of Low Flow Warning Device Activation for

Powered Air-Purifying Respirators, Series PAPR100, test procedure 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. Air-tight chamber – approximately 24 inches by 24 inches by 16 inches with a bolt on 

door, a 3-inch diameter inlet for accepting breathing tubes and adapter, a 1 inch diameter 

outlet, and a 1⁄4 inch outlet for a manometer probe. 

3.2. Setra Datum 2000 Model 239 digital manometer with an accuracy of ± 0.023 in-H2O or 

better, or equivalent.

3.3. Teledyne Hastings L-25S Laminar Mass Flow Meter, or equivalent. 

3.4. Spencer 075-1/3 Centrifugal Blower vacuum source, or equivalent. 

3.5. Anthropometric Headform, in accordance with ISO 16900, size medium, or equivalent.

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. Testing shall be conducted on as-received respirators at 25 ± 2.5 degrees Celsius (°C) and 

adhere to User’s Instructions.
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Procedure No. CVB-APR-STP-0088 Revision: 0.0 Date: 23 March 2020 Page 2 of 4 

4.3. Three complete respirator systems will be evaluated for low flow warning device 

activation.

4.4. Determination of Low Flow Warning Device Visibility will be completed for any 

respirator with a visual warning device. The standard testing procedure is described in 

CVB-APR-STP-0087. 

4.5. Determination of Low Flow Warning Device Sound Level on Series PAPR100 will be 

completed for any respirator with an audible warning device, where the warning provided 

is audible only, or other warnings are not readily apparent. The standard testing 

procedure is described in CVB-APR-STP-0085. 

5. PROCEDURE

5.1. Prior to any testing, the respirator shall be evaluated per the user check instructions in the 

User’s Manual to ensure that the low flow warning(s) activate as designed.

5.2. Test setup for low flow warning device activation for continuous flow powered airpurifying respirators 

5.2.1. The test chamber outlet is connected to the mass flow meter inlet. The mass flow 

meter outlet is connected to the vacuum blower inlet. A flow control valve is 

placed between the mass flow meter and vacuum blower. The vacuum blower 

vents to atmosphere. Ensure that all pipe lengths are sufficient to maintain 

laminar flow.

5.2.2. Mount the respirator to the headform in the as-worn configuration following all 

pertinent User’s Instructions. 

5.2.3. Connect the headform and respirator to the chamber. 

5.2.3.1. On units with breathing tubes, the breathing tube is placed through the 

chamber inlet port and the blower is placed outside of the chamber. The 

headform and respirator are placed inside the chamber. Seal the chamber 

inlet around the breathing tube. 

5.2.3.2. On units without breathing tubes, the headform trachea outlet tube is 

placed through the chamber inlet port and the headform and respirator 

are placed outside the chamber. Seal the chamber inlet around the 

headform outlet tube.

5.2.3.2.1. Loose fitting respiratory inlet coverings may be adjusted to 

capture air-flow that would otherwise exit the respirator.

5.2.4. Connect the digital manometer to the pressure tap on the headform. Pressure is 

measured at a pitot ring positioned 25 mm inside of the trachea inlet.

5.2.4.1. Ensure the manometer has a reading of zero at ambient conditions, and 

adjust if necessary.
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Procedure No. CVB-APR-STP-0088 Revision: 0.0 Date: 23 March 2020 Page 3 of 4 

5.2.5. Close the chamber door and ensure the chamber is sealed.

5.2.6. Turn on the PAPR and the vacuum blower. Ensure that no air flow warnings are 

present on the respirator.

5.2.7. Adjust the flow control valve until manometer has a reading of zero. 

5.2.8. Restrict the flow to the respirator. This is done by incrementally adding 

restriction to the inlet of the respirator, such as attaching small pieces of adhesive 

tape or a similar flow restricting item.

5.2.8.1. While restricting flow to the respirator, adjust the flow control valve to 

ensure that the manometer continuously reads zero.

5.2.9. Add increased flow restriction to the respirator inlet until the low flow warning 

device activates. Record the maximum airflow which activates the low flow 

warning device. 

5.2.10. Turn off the PAPR100 and vacuum blower.

6. PASS/FAIL CRITERIA

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

81.171(j). 

6.1.1. The low flow warning must actively and readily indicate when flow inside the 

respiratory inlet covering falls below the minimum required air flow. The 

minimum air flow shall be 115 LPM for tight-fitting PAPR100 and 170 LPM for 

loose-fitting PAPR100. 

6.1.2. Any warning must be detectable by the wearer without any intervention by the 

wearer.

6.1.3. Warning devices must be configured so that they may not be de-energized while

the blower is energized. 

6.1.4. Any warnings which require different reactions by the wearer must be 

distinguishable from one another. 

7. RECORDS/TEST SHEETS

7.1. Record the test data in a format that shall be stored and retrievable.
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Procedure No. CVB-APR-STP-0088 Revision: 0.0 Date: 23 March 2020 Page 4 of 4 

Revision History

Revision Date Reason for Revision

0.0 23 March 2020 Original Release