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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-0086 Revision: 0.0 Date: 23 March 2020

DETERMINATION OF LOW FLOW WARNING DEVICE ACTIVATION FOR 

BREATH ASSIST TYPE TIGHT-FITTING POWERED AIR-PURIFYING RESPIRATORS

STANDARD TESTING PROCEDURE (STP)

1. PURPOSE

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

flow warning device requirement for breath assist type tight-fitting 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 Breath

Assist Type Tight-Fitting Powered Air-Purifying Respirators 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. The list of necessary test equipment and materials follows:

3.1.1. National Instruments NI USB-9215A Portable USB-Based DAQ with 

Simultaneous Sampling; LabVIEW 2013; test software. 

3.1.2. Mechanical Breather with 622 Kg.m/min. Cam as per U.S. BOM Drawings C1748 (3/17/69) Breathing Machine and B-1198 (3/6/69) Breathing Cam. Or 

equivalent. 

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

equivalent. 

3.1.4. Validyne Engineering model DP45-20 transducer used with Validyne 

Engineering model CD-19A carrier demodulator mounted in the Validyne MC1-

333 module case. Accuracy: ± 0.5% F.S., pressure range up to 3.5 inches of 

water. Or equivalent. 

3.1.5. 3-Liter lung in bottle with plastic tubing, Hans Rudolph Co. part number CM 

1435, or equivalent. 

3.1.6. Electronic Timer calibrated to hundredths of a second. 

4. TESTING REQUIREMENTS AND CONDITIONS
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Procedure No. CVB-APR-STP-0086 Revision: 0.0 Date: 23 March 2020 Page 2 of 6 

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.

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. Follow individual instruction manuals 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. 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.

5.3. Perform pre-test balancing of transducer and recording system.

5.3.1. Connect the transducer to be used during testing to a pressure regulated air 

supply. A pinch clamp, used for slight pressure changes, is placed in-line. An 

alternate method to generate low pressures for calibration is to use the Dwyer 

model A-396A calibration pump or equivalent. 

5.3.2. Connect the transducer cable to the CD-19A demodulator in the MC1-333 

module case, and then connect the demodulator system to the National 

Instruments DAQ. The DAQ is then connected to the PC via USB port. Turn the 

system on and press the Calibration button. After the calibration screen appears, 

with no load applied to the transducer, press the Zero button to set the zeropressure point. 

5.3.3. Apply a pressure of 0.5 inches of water to the transducer system. Check that the 

demodulator display reads 0.5 inches and adjust pressure if necessary. Then 

check that the waveform displayed is at 0.5 inches and adjust the LabVIEW 

readout if necessary.
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Procedure No. CVB-APR-STP-0086 Revision: 0.0 Date: 23 March 2020 Page 3 of 6 

5.3.4. Repeat step 5.1.3 with the pressures of 1.0, 1.5, and 2.0 inches of water until each 

pressure point reads correctly on the waveform. No adjustments should be 

necessary at this point.

5.3.5. Verify that the pressures are correct, by applying pressure at 1.5, 0.5, and 0.0 

inches of water in descending order ensuring each pressure point reads correctly 

on the waveform. If adjustments are necessary, then repeat the calibration 

process for all pressures.

5.3.6. After the calibration sequence is complete, remove the pressure source from the 

system.

5.4. Low flow warning device activation for breath assist type tight-fitting powered air 

purifying respirators. 

5.4.1. Take precautions to mount the pressure transducer in a manner that isolates it 

from shock and vibration, in particular, that which is induced by the breathing 

machine and the operation of the PAPR100.

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

pertinent User’s Instructions. Do not connect headform to breathing machine. 

5.4.3. Turn on breathing machine and use a timer or the built-in tachometer to verify 

that the cam is operating at 24 rpm (24 rpms yields a 40 lpm volume). Stop the 

breathing machine when the pistons are at the end of the upstroke and reset 

counter to zero.

5.4.4. Check that the waveform reads zero, then hit the Data Entry button and enter the 

task number, date, make and model of the unit being tested. (While this is being 

done the transducer should be connected to the recorder, but the transducer 

should not have any pressure load on it). 

5.4.5. Connect the headform with the PAPR100 mounted to the lung-in-bottle 

assembly, using the tubing side that is connected to the breathing bag inside the 

bottle, and then connect the other tube from the lung in bottle to the breathing 

machine. Connect pressure transducer of the PC-based recording system to 

resistance port of the headform with a short length of tubing. Pressure is 

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

5.4.6. Turn on the PAPR100 and the breathing machine. Ensure that no air flow 

warnings are present on the respirator.

5.4.7. Hit the Start button on the PC test software to begin data collection. 

5.4.8. 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.
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Procedure No. CVB-APR-STP-0086 Revision: 0.0 Date: 23 March 2020 Page 4 of 6 

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

device activates. Carefully adjust the flow restriction to determine the point at 

which the minimum restriction activates the low flow warning device. Save the 

pressure tracings for the breaths both immediately before and after warning 

activation.

5.4.10. Turn off the PAPR100 and breathing machine.

5.4.11. Retrieve the tracings for data analysis from the PC –based system which uses a 

custom LabView test software operating code to display the results. 

5.5. Data Analysis

5.5.1. The PC-based system produces a trace showing the inhalation (negative) and 

exhalation (positive) breathing resistance. For this test the inhalation phase for 

the breaths both immediately before and after low flow warning device activation 

is the component for analysis. The PC-based system can be adjusted for sizing, 

i.e. how many peaks will appear on the screen. The spread of the waveform on 

the PC display will not affect the results. 

5.5.2. For a breath assist type tight-fitting PAPR100, a greater than 115 LPM air flow is 

indicated by positive the peak values of the inhalation tracings with respect to the 

base-line (zero) established at the time the system is calibrated. A less than 115 

LPM air flow is indicated by negative peak values of the inhalation tracings with 

respect to the base-line. The PC-based system will automatically log and display 

any negative peaks with sufficient area to qualify as conditions that are less than 

the minimum required air flow. 

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. 

6.1.1.1. For a breath-assist type tight-fitting PAPR100, conditions below the 

minimum allowable flow of 115 LPM are indicated by a negative 

pressure measured inside the facepiece in relation to the immediate 

environment, during both inhalation and exhalation. 

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. 
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Procedure No. CVB-APR-STP-0086 Revision: 0.0 Date: 23 March 2020 Page 5 of 6 

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-0086 Revision: 0.0 Date: 23 March 2020 Page 6 of 6 

Revision History

Revision Date Reason for Revision

0.0 23 March 2020 Original Release