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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. RCT-APR-STP-0064 Revision: 1.2 Date: 24 July 2020

DETERMINATION OF FACEPIECE CARBON-DIOXIDE AND OXYGEN CONCENTRATION 

LEVELS OF TIGHT FITTING, POWERED AIR-PURIFYING RESPIRATORS, 

WITH THE BLOWER UNIT OFF OR NON-POWERED RESPIRATORS

STANDARD TESTING PROCEDURE (STP)

1. PURPOSE

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

the facepiece against carbon-dioxide build up and maintaining the oxygen concentration 

level requirements on tight fitting, powered air-purifying respirators (PAPR), with the 

blower unit off, or non-powered respirators, with a neck seal designed to offer personal 

protection against particulate and gas/vapor hazards, including CBRN Air Purifying 

Escape Respirators (APER), submitted for Approval, Extension of Approval, or 

examined during Certified Product Audits, meet the minimum certification standards set 

forth in 42 CFR, Part 84, Subpart G, Section 84.63(a)(c)(d); Volume 60, Number 110, 

June 8, 1995.

1.2. While wearing this type of device, the user exhales approximately 5% carbon dioxide 

into the facepiece. Most of this CO2 exits through an exhalation valve to the external 

environment. The residual exhaled portion that remains in the facepiece and is 

rebreathed during inhalation is the portion of prime concern and is the object of the test 

requirement and this test procedure. A small amount of CO2 is physiologically required in 

order to stimulate respiration; but once concentration levels increase beyond 

approximately 2% CO2, there is a sharp rise in a person's respiratory minute-volume and 

breathing rate. Based on the maximum allowable average CO2 concentration level for 

SCBA as acceptable under CE standards - the maximum acceptable CO2 concentration 

level for a PAPR with the blower off and non-powered gas masks with a tight fitting neck 

seal, including CBRN APERs, used for escape purposes will be 2%.

2. GENERAL

2.1. This procedure describes the Determination of Facepiece Carbon-Dioxide and Oxygen 

Concentration Levels of Tight Fitting, Powered Air-Purifying Respirators, With the 

Blower Unit Off or Non-Powered Respirators test in sufficient detail that a person in the 

appropriate technical field can conduct the test and determine whether or not the product 

passes testing.

3. EQUIPMENT/MATERIALS

3.1. Scott Aviation mechanical breather with sedentary cam and solenoid valves attached. 

3.2. Thin-walled flexible plastic reservoir with a low resistance relief valve (less than 1-inch 

water column).
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3.3. Instrument grade CO2. 

3.4. Instrument grade air.

3.5. Specialty calibration gas mixture containing 5.00% CO2 with the balance air.

3.6. AEI Technologies CD-3A CO2 gas analyzer, 0 – 15%, or equivalent

3.7. AEI Technologies Model P-61B CO2 gas sensor, or equivalent

3.8. AEI Technologies S-3A/I Oxygen (O2) gas analyzer, 0 – 100%, or equivalent

3.9. AEI Technologies Model N-22M O2 gas sensor or equivalent 

3.10. AEI Technologies Model R-1 Flow Control unit or vacuum pump for gas sample system, 

or equivalent 

3.11. MKS Instruments Model No. 1179A618CS1BV Mass Flow Controller (MFC) for gas 

sample system flow control with a 5% CO2/95% air mixture flow control range of 0 to 

715 sccm, or equivalent

3.12. MKS Instruments Mass Flow Controller Model No. 1179A13CS1BV, or equivalent, with 

a Carbon Dioxide flow control range of 0 to 1000 sccm

3.13. MKS Instruments Mass Flow Controller Model No. 1179A24CS1BV-S, or equivalent, 

with an air flow control range of 0 to 15,000 sccm

3.14. MKS Instruments Type 247 4-Channel Power Supply Readout, or equivalent

3.15. Validyne Engineering Corporation Single-Channel Digital Transducer Indicator/Power 

Supply, Model No. CD-23-A-2-A-1-C, or equivalent 

3.16. Validyne Engineering Corporation DP45-16 4516A3S4D Pressure Transducer, +/- 1.4 

inches H2O column measurement range, or equivalent

3.17. Acuity AR700-4 Laser Distance Gauge, Part No. AP7010040 or equivalent, 0 – 3.5 

inches linear displacement

3.18. Lee LIF Series 2-Way micro-solenoid control valve, part no. LFAA1206018H 

4. TESTING REQIREMENTS 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. 
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5. PROCEDURE

5.1. Calibration of the AEI Technologies CD-3A CO2 and S-3A/I O2 gas analyzers will be 

performed as follows:

5.1.1. Turn on gas sample system vacuum pump. Set the gas sample system flow rate 

to 450 sccm as controlled by this system’s mass flow controller. 

5.1.2. Adjust the zero potentiometer to 0.04% for the CO2 gas analyzer and 20.93% for 

the O2 gas analyzer, as necessary. 

5.1.3. Administer span gas to the gas sample tube sample point via a tube that is at least 

three times the diameter of the gas sample tube. Use a span gas flow of at least 

500 sccm. The excess span gas will flow around the inlet to the sampling point to 

the atmosphere in the test lab. The gas sample tube sampling point shall be 

inserted at least several inches into the span gas delivery tube and remain in that 

position throughout the CO2 gas analyzer span check and adjustment. 

5.1.4. Adjust the CO2 gas analyzer span potentiometer to the span gas concentration 

(normally 5.00%), as necessary. 

5.1.5. Remove the span gas delivery tube to allow the CO2 and O2 gas analyzers’

outputs to decrease to and stabilize near the zero gas concentrations of 0.04% and 

20.93%, respectively. 

5.1.6. Adequate ventilation must be present in the test area to prevent the build-up of 

CO2 gas near the gas sampling point. 

5.1.7. Repeat steps 5.1.2 through 5.1.5 until the zero and span gas concentrations for 

the CO2 gas analyzer and the zero concentration for the O2 gas analyzer are 

reproducible without further adjustments being necessary. 

5.2. Determination of the CO2 gas analyzer/gas sample system response time will be 

performed as follows:

5.2.1. Administer calibration gas to the gas sample tubing sampling point as controlled 

by the gas sample system delay solenoid valve.

5.2.1.1. Operate the data recording system while activating and deactivating the 

gas sample system delay solenoid valve to detect the times at which the 

calibration gas flow is started/stopped. 

5.2.1.2. The time required to reach 90% of the CO2 gas analyzer span gas 

concentration after activation of the gas sample system delay solenoid 

valve is the CO2 gas analyzer/gas sample system response time (gas 

sample transit time plus gas CO2 gas analyzer response time). 
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5.2.1.3. The gas sample system response time that is determined will be used 

when performing test data analysis.

5.3. CO2 and O2 concentration levels in the facepiece will be determined for the largest size of 

a multiple size device or for a single-size device as follows:

5.3.1. Assemble the CO2 Deadspace Test apparatus as shown in Fig. 1. The CO2

pickup, O2 pickup, and pressure transducer shall be mounted where shock and 

vibration are minimal. Use exactly 20 inches of 3/4 inch I.D. tubing between the 

headform mouth and the breathing machine "T" (this length is critical since the 

response time must correlate closely with the pressure measurement for a 

simultaneous readout). This length of tubing has a volume of approximately 145 

cm3

. 

5.3.2. All test instruments, including the CO2 and O2 gas analyzers, pressure transducer, 

and mass flow controllers should remain powered at all times. If this is not the 

case, allow at least 18 hours for these instruments to reach steady state after they 

are powered before starting testing.

5.3.3. Set the air flow rate to 10.45 liters/min and the CO2 flow rate to 550 cm3

/min

using these streams’ respective mass flow controllers. These flow rates will 

provide a 5% CO2 air mixture at the dummy head during exhalation. The flexible 

bag will be kept filled with slightly more than 10.5 liters/min flow (11.0 

liters/min) and minimize back pressure in the system. To maintain a 5% CO2

concentration in the exhaled breathing gas, some slight readjustment of air and 

CO2 flow rates may be necessary.

5.3.4. Turn on the breathing machine and let it warm-up for one minute. Set the 

potentiometer for 14.5 rpm on the sedentary cam. This will give a flow rate of 

10.5 lpm. 

5.3.5. A LabVIEW-based software application (or equivalent) shall be used to monitor 

all test parameters during testing and to record all test data needed to assess the 

inspired CO2 levels of the respirator being tested.

5.3.6. Run a blank test, operating the equipment to produce the correct CO2 pattern at 

the dummy head mouth. Record the CO2 concentration at the mouth of the 

headform and all other required test parameters for at least three complete 

respiratory cycles using the data monitoring/recording software application. 

Analysis of the recorded test parameters provides the average CO2 concentration 

contributed by the headform. This is a blank value which must be subtracted 

from the total inspired CO2 of all facepiece and breathing apparatus tested. 

5.3.7. Mount the facepiece to be tested on the headform. Record the CO2 concentration 

at the mouth of the headform and all other required test parameters for at least 

three complete respiratory cycles (see Figure 2) using the data 

monitoring/recording software application. Analysis of the recorded test 
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Procedure No. RCT-APR-STP-0064 Revision: 1.2 Date: 24 July 2020 Page 5 of 11

parameters provides the average CO2 concentration contributed by the facepiece 

being tested.

5.3.8. Remove the facepiece from the headform. Repeat the actions outlined in Section 

5.3.7 two additional times, for a total of three dons. 

5.4. Data is to be analyzed as follows:

5.4.1. The test data is recorded at 40 Hz (every 0.025 second) by the LabVIEW 

software application and includes CO2 and O2 volume % measured at the 

headform mouth, facepiece resistance, and linear piston displacement. This data 

is downloaded into an Excel spreadsheet and plots with the three traces shown in 

Fig. 2 are simultaneously produced. 

5.4.2. Prior to analyzing the test data and determining test results, the CO2 and O2

volume % data must be shifted forward by the time equivalent to the gas sample 

system response time. This is necessary to synchronize the CO2 and O2 volume 

% data with the facepiece resistance and linear piston displacement data.

5.4.3. The start of the inhalation phase of a breathing cycle is determined as the point in 

time at which the facepiece resistance (green trace in Fig. 2) begins to drop 

rapidly after the piston resting phase that follows the forward piston stroke. 

5.4.4. The start of the inhalation phase is corroborated by the piston displacement (red 

trace in Fig. 2). The beginning of the inhalation phase is signified as the time at 

which the piston begins to retract (increase in displacement) after the preceding 

piston resting phase. The end of the inhalation phase is signified by the start of 

the piston resting phase that precedes the forward piston stroke. 

5.4.5. The duration of the inhalation phase must correspond to the time between the 

start and end of piston retraction. With a breathing rate of 14.5 breaths per 

minute, the inhalation phase is 1.70 seconds. 

5.4.6. The inspired CO2 level for a facepiece mounted on the headform is determined 

from the recorded test data as follows:

Sum the measured CO2 volume % measurements at 0.025-second increments 

during the inhalation phase and divide by the number of CO2 volume % data 

points (n) measured. Based on the 1.70-second inhalation phase duration, n = 68. 

Avg. Inspired CO2 for facepiece = (ΣCO2 volume %)/n

5.4.7. The inhalation phase for a blank CO2 level determination starts at the last peak

CO2 volume % just prior to the rapid decrease in the CO2 volume %. 

5.4.8. The blank CO2 level is determined from the recorded test data as follows:
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Sum the measured CO2 volume % measurements at 0.025-second increments 

during the inhalation phase and divide by the number of CO2 volume % data 

points (n) measured.

Avg. Blank CO2 = (ΣCO2 volume %)/n

5.4.9. The inspired CO2 level for each don of the respirator being tested is the 

difference between the inspired CO2 for the facepiece and the blank CO2 level 

that was measured.

Inspired CO2 = Avg. Inspired CO2 (facepiece) – Avg. Blank CO2

5.4.10. The reported inspired CO2 level for each respirator is the minimum measured 

inspired CO2 concentration level of the three dons. The reported O2 level for 

each respirator is the minimum O2 level measured during the inhalation phase 

(the period over which the inspired CO2 level is assessed) of the chosen don. 

6. PASS/FAIL CRITERIA

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

84.63(a)(c)(d); Volume 60, Number 110, June 8, 1995. 

6.2. This test establishes the standard procedure for ensuring that: 

 84.63. Test requirements; general.

(a) Each respirator and respirator component shall when tested by the applicant and by 

the Institute, meet the applicable requirements set forth in subparts H through L of this 

part.

(c) In addition to the minimum requirements set forth in subparts H through L of this 

part, the Institute reserves the right to require, as a further condition of approval, any 

additional requirements deemed necessary to establish the quality, effectiveness, and 

safety of any respirator used as protection against hazardous atmospheres.

(d) Where it is determined after receipt of an application that additional requirements will 

be required for approval, the Institute will notify the applicant in writing of these 

additional requirements, and necessary examinations, inspections, or tests, stating 

generally the reasons for such requirements, examinations, inspections, or tests.

6.3. The maximum allowable average carbon dioxide concentration for each sample tested 

shall not exceed 2.0% and the measured oxygen levels at the end of inspiration shall not 

fall below 19.5% (during the same measurement periods for carbon dioxide assessment)

with the respirator operating with the blower off for escape purposes (including CBRN 

PAPRs) or non-powered respirator and CBRN APERs. 

7. RECORDS/TEST SHEETS
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7.1 Record test data in a format that shall be stored and retrievable. Data to be reported as 

shown in attached data sheet. 
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1

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Figure 1. NIOSH CO2 Deadspace Test System Schematic

Key

1 Breathing machine

2 Sedentary cam

3 Headform

4 Airway opening/sampling point

5 Rigid mixing vessel

6 Flexible reservoir

7 Non-return valve

8 Solenoid valve

9 CO2 supply

10 Air supply

11 Calibration gas supply

12 CO2 analyzer

13 O2 analyzer

14 Mass flow controller

15 Pressure transducer

16 Linear displacement transducer

17 Computer
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Figure 2. NIOSH CO2 Deadspace Test Data Plot 
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Procedure No. RCT-APR-STP-0064 Revision: 1.2 Date: 24 July 2020 Page 10 of 11

Table 1. Facepiece Carbon Dioxide or Oxygen Concentration Levels of Tight-Fitting Powered AirPurifying Respirators with the Blower Unit Off or Tight-Fitting Non-Powered Gas Masks with a TightFitting Seal Test Data Sheet
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Revision History

Revision Date Reason for Revision

1.0 10 December 2001 Historic document

1.1 12 September 2005 Update header and format to reflect lab move from Morgantown, WV

No changes to method

1.2 24 July 2020 General update to include LabVIEW-based data monitoring, data 

recording and data analysis methods