Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

National Institute for Occupational Safety and Health

National Personal Protective Technology Laboratory

626 Cochrans Mill Road 

Pittsburgh, PA 15236

Procedure No. RCT-ASR-STP-0139 Revision: 2.0 Date: 22 April 2019

DETERMINATION OF FACEPIECE CARBON DIOXIDE CONCENTRATION

LEVELS - SELF-CONTAINED BREATHING APPARATUS

STANDARD TESTING PROCEDURE (STP)

1. PURPOSE

This document establishes the standard procedure for ensuring that Self-Contained Breathing

Apparatus (SCBA) submitted for Approval, Extension of Approval, or examined during Certified

Product Audits, meet the minimum certification standards for carbon dioxide concentration as

allowed for at 42 CFR, Part 84, Subpart G, Section 84.63(a)(c)(d), and Subpart H, Section

84.97(a)(b)(c); Volume 60, Number 110, June 8, 1995.

2. GENERAL

This STP describes the Determination of Facepiece Carbon Dioxide Concentration Levels - SelfContained Breathing Apparatus test 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/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)

3.3. Instrument-grade carbon dioxide (CO2) 

3.4. Instrument-grade air

3.5. Two-stage regulator with control valve for CO2 cylinder (first stage gauge with 3000 psig 

capacity; second stage gauge with 0 - 100 psig capacity) 

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

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

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

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

3.10. AEI Technologies Model N-22M O2 gas sensor or equivalent
Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Procedure No. RCT-ASR-STP-0139 Revision: 2.0 Date: 22 April 2019 Page 2 of 11

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

or equivalent

3.12. 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 

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

a Carbon Dioxide flow control range of 0 to 1000 sccm

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

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

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

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

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

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

inches H2O column measurement range, or equivalent

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

inches linear displacement

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

3.20. Multiple outlet box with 6 receptacles

3.21. Two adjustable jack stands

4. TESTING REQUIREMENTS AND CONDITIONS

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 

measurement equipment utilized for this testing shall have been calibrated using a method 

traceable to recognized international standards when available. Except where specifically 

instructed, refer to the manufacturers’ operation and maintenance manuals for operation and 

calibration instructions.

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.
Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Procedure No. RCT-ASR-STP-0139 Revision: 2.0 Date: 22 April 2019 Page 3 of 11

5.1.2. Adjust the zero potentiometer to 0.04% for the CO2 gas analyzer and 20.95% 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 

20.95%, 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).

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 Attachment 8.1. The 

CO2 pickup, O2 pickup, and pressure transducer shall be mounted where shock 
Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Procedure No. RCT-ASR-STP-0139 Revision: 2.0 Date: 22 April 2019 Page 4 of 11

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 of tubing has an 

internal 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 headform mouth 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. For open-circuit apparatus, 

connect the entire apparatus to the facepiece, place the regulator in the desired 

mode of operation, and open the compressed-air cylinder valve on SCBA. On the 

closed-circuit apparatus, only those parts contributing to dead air space are 

tested. Exhaled CO2 must be released and not permitted to re-enter the closedcircuit apparatus during inhalation. Record the CO2 concentration at the mouth of 

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

respiratory cycles (see Attachment 8.2.) using the data monitoring/recording 

software application. Analysis of the recorded test parameters provides the 

average CO2 concentration contributed by the apparatus and/or facepiece being 

tested.

5.3.8. Disconnect the entire apparatus from the facepiece, if applicable. Remove the 

facepiece from the headform. Repeat the actions outlined in Section 5.3.7 two 

additional times, for a total of three dons. 
Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Procedure No. RCT-ASR-STP-0139 Revision: 2.0 Date: 22 April 2019 Page 5 of 11

5.4. Data is to be analyzed as follows:

5.4.1. 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 Attachment 

8.2. 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 back in time 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 Attachment 8.2.) 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 Attachment 8.2.). 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 = (Σ CO2 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:

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. 
Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Procedure No. RCT-ASR-STP-0139 Revision: 2.0 Date: 22 April 2019 Page 6 of 11

Avg. Blank CO2 = (Σ CO2 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 according to 42 CFR, Part 84, Subpart G, 

Section 84.63(a)(c)(d), and Subpart H, Section 84.97(a)(b)(c); 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.

84.97 Test for carbon dioxide in inspired gas; open- and closed-circuit apparatus; 

maximum allowable limits – 

(a) Open-circuit apparatus:

(1) The concentration of carbon dioxide in inspired gas in open-circuit apparatus will be 

measured at the mouth while the apparatus mounted on a dummy head is operated by a 

breathing machine. An acceptable method for measuring the concentration of carbon 

dioxide is described in Bureau of Mines Report of Investigations 6865, A Machine-Test 

Method for Measuring Carbon Dioxide in the Inspired Air of Self-Contained Breathing 

Apparatus, 1966. Copies of Report of Investigations 6865 may be inspected or obtained 
Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Procedure No. RCT-ASR-STP-0139 Revision: 2.0 Date: 22 April 2019 Page 7 of 11

from the NIOSH, Technology Evaluation Branch, 626 Cochrans Mill Road, Pittsburgh, 

Pennsylvania 15236. 

(2) The breathing rate will be 14.5 respirations per minute with a minute-volume of 10.5 

liters.

(3) A sedentary breathing machine cam will be used.

(4) The apparatus will be tested at a temperature of 27° ±2°C. (80° ±5°F).

(5) A concentration of 5 percent carbon dioxide in air will be exhaled into the facepiece. 

(b) Closed-circuit apparatus. The concentration of carbon dioxide in inspired gas in 

closed-circuit apparatus will be measured at the mouth while the parts of the apparatus 

contributing to dead-air space are mounted on a dummy head and operated by the 

breathing machine as in paragraphs (a)(1) through (5) of this section. 

(c) During the testing required by paragraphs (a) and (b) of this section, the concentration 

of carbon dioxide in inspired gas at the mouth will be continuously recorded, and the 

maximum average concentration during the inhalation portion of the breathing cycle shall 

not exceed the following limits.

Maximum Average Concentration of Carbon Dioxide in Inspired Air

Where the service time is - CO2 percent by volume 

Not more than 30 minutes...... 2.5 

1 hour....................... 2.0 

2 hours...................... 1.5 

3 hours...................... 1.0 

4 hours...................... 1.0 

7. RECORDS/TEST SHEETS

7.1. Record test data in a format that shall be stored and retrievable. Data to be recorded and 

reported as shown in the attached data sheet (Attachment 8.3.).

8. ATTACHMENTS

8.1. NIOSH CO2 Deadspace Test System Schematic with Description of Components

8.2. NIOSH CO2 Deadspace Test Data Plot

8.3. Facepiece Carbon Dioxide of Self-Contained Breathing Apparatus Test Data Sheet
Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Procedure No. RCT-ASR-STP-0139 Revision: 2.0 Date: 22 April 2019 Page 8 of 11

Attachment 8.1. 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
Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Procedure No. RCT-ASR-STP-0139 Revision: 2.0 Date: 22 April 2019 Page 9 of 11

Attachment 8.2. NIOSH CO2 Deadspace Test Data Plot
Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Procedure No. RCT-ASR-STP-0139 Revision: 2.0 Date: 22 April 2019 Page 10 of 11

Attachment 8.3. Facepiece Carbon Dioxide of Self-Contained Breathing Apparatus Test Data Sheet 
Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Procedure No. RCT-ASR-STP-0139 Revision: 2.0 Date: 22 April 2019 Page 11 of 11

Revision History

Revision Date Reason for Revision

1.0 15 February 2001 Historic document

1.1 21 September 2005 Update header and format to reflect lab move from Morgantown, 

WV

No changes to method 

2.0 22 April 2019 Edited to current style and format. The underlying procedure is 

largely unchanged, but the data analysis method is updated to rely 

upon a digital transformation of the transducer signals rather than 

graphic analysis of a strip chart. Changes to the list of equipment,

Section 3, and changes to the procedure, Section 5, support the

updated method of analyzing the data.