Approvals: 1st Level 2nd Level 3rd Level 

National Institute for Occupational Safety and Health 

National Personal Protective Technology Laboratory 

P.O. Box 18070 

Pittsburgh, PA 15236 

Procedure No. RCT-ASR-STP-0135 Revision: 1.1 Date: 27 September 2005

DETERMINATION OF INHALATION AND EXHALATION BREATHING RESISTANCE, CLOSEDCIRCUIT, DEMAND AND PRESSURE-DEMAND, SELF-CONTAINED BREATHING APPARATUS 

STANDARD TESTING PROCEDURE (STP) 

1. PURPOSE

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

inhalation and exhalation breathing resistance requirements on Closed-Circuit, Demand and 

Pressure-Demand, Self-Contained Breathing Apparatus (SCBA) 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), and 

Subpart H, Section 84.70(a)(1), 84.90(a)(c), and 84.91(e); Volume 60, Number 110, June 8, 1995. 

2. GENERAL

This STP describes the Determination of Inhalation and Exhalation Breathing Resistance, ClosedCircuit, Demand and Pressure-Demand, Self-Contained 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. The list of necessary test equipment and materials follows: 

3.1.1. Two channel thermal tip recording system (Gould Model No. RS3200) with 

carrier amplifier (Model No. 13-4615-35) or equivalent.

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3.1.2. Mechanical Breather with 622 Kg.m/min. Cam as per U.S. BOM Drawings 

C-1748 (3/17/69) Breathing Machine and B-1198 (3/6/69) Breathing Cam or 

equivalent. 

3.1.3. ISI anthropometric test head with tube for measuring breathing resistance 

(International Safety Instruments - Model SR-085) or equivalent. 

3.1.4. Temperature compensated pressure transducer (Validyne Engineering Model No. 

DP45) or equivalent. 

3.1.5. Electric Timer, calibrated to hundredths of a minute (Precision Scientific 

Company) or equivalent. 

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3.1.6. Wet Test - Gas Meter (American Meter Company - Model AL17-1), 1 liter per 

rev. or equivalent. 

3.1.7. Check Valve. 

3.1.8. Flow Control Valve (Gas Valve). 

3.1.9. Haskel Oxygen Pump (6000psig) - Model 17495-AGD-30 or equivalent. 

3.1.10. Dwyer Slant Manometer 0-3", F. W. Dwyer Manufacturing Co., Michigan City, 

Indiana or equivalent. 

4. TESTING REQUIREMENTS AND CONDITIONS

4.1. Prior to beginning any testing, all measuring equipment to be used must have been 

calibrated in accordance with the manufacturer’s calibration procedure and schedule. At 

a minimum, all measuring equipment utilized for this testing must have been calibrated 

within the preceding 12 months using a method traceable to the National Institute of 

Standards and Technology (NIST). 

4.2. The compressed gas cylinder must meet all applicable Department of Transportation 

requirements for cylinder approval as well as for retesting/requalification. 

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4.3. Normal laboratory safety practices must be observed. This includes all safety precautions 

described in the current ALOSH Facility Laboratory Safety Manual. 

4.3.1. Safety glasses, lab coats, and hard-toe shoes must be worn at all times. 

4.3.2. Work benches must be maintained free of clutter and non-essential test 

equipment. 

4.3.3. When handling any glass laboratory equipment, lab technicians and personnel 

must wear special gloves which protect against lacerations or punctures. 

5. PROCEDURE

Note: Reference Section 3 for equipment, model numbers and manufacturers. For calibration 

purposes use those described in the manufacturer's operation and maintenance manuals. 

Test Procedure for Inhalation Breathing Resistance of Closed-Circuit, and Exhalation Breathing 

Resistance of Closed-Circuit and Closed-Circuit Positive Pressure

5.1. Turn on recorder and allow at least 30-minutes warmup. 

PRE-TEST BALANCING OF TRANSDUCER AND RECORDER

5.1.1. Connect the transducer to be used during testing in parallel with a manometer. 

Attach the manometer and transducer to a pressure regulated air. A pinch clamp, 

used for slight pressure changes, is placed inline with two equal lengths of tubing 

for the manometer and transducer connections. 

5.1.2. Connect the transducer cable to the carrier amplifier in the chart. Calibrate the 

recorder and carrier amplifier per instruction manual. Press the 5 mm/sec chart 

speed button. With no load applied to the transducer/manometer system, adjust 

the “POSITION” potentiometer on the chart recorder until the pen is at the midscale position. Press the STOP button on the chart recorder. 

5.1.3. Apply a pressure of 0.5 inches of water to the transducer/manometer system. 

Press the 5 mm/sec chart speed button. Adjust the “CAL” potentiometer on the 

carrier amplifier until the pen on the chart recorder is at the next bold line left of 

mid-scale position. This represents 0.5 inches of water. Press the STOP button 

on the chart recorder. 

5.1.4. Reduce the pressure to 0.0 inches of water to the transducer/manometer system. 

Press the 5 mm/sec chart speed button and check the chart recorder pen is at zero 

mid-scale position. Make any necessary adjustments. Press the STOP button on 

the chart recorder. 

5.1.5. Repeat steps 5.1.3. and 5.1.4. with a pressures of 1.0 , 1.5, and 2.0 inches of 

water until no adjustments are necessary at the “CAL” potentiometer on the 

carrier amplifier. 

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5.1.6. After the calibration sequence is complete remove the pressure source from the 

system. 

5.2. Assemble the apparatus as shown in Figure 1. Mount the pressure transducer where 

shock and vibration are minimal. 

5.3. Fill SCBA cylinder with oxygen to the DOT certified pressure (as stamped on bottle). A 

"+" indicates that the DOT pressure may be exceeded by 10%. 

5.4. Assemble respirator. Mount facepiece on anthropometric head, taking care not to block 

resistance port below and left of nose, particularly if a nosecup is used. Make sure that 

the face seal is leak tight by blocking-off inhalation port of facepiece and inhaling 

through the breathing tube port exiting back of head. After building up several inches of 

negative pressure hold breath several seconds, which will enable you to determine if a 

leak is present. If there is a leak, readjust headstraps and facepiece position and repeat 

leak test until a seal is obtained. 

5.5. Connect regulator or breathing tube to facepiece. Do not connect head to breathing 

machine. Turn on breathing machine and use a timer to determine to determine that the 

cam is operating at 24 rpm. (This will give a 40 lpm volume). Stop breathing machine 

so that it is ready to begin on inhalation stroke. 

5.6. Empty respirator breathing bag completely so that the demand valve will activate when 

the breathing machine is turned on. This will give maximum negative component of 

inhalation phase of breathing cycle. Do not use the first or second breathing cycles for 

inhalation resistance measurement. 

5.7. Zero the recorder base-line to mid point of chart paper. (while this is being done the 

transducer should be connected to the recorder but the transducer should not have any 

load on it). 

5.8. Connect head to breathing machine. Connect transducer to resistance port with a short 

length of tubing. 

5.9. Open cylinder valve full and open main line valve full. Make sure the by-pass valve is 

closed. 

5.10. Record all attenuation and speed settings directly on chart. Turn on breathing machine 

and recorder simultaneously, and operate recorder at change chart speed of 20 mm/sec. 

Cycle respirator from initial emission valve activation until the bag is full and the relief 

valve is operating. This will give the entire range of breathing resistance; i.e., from 

emission valve activation (maximum negative peak to relief valve operation (maximum 

positive peak). This may take several minutes. 

5.11. When tracings are complete - Turn off breathing machine, recorder, and cylinder valve 

on SCBA and bleed down high-pressure air trapped in breathing circuit by removing the 

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tubing from the transducer. 

5.12. Retrieve the tracings on chart paper for data analysis. 

Test Procedure for Inhalation Resistance of Positive Pressure Closed-Circuit

5.13. Follow steps (5.1., 5.2., 5.4., 5.5., 5.7., and 5.8.) from the procedure above. 

5.14. Place a "T" between the Anthropometric Head and Breathing Machine. 

5.15. Connect the open end to: 

a) a one way exhalation check valve 

b) a variable flow control valve 

c) a wet test meter (1-3 LP revolution); sequentially with Tygon tubing. 

5.16. Pressurize the oxygen cylinder to approximately 30 percent of service pressure. 

5.17. Turn on the SCBA oxygen cylinder. 

5.18. Set the exhalation portion flow thru the wet test meter to 2.5 + 0.5 lpm by using the 

variable flow control valve with the breathing machine in operation at a 40 lpm volume at 

24 RPM. 

5.19. Once adjustment is complete, recharge the oxygen cylinder to approximately 30% of 

service pressure and replace in unit. 

5.20. a) turn on SCBA oxygen cylinder (fully open), 

b) turn on recorder (set to desired chart speed), 

c) turn on breathing machine (as calibrated). 

5.22. Cycle breathing machine as required until the admission/demand valve is activated. 

Continue until the admission valve has been activated three times. 

5.23. When tracings are complete - Turn off breathing machine, recorder, and cylinder valve 

on SCBA and bleed down high-pressure air trapped in breathing circuit by removing the 

tubing from the transducer. 

5.24. Retrieve the tracings on chart paper for data analysis. 

5.25. Data Analysis 

5.25.1. The recorder produces a trace showing the inhalation (negative) and exhalation 

(positive) breathing resistance. The inhalation and exhalation phase are the 

components for analysis. With a chart speed of 20 mm/sec., one complete cycle 

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phase (inhale and exhale) should measure approximately 50 mm (See Figure 2.). 

5.25.2. Looking at the tracing will show that the first spike of the inhalation phase is the 

result of the admission valve opening. The final spike in the exhalation phase 

will show the relief valve in operation; i.e., dumping excess oxygen since the 

breathing bag is full (see step 5.1.10. in test procedure). 

5.25.3. The peak values of the inhalation tracing and the exhalation tracing1

 are in 

inches of water column height on the chart tracings. (See Figure 2.) These peak 

values should be examined at the beginning cycle and ending cycle. 

5.25.4. For demand apparatus all exhalation values may not exceed 2.0 inches of water 

column height and the inhalation values may not exceed the difference between 

the exhalation value and 4 inches of water pressure or total swings of 4 inches 

when adding inhale and exhale pressures. Measure inhalation value at point 1, 

ignoring the peak value for demand valve activation. This initial activation is 

only a fraction of the initial inhalation tracing and only occurs periodically during 

hard work and does not significantly contribute to the respiratory workload, 

particularly since demand-type devices are required to deliver at least 30 lpm 

fully open and breathing bag will hold 5-6 liters capacity. Then measure peak 

value at point A. Add values obtained at 1 and A to obtain total pressure swing of 

initial cycle. Do the same for exhalation by measuring and adding peak values at 

points 4 and D ignoring the relief valve pressure spike since this value is 

determined in another test procedure. 

5.25.5 For pressure-demand apparatus all exhalation values may not exceed 2.0 inches 

of water column height and the inhalation values may not drop below ambient 

pressure with and without emission valve in operation2

. Exhalation resistance as 

with demand units is determined at maximum deflection ignoring the relief valve 

pressure spike. 

Note: 1

When reading the inhalation tracing for a positive pressure closed circuit the exhalation 

portion of the breathing curve should be discarded as the test set up will give erroneous 

readings. 

Note: 2

Discard first and second cycles to allow for apparatus system (breathing circuit) to 

equalize. 

Note: This test should be done on a minimum of two respirators, or more if additional testing is 

required (42 CFR, Part 84, Sections 84.12, 84.30, and 84.60). 

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), and Subpart H, Section 84.70(a)(1), 84.90(a)(c), and 84.91(e); Volume 60, 

Number 110, June 8, 1995. 

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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. 

84.70 Self-contained breathing apparatus; description. 

(a) Self-contained breathing apparatus, including all completely assembled, portable, selfcontained devices designed for use as respiratory protection during entry into and escape 

from or escape only from hazardous atmospheres, are described as follows: 

(1) Closed-circuit apparatus. An apparatus of the type in which the exhalation is 

rebreathed by the wearer after the carbon dioxide has been effectively removed and a 

suitable oxygen concentration restored from sources composed of: 

(i) Compressed oxygen; or 

(ii) Chemical oxygen; or 

(iii) Liquid-oxygen. 

84.90 Breathing resistance test; inhalation. 

(a) Resistance to inhalation airflow will be measured in the facepiece or mouthpiece 

while the apparatus is operated by a breathing machine as described in 84.88. 

(c) The inhalation resistance of closed-circuit apparatus shall not exceed the difference 

between exhalation resistance (84.91(e)) and 10 cm. (4 inches) water-column height. 

84.91 Breathing resistance test; exhalation. 

(e) Resistance to exhalation airflow will be measured in the facepiece or mouthpiece of 

closed-circuit apparatus with a breathing machine as described in 84.88, and the 

exhalation resistance shall not exceed 51 mm. (2 inches) water-column height. 

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7. RECORDS\TEST SHEETS

7.1. All test data will be recorded on the BREATHING RESISTANCE - INHALATION 

AND EXHALATION, DEMAND AND PRESSURE-DEMAND, CLOSED-CIRCUIT, 

SELF-CONTAINED BREATHING APPARATUS test data sheet. 

7.2. All videotapes and photographs of the actual test being performed, or of the test 

equipment shall be maintained in the task file as part of the permanent record. 

7.3. All equipment failing any portion of this test will be handled as follows; 

7.3.1. If the failure occurs on a new certification application, or extension of approval 

application, send a test report to the RCT Leader and prepare the hardware for 

return to the manufacturer. 

7.3.2. If the failure occurs on hardware examined under an Off-the-Shelf Audit the 

hardware will be examined by a technician and the RCT Leader for cause. All 

equipment failing any portion of this test may be sent to the manufacturer for 

examination and then returned to NIOSH. However, the hardware tested shall be 

held at the testing laboratory until authorized for release by the RCT Leader, or 

his designee, following the standard operating procedures outlined in Procedure 

for Scheduling, and Processing Post-Certification Product Audits, RB-SOP0005-00. 

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Procedure No. RCT-ASR-STP-0135 Revision: 1.1 Date: 27 September 2005 Page 10 of 16 

BREATHING RESISTANCE - INHALATION AND EXHALATION, DEMAND AND 

PRESSURE-DEMAND, CLOSED-CIRCUIT, SELF-CONTAINED BREATHING APPARATUS

Project No. : Date: __________ 

Company : ________________________________________ 

Respirator Type : ________________________________________ 

Reference: 42 CFR Part 84, Subpart H, Section 84.70(a)(1), 84.90(a)(c), and 84.91(e). 

Requirements: 84.90 - Inhalation Resistance 

(a) Resistance to inhalation airflow will be measured in the facepiece or mouthpiece 

while the apparatus is operated by a breathing machine. 

(c) The inhalation resistance of closed-circuit apparatus shall not exceed the difference 

between exhalation resistance (Section 84.91) and 10 cm (4 inches) water-column height. 

 84.91 - Exhalation Resistance 

(e) Resistance to exhalation airflow will be measured in the facepiece or mouthpiece of 

closed-circuit apparatus with a breathing machine, and the exhalation resistance shall not 

exceed 51`mm (2 inches) water-column height. 

Results: 

 Unit 1 ("H2O) Unit 2 ("H2O)

Exhalation: ___________ 

Inhalation: ___________ 

Comments : 

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________ 

Test Engineer: PASS FAIL________ 

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Figure 1. 

Test Set-up for Measuring Inhalation and Exhalation Breathing Resistance. 

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Figure 2. 

Breathing Resistance Trace. 

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Revision History 

Revision Date Reason for Revision 

1.0 24 May 2001 Historic document 

1.1 27 September 

2005 

Update header and format to reflect lab move from Morgantown, WV 

No changes to method 

 

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