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-0132 Revision: 1.1 Date: 20 September 2005

DETERMINATION OF INHALATION BREATHING RESISTANCE - OPEN-CIRCUIT, 

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 breathing resistance requirements on Open-Circuit, 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 84.90(a)(b); Volume 60, Number 110, June 8, 

1995. 

2. GENERAL

This STP describes the Determination of Inhalation Breathing Resistance - Open-Circuit, 

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 C1748 (3/17/69) Breathing Machine and B-1198 (3/6/69) Breathing Cam. 

3.1.3. ISI Anthropometric Test heads with tube for measuring breathing resistance and 

air flows - 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. 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. 

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. 

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

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 

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Procedure No. RCT-ASR-STP-0132 Revision: 1.1 Date: 20 September 2005 Page 4 of 13 

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. 

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 air to pressure as noted in the instruction manual. Make sure the 

pressure is within the DOT certified pressure range. 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). 

5.6. 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). 

5.7. Connect the anthropocentric head with the facepiece to the breathing machine. Connect 

transducer to resistance port with a short length of tubing. Open cylinder valve full and 

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Procedure No. RCT-ASR-STP-0132 Revision: 1.1 Date: 20 September 2005 Page 5 of 13 

open main line valve full. Make sure the by-pass valve is closed. 

5.8. Record all attenuation and speed settings directly on chart paper. Turn on breathing 

machine and recorder simultaneously, and let operate at 1 mm/sec for the duration of the 

breathing cycles (service time). Take at least three separate tracings of several of the 

cycles at 20 mm/sec during the duration of the breathing cycles. (1-cycle includes the 

inhalation and exhalation breathing phases). 

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

on SCBA and then bleed down high-pressure air trapped in breathing hose by opening the 

by-pass valve, then shut the by-pass off. 

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

5.11. Data Analysis 

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

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

component for analysis. With a chart speed of 20 mm/sec., the inhalation phase 

should measure approximately 50 mm. 

5.11.2. The peak inhalation values for a demand open-circuit unit should measure less 

than 1.25" H2O below the baseline established at the time the recorder was 

calibrated. 

5.11.3. For a pressure-demand unit the peak valves of the inhalation tracings shall 

remain positive with respect to the base-line (zero) established at the time the 

recorder is calibrated. (See Figure 2.) At a speed of 20 mm/sec, a negative spike 

is allowed as long as there is no area between the point where the spike goes 

negative and the point where it returns to positive. 

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 84.90(a)(b), 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. 

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Procedure No. RCT-ASR-STP-0132 Revision: 1.1 Date: 20 September 2005 Page 6 of 13 

(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. 

84.90 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. 

(b) The inhalation resistance of open-circuit apparatus shall not exceed 32 mm. (1.25 

inch) water-column height (at a flow rate of 120 liters per minute). 

7. RECORDS\TEST SHEETS

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

INHALATION, OPEN-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-0132 Revision: 1.1 Date: 20 September 2005 Page 7 of 13 

BREATHING RESISTANCE TEST - INHALATION, OPEN-CIRCUIT, 

SELF-CONTAINED BREATHING APPARATUS

Project No.: Date: __________ 

Company : __________________________________________________ 

Respirator Type: ______________________________________________ 

Reference: 42 CFR, Part 84, Subpart H, 84.90(a)(b) - Inhalation Resistance. 

Requirements: 84.90(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. 

84.90(b) The inhalation resistance of a demand open-circuit apparatus shall not exceed 32 

mm. (1.25 inch) water-column height (at a flow rate of 120 liters per minute). 

Results: 

 Unit 1 "H2O Unit 2 "H2O

 Inhalation: __________ 

Comments: 

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________ 

 

 

 

 

Test Engineer: Pass Fail_________ 

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 Test Set-up for Measuring Inhalation Breathing Resistance. Uncontrolled Copy 

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Revision History 

Revision Date Reason for Revision 

1.0 23 May 2001 Historic document 

1.1 20 September 

2005 

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

No changes to method 

 

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