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-0138 Revision: 1.1 Date: 26 September 2005

DETERMINATION OF SAFETY RELIEF VALVE OPERATION - CLOSED-CIRCUIT, 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 relief 

valve 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 84.84(i)(1)(2)(3); Volume 60, Number 110, 

June 8, 1995. 

2. GENERAL

This STP describes the Determination of Safety Relief Valve Operation - Closed-Circuit, 

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.

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 2 of 14 

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

air flows - Model SR-085 or equivalent. 

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

DP45) or equivalent. 

3.1.4. Air pump of most any type (low flow capability) or house air source. 

3.1.5. Haskel Oxygen Pump (6000psig) - Model 17495-AGD-30 used for pumping high 

pressure oxygen or equivalent. 

4. TESTING REQUIREMENTS AND CONDITIONS

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

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 3 of 14 

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 during all testing. 

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 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 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 4 of 14 

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 oxygen to the 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 five 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 for all compressed oxygen 

systems which have a constant flow orifice. For all others including liquid air or oxygen, 

solid chemical oxygen generators (KO2, chlorate candles), demand only regulators et al., 

a positive flow pump is connected with a "T" between the transducer and anthropometric 

head. 

5.8. Empty breathing bag completely by compressing bag by hand which dumps all bag 

volume through relief valve. 

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

machine and recorder simultaneously, and let operate at 5 mm/sec. and set attenuator to a 

low value which may have to be increased as bag inflates. Chart speed and attenuator 

settings may have to be changed to cover pressure range and to accentuate or null 

sensitivity desired for tracing since each unit's relief valve has response characteristics 

different from other unit's relief valve. 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 5 of 14 

5.10. Turn on unit (oxygen cylinder) to activate the respirator constant dosage flow to 

approximately 1.5 lpm and allow several minutes for the bag to fill (approximately 5 - 6 

liters) and the relief valve to open fully, which process can be determined by observing 

the pressure tracing on the recorder paper. If the respirator does not have a constant 

flow/dosage capability then turn on the pump placed in line and adjust for a low flow (i.e. 

less than 2 lpm) which can be monitored with a low capacity flow meter in line. If the 

pump has too high a flow rate capacity, it may be necessary to place a "T" in line between 

the pump tubing connection and the "T" in line between transducer and dummy head. 

The open end of the "T" will dump excess flow overboard and a piece of Tygon tubing 

with screw clamp may be installed to gain fine control of flow rate. 

5.11. A series of five or more tracings should be obtained for analysis since spring loaded 

valves tend to take set. Such cycling will relax valve and results of additional tracings 

will be reproducible within a narrow range. 

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

(or pump if used) and bleed down high pressure oxygen trapped in breathing hose and/or 

regulator lines by opening by-pass valve, shut by-pass off. 

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

5.14. Data Analysis 

5.14.1. The recorder produces a trace showing the bag pressure increase with time and 

flow. 

5.14.2. The tracing will be different from respirator to respirator since bag/ relief valve 

characteristics are specific to unit design and operations. Generally most tracings 

fall into two curve types (see Figure 2). 

a. Trace A shows a curve type in which the bag fills and bag folds pop out at points 

such as B, C and D. In order to obtain the bag full point a small ruler should be 

laid on the trace at point E where the relief valve is opening and follow the final 

slope until departure from that slope occurs. This point F is where the bag is 

considered full. Point G is the point at which the relief valve is fully open. The 

segment E to G is not used in final slope determination since the relief valve is 

opening gradually giving a rounded segment. 

b. Trace B shows a curve type in which the bag full point and relief valve open 

point as well as slope rise points are relatively sharply defined. The bag is filling 

at points A to B. This point is determined by laying a ruler on the slope and 

determining the departure location from this slope. This point B is where the bag 

is full, while line D is the relief valve fully open point. Segments B-B1 and C-C1 

are not used in slope determination since they are rounded segments and not 

specifically definable with reference to actual slope. 

5.14.3. The first and second tracing may be eliminated if cycling indicates need for 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 6 of 14 

reproducibility. 

5.14.4. All values may not exceed 69 mm for relief valve fully open operation and the 

difference between the bag full point and relief valve fully open level must be 13 

mm for acceptance. 

5.14.5. The range allowed after a test tolerance is 0.28" H2 O to 0.75"H2 O. All values 

must fall within this range. 

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 84.84(i)(1)(2)(3); 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 

84.84 Hand-operated valves; minimum requirements. 

(i) Safety relief valves or systems, designed and constructed to release excess pressure in 

the breathing circuit, shall be provided on closed-circuit apparatus, and shall meet the 

following requirements: 

(1) The relief valve or system shall operate automatically when the pressure in the 

breathing circuit on the inhalation side of the breathing bag reaches 13 mm. (one-half 

inch) water-column height of pressure above the minimum pressure required to fill the 

breathing bag, within the breathing resistance requirements for the apparatus. 

Note: The range allowed after a test tolerance is 0.28" H2 O to 0.75"H2 O. All values must fall 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 7 of 14 

within this range. 

(2) The relief valve or system shall be designed to prevent external atmospheres from 

entering the breathing circuit. 

(3) The relief valve or system shall be designed to permit manual overriding for test 

purposes and in the event of a failure in the valve or system. 

7. RECORDS\TEST SHEETS

7.1. All test data will be recorded on the SAFETY RELIEF VALVE OPERATION, 

CLOSED-CIRCUIT, SELF-CONTAINED BREATHING APPARATUS test data sheet. 

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

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. 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 8 of 14 

SAFETY RELIEF VALVE OPERATION, CLOSED-CIRCUIT, 

SELF-CONTAINED BREATHING APPARATUS

Project No : Date: __________ 

Company : ___________________________________________ 

Respirator Type : ___________________________________________ 

Reference: 42 CFR, Part 84, Subpart H, 84.84(i)(1)(2)(3). 

Requirement: The relief valve or system shall operate automatically when the pressure in the breathing 

circuit on the inhalation side of the breathing bag reaches 13 mm. (one-half inch) watercolumn height of pressure above the minimum pressure required to fill the breathing bag, 

within the breathing resistance requirements for the apparatus. 

Results: Unit #1 

Test # Bag Full (inches H2O) Release (inches H2O) Difference (inches H2O) 

1. ____________________ 

2. ____________________ 

3. ____________________ 

4. ____________________ 

5. ____________________ 

6. ____________________ 

Comments : 

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________ 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 9 of 14 

Results: Unit #2 

Test # Bag Full (inches H2O) Release (inches H2O) Difference (inches H2O) 

1. ____________________ 

2. ____________________ 

3. ____________________ 

4. ____________________ 

5. ____________________ 

6. ____________________ 

Comments : 

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________ 

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________ 

Test Engineer: PASS FAIL________ 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 10 of 14 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 11 of 14 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 12 of 14 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 13 of 14 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 
Procedure No. RCT-ASR-STP-0138 Revision: 1.1 Date: 26 September 2005 Page 14 of 14 

Revision History 

Revision Date Reason for Revision 

1.0 21 February 

2000 

Historic document 

1.1 26 September 

2005 

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

No changes to method 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy 

Uncontrolled Copy 

 Uncontrolled Copy