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-APR-STP-0041 Revision: 1.1 Date: 29 June 2005

DETERMINATION OF HYDROGEN CYANIDE SERVICE LIFE TEST, 

AIR-PURIFYING RESPIRATORS 

 STANDARD TESTING PROCEDURE (STP) 

1. PURPOSE

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

hydrogen cyanide service life requirements on escape gas masks air-purifying respirators 

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 I, Section 84.110(c); Volume 60, Number 110, June 8, 1995. 

2. GENERAL

This STP describes the Determination of Hydrogen Cyanide Service Life Test, Air-Purifying 

Respirators 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/MATERIAL

3.1. The list of necessary test equipment and materials follows: 

 3.1.1. Miller Nelson Research Model 401 Flow-Temperature-Humidity Control System 

or equivalent. 

 3.1.2. Interscan Corporation Model 1288 Hydrogen Cyanide detector or equivalent. 

 3.1.3. Certified cylinder of 5 parts per million (ppm) HCN, balance gas Nitrogen. 

 3.1.4. Certified cylinder of 50 parts per million (ppm) HCN, balance gas Nitrogen. 

 3.1.5. Tylan mass flow meter and controller or rotameter, 10 lpm flowrate. 

 3.1.6. Gilian Gil-Air-3 Sampling Pump, or equivalent. 

 3.1.7. Vaisala model HMI 31 humidity indicator.

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Procedure No. RCT-APR-STP-0041 Revision: 1.1 Date: 29 June 2005 Page 2 of 11 

 3.1.8. Hydrogen Cyanide cylinders, 5% hydrogen cyanide, balance gas of helium. Due 

to the extreme toxicity of hydrogen cyanide gas, cylinders of 5% hydrogen 

cyanide with a balance gas of helium are preferred. Depending on the size and 

volume of the cylinders, several (6-10) may be required to complete testing due 

to the volume of gas being delivered to the system. 

 3.1.9. Electronic balance with accuracy of 0.001 grams (g). 

3.2. Test fixture for mounting canisters. The test fixture used is specific to each manufacturer 

depending on how the canister is mounted to the facepiece. Canisters are tested with 

their connections glued into the ground glass joint. 

3.3. The test chamber consisting of a 12" x 111⁄2" x 7" air tight box, made of 1⁄2" plexiglass 

with 2 hinge type locks on the door opening lined with gasket material. A 1⁄2" hole is 

located on the back of the test chamber for the introduction of the test concentration and a 

11⁄2" hole on the top for the exit of the test fixture and to detect the breakthrough 

concentration. This fixture is not commercially available. 

3.4. Resistance tester consisting of a vacuum source capable of delivering 85 liters per minute 

(lpm), a 6-inch slant manometer, and a 29/42 female ground glass joint. The resistance 

testers currently being used are located on the silica dust chamber. 

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

described in the current ALOSH Facility Laboratory Safety Manual. 

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

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

equipment. 

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

must wear special gloves which protect against lacerations or punctures. 

4.3. HYDROGEN CYANIDE BENCH TEST FOR ESCAPE GAS MASKS. 

 4.3.1. Three "as received" canisters will be tested at 64 lpm, continuous air flow, 

50 + 5 percent relative humidity (RH), approximately 25o

C, containing 5000 ppm 

HCN. 

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Procedure No. RCT-APR-STP-0041 Revision: 1.1 Date: 29 June 2005 Page 3 of 11 

 4.3.2. Two canisters will be equilibrated at room temperature by passing 25 percent RH 

air through them at 64 lpm for 6 hours and then testing them at 50 percent RH, 

approximately 25o

C, and 64 lpm continuous air flow rate containing 5000 ppm 

HCN. 

 4.3.3. Two canisters will be equilibrated at room temperature by passing 85 percent RH 

air through them at 64 lpm for 6 hours and then testing them at 50 percent RH, 

approximately 25o

C, and 64 lpm continuous air flow rate containing 5000 ppm 

HCN. 

 4.4 Please refer to Material Safety Data Sheets and the NIOSH Health and Safety 

Manual for the proper protection and care in handling, storing, and disposing of the 

chemicals and gases used in this procedure.

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. Follow individual instruction manuals for set up and maintenance of equipment used in 

this procedure prior to beginning testing. Malfunctioning equipment must be repaired or 

replaced and properly set up and calibrated before starting all tests. 

 5.2. After the manufacturer's specified warmup period, calibrate the HCN analyzer on the low 

scale setting using the certified gas cylinder containing the 5 ppm standard and the high 

scale setting using the 50 ppm certified gas cylinder as follows: 

5.2.1 With a tee in line on the gas cylinder, insert the intake tubing from the analyzer 

into the tee. 

5.2.2 Turn on the certified hydrogen cyanide cylinder for each calibration point 

needed. 

5.2.3 Wait till the reading stabilizes for each calibration point, and adjust the span 

control to read analysis of the cylinder. 

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Procedure No. RCT-APR-STP-0041 Revision: 1.1 Date: 29 June 2005 Page 4 of 11 

 5.3. Calculate the volume of 5% HCN required to produce a 5000 ppm concentration in 64 

lpm continuous airflow using the formula: 

 C1V1 = C2V2 

 Where 

 C1= concentration of 5000 ppm (0.5%) in 64 lpm air 

 V1= volume of air in lpm 

 C2= 50,000 ppm (5.0 %) HCN 

 V2= volume of air in lpm 

 (0.5% HCN) x 64 lpm air = 5% HCN x V2

 V2 = 0.5 x 64

 5 

 V2= 6.4 lpm 5% HCN 

 

 64 lpm air - 6.4 lpm 5% HCN = 57.6 lpm air 

Therefore, using the above calculation, 6.4 lpm of 5% Hydrogen cyanide in 57.6 lpm air 

should produce a test concentration of 5000 ppm HCN. 

 5.4. Set up test equipment as shown in Figure 1. In addition to the humidity reading 

controlled by the Miller Nelson system, the Vaisala HMI 31 humidity indicator sensor is 

inserted into the air stream via a tee set-up directly prior to the introduction of the gas. 

This set up is not shown on Figure 1. The humidity reading obtained at this point takes 

into account tubing length and outside hood air temperature. 

 5.5. Turn on: 

 5.5.1. Miller Nelson Unit. 

 5.5.2. Air and water supplies. 

 5.6. Adjust and calibrate air flow of Miller Nelson Unit to 57.6 lpm air. 

 5.7. Adjust flow controller or rotameter to desired setting of 6.4 lpm HCN. 

 5.8. Direct test concentration into the test chamber equipped with a scrubber canister. 

 5.9. Verify the challenge test concentration via a dilution factor method by drawing off 1 lpm 

test concentration and diluting with a known volume of clean air. By adjusting the flow 

controller and noting the deflection on the calibrated analyzer, the test concentration can 

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Procedure No. RCT-APR-STP-0041 Revision: 1.1 Date: 29 June 2005 Page 5 of 11 

 be determined. The volume of clean air required to dilute the 1 lpm of challenge 

concentration to produce 5000 ppm is calculated as follows: 

 5.9.1. C1V1 = C2V2 Where C = concentration and V = volume 

 

 5000 ppm x 1 lpm = 50 ppm x V2 

 V2 = 5000 

 50 

 V2 = 100 

 Therefore: V2 - V1 = volume of clean air 

 5.10. Draw off 1 lpm of the hydrogen cyanide in air test concentration and dilute it with the 

calculated volume of clean air for the required concentration. 

 5.11. Insert the intake tubing from the analyzer into the dilution air/gas stream. Adjust the 

flowmeter until the analyzer reads 50 ppm. Note the reading of the Tylan flowmeter for 

the concentration being determined. 

 5.11.1. As an example: A reading of 50 ppm for the dilution of 99 lpm/1 lpm HCN 

concentration results in a factor of 100. By using the following formula the total 

HCN test concentration can be determined. 

 Dilution factor x 50 ppm reading = Total HCN test concentration 

5.12. Once the test concentration has been established, testing may begin. 

5.13. Weigh the canister and record the weight. 

5.14. Take inhalation and exhalation resistances of the cartridge or canister mounted on the 

facepiece at 85 lpm. See Sections 84.122, Title 42, Code of Federal Regulations, Part 84 

for breathing resistance requirements. 

5.15. Mount canister onto test fixture and place in testing chamber. 

 5.16. Direct challenge concentration airflow into test chamber. Start timer. Mount small piece 

of tygon tubing onto the outlet of the test fixture. Insert intake tubing of detector into a 

slit cut into the side wall of the tubing to allow the detector to sample at the flow rate of 

the detector without interference from airflow back pressure. Monitor and record 

upstream and downstream temperatures throughout testing. Record breakthrough values 

and times. 

5.17. Run test until breakthrough of 4.7 ppm is observed or minimum service life is surpassed. 

5.18. Dismount canister, weigh and record final weight, and take final inhalation and 

exhalation resistances. 

5.19. Shut off hydrogen cyanide cylinder. 

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Procedure No. RCT-APR-STP-0041 Revision: 1.1 Date: 29 June 2005 Page 6 of 11 

5.20. Disconnect hydrogen cyanide tubing from the rotameter to prevent contamination the 

humidity sensor. 

5.21. Allow clean air to purge through system for 10 - 15 minutes. 

5.22. Turn off air and water supply to Miller Nelson system and shut off unit. 

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 I, Section 84.110(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. 

 84.110 Gas masks; description. 

(c) Gas masks for respiratory protection against gases and vapors other than those 

specified in paragraph (b) of this section, may be approved upon submittal of an 

application in writing for approval to the Respirator Branch listing the gas or vapor and 

suggested maximum use concentration for the specific type of gas mask. The Institute 

will consider the application and accept or reject it on the basis of effect on the wearer's 

health and safety and any field experience in use of gas masks for such exposures. If the 

application is accepted, the Institute will test such masks in accordance with the 

requirements of this subpart. 

7. RECORDS/TEST SHEETS

7.1. All test data will be recorded on the HYDROGEN CYANIDE SERVICE LIFE 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. 

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Procedure No. RCT-APR-STP-0041 Revision: 1.1 Date: 29 June 2005 Page 7 of 11 

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-SOP-0005-00. 

8. ATTACHMENTS

 8.1 Bench Top Set-Up. 

 8.2 Data Sheet. 

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Procedure No. RCT-APR-STP-0041 Revision: 1.1 Date: 29 June 2005 Page 8 of 11 

 Figure 1

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Procedure No. RCT-APR-STP-0041 Revision: 1.1 Date: 29 June 2005 Page 9 of 11 

RB - RESPIRATOR CERTIFICATION TEAM 

 GAS & VAPOR RESPIRATOR TEST DATA SHEET (Ref.33-48,50,62) STP No.: [ ] 

 Task Number: TN- Gas Name: 

Manufacturer: Item Tested: 

RESISTANCE Maximum Allowable Resistance 

 (mm of H2O) 

 Actual Resistance 

 (mm of H2O) 

 Inhalation Exhalation Inhalation Exhalation 

 Test 

 Initial Initial 

Final 

 I

nitial Final 

 Result 

 1 

 2 

 3 

 4 

 5 

 6 

 7 

 Overall Results: Pass Fail Comment: 

WEIGHTS WEIGHTS (gm) AIRFLOW (Lpm)

 AND 

 AIRFLOWS Test Rate (PAPR Only)

 Test 

Con'd 

 

Conc. 

(ppm) RH% Lpm 

 I

nitial Final 

 1 

 2 

 3 

 4 

 5 

 6 

 7 

 Overall Results: Pass Fail Comment: 

DATA TABLE Temperature (oC) 

 Test 

 Test 

 Cond. 

 Final 

 Time (min) 

 Leakage 

 (ppm) 

 Dnst

ream 

 Upstre

am 

 Corrected 

 Time (min) 

 1 

 2 

 3 

 4 

 5 

 6 

 7 

 Overall Results: Pass Fail Comment: 

 Was all testing equipment in calibration throughout all testing: Yes No 

 Signature: Date: 

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Procedure No. RCT-APR-STP-0041 Revision: 1.1 Date: 29 June 2005 Page 10 of 11 

RB - RESPIRATOR CERTIFICATION TEAM Page 2 

 GAS & VAPOR RESPIRATOR TEST DATA SHEET (Ref.33-48,50,62) STP No.: [ ] 

 Task Number: TN- Gas Name: 

Manufacturer: Item Tested: 

 

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Procedure No. RCT-APR-STP-0041 Revision: 1.1 Date: 29 June 2005 Page 11 of 11 

Revision History 

Revision Date Reason for Revision 

1.0 12 March 2002 Historic document 

1.1 29 June 2005 Update header and format to reflect lab move from Morgantown, WV 

No changes to method 

 

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