NACE STD TM0187-1998.pdf

NACE Standard TMO187-98 Item No. 21220 THE C O R R O S I O N S O C I E T Y

Standard Test Method Evaluating Elastomeric Materials in Sour Gas Environments This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone, whether he has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard. Nothing contained in this NACE International standard is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent. This standard represents minimum requirements and should in no way be interpreted as a restriction on the use of better procedures or materials. Neither is this standard intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this standard in specific instances. NACE International assumes no responsibility for the interpretation or use of this standard by other parties and accepts responsibility for only those official NACE International interpretations issued by NACE International in accordance with its governing procedures and policies which preclude the issuance of interpretationsby individual volunteers. Users of this NACE International standard are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this standard prior to its use. This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this standard. Users of this NACE International standard are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this standard. CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE International requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication. The user is cautioned to obtain the latest edition. Purchasers of NACE International standards may receive current information on all standards and other NACE International publications by contacting the NACE International Membership Services Department, P.O. Box 218340, Houston, Texas 77218-8340 (telephone +I [281]228-6200). Reaffirmed 1998-03-24 Revised April 1992 Approved January 1987 NACE Intemational F.O.Box 218340 Houston, Texas 77218-8340 +1 (281)228-6200 ISBN 1-57590-056-4 O 1998, NACE International

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Foreword This standard test method was prepared to serve as a tool in the process of evaluating elastomeric materials for use in the oilfield and other energy-related areas where sour gaseous environments are encountered. It is an accelerated aging procedure similar to ASTM'" 471,l with additional information on sour environment testing under pressures greater than atmospheric pressure. It is intended for use by anyone investigating the use of elastomeric materials in sour gas environments. By using the specified test conditions, data from separate laboratories that utilize this test method may be compared. No technical organization is known to have issued a comparable standard test method. This method is useful in conducting research and development of elastomeric vulcanites. This standard was originally prepared in 1987 and revised in 1992 by Task Group T-1G-17, a component of Unit Committee T-1G on Protective Coatings, Elastomers, and Other Nonmetallic Materials for Oilfield Use. It was reaffirmed by T-1G in 1998 and is published by NACE International under the auspices of Group Committee T-1 on Corrosion Control in Petroleum Production. These committees are composed of industry representatives including consumers, producers, and interested individuals.

In NACE standards, the terms shall, must, should, and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual, 3rd. ed., Paragraph 8.4.1.8. Shall and must are used to state mandatory requirements. Should is used to state that which is considered good and is recommended but is not absolutely mandatory. May is used to state that which is considered optional.

("American Society for Testing and Materials (ASTM), 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959.

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Standard Test Method Evaluating Elastomeric Materials in Sour Gas Environments Contents 1. General..................................................................................................................... 2. Definitions................................................................................................................. 3. Reagents .................................................................................................................. 4 . Test Media................................................................................................................ 5. Test Conditions ......................................................................................................... 6. Test Specimens ........................................................................................................ 7. Test Equipment......................................................................................................... 8. Test Procedures........................................................................................................ 9. Reporting of Test Results.......................................................................................... References..................................................................................................................... Appendix A - Safety Consideratons in Handling H2S .................................................... Table A.l -Toxicity of H2S...........................................................................................

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Section 1: General 1.1 This standard establishes a test method to measure the ability of elastomeric materials to withstand static exposure to elevated pressure and vapor phase sour gas environments, e.g., gaseous hydrocarbons with hydrogen sulfide (H2S), and is not designed to be an immersion or a functional test. It is designed for testing O-rings or specimens of elastomeric vulcanites cut from standard sheets (see ASTM D 31822). This test method is not applicable to the testing of cellular rubber or porous materials.

1.2 This standard recommends procedures for the preparation of test specimens and equipment to be used, the test procedures to be followed, and procedures for reporting results. The standard also discusses test conditions, test media, and reagents. In summary, the standard specifies conditions of temperature, exposure time, and pressure for the exposure of test specimens to the influence of a gas. This gaseous environment contains H2S, carbon dioxide (COZ), methane (CH4), water vapor, and liquid hydrocarbon vapor. The results are determined by monitoring changes in physical and mechanical properties (¡.e., mass, volume, compression set, hardness, tensile strength, ultimate elongation, and modulus), as well as changes in appearance after exposure to the selected test medium.

1.3 In view of the wide range of service conditions, this test method is intended to be a means only of initial material evaluation and is not intended to provide any direct correlation with service performance. No attempt is made or implied to establish any pass/fail criteria for materials tested by this method. The change in properties of an elastomeric material is indicative of its resistance to the specific environment. The test can be regarded only as a measure of the resistance under the conditions of this particular test and not necessarily as having any direct relation to service value. The significance of the results can be determined only by each laboratory for its particular application. The precision of this test method and reproducibility within and among laboratories has not been established. Test specimens being tested using this method may be different in Performance or alike within test error. The user of this method is encouraged to establish statistical significance of the data resulting from use of this method. 1.4 Safety Precautions: H2S is an extremely toxic gas that must be handled with care. See Appendix A for safety considerations and information on toxicity of this gas.

Section 2: Definitions 2.1 ASTM D 15663provides definitions of technical terms used in this standard.

Section 3: Reagents 3.1 Reagent Purity

3.1.2 The hydrocarbon liquids (n-hexane, n-octane, n-decane, and toluene) shall be reagent grade.

3.1.1 The gases ( H S , COZ,CH4) shall be reagent or chemically pure (99.5% minimum purity) grade. The nitrogen or other inert gas used for purging (to remove oxygen from the test environment) shall be of high-purity, oxygen-free grade (¡.e., less than 5 ppm oxygen).

3.1.3 The water shall conform to ASTM D 11934 for Type IV reagent water. Tap water shall not be used.

Section 4: Test Media 4.1 It is usually desirable to evaluate elastomers in the

specific environments to which they will be exposed in service. However, to provide a basis for the evaluation of

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elastomer performance, the gas phase shall have one of the following compositions, the use of which will depend on the elastomer to be tested and the service conditions

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TM0187-98 anticipated. The observed performance of elastomeric materials in service is highly dependent on the particular physical nature and chemical composition of the service environment. Any change in the water, hydrocarbon, and/or gas composition can significantly change the test resuIt s. 4.2 Test Environment 4.2.1 The composition of the gas phase shall be one of the following. The composition of the gas phase shall be one of the following: 4.2.1.1 20 I2 vol% H,&, 5 i1 vol% Con, 75 13 vol% CH4.

4.2.1.2 5 11 vol% HzS, 20 12 Vol% COZ, 75 13 vol% CH4. 4.2.2 The composition of the hydrocarbon liquid phase shall be as follows: Hvdrocarbon n-hexane n-octane n-decane toluene

Vol% 25 11 20 I1 50 11 5 10.5

The hydrocarbon liquid phase shall be mixed prior to being charged in the test vessel.

Section 5: Test Conditions 5.2 Test Pressure

5.1 Test Temperature 5.1.1 The user shall select one of the following temperatures that is most appropriate for the elastomer tested and the anticipated service conditions.

5.2.1 The final test pressure, after heating to the test temperature, shall be 6.9 10.7 MPa (1,000 1100 PW. 5.3 Test Exposure Period

5.1.1.1 100°C (212°F) 5.3.1 The standard test exposure period shall be 100 I2 h.

5.1.1.2 175°C (347°F) 5.1.2 The selected test temperature shall maintained within I 3°C (&OF).

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5.3.2 The test exposure period shall be defined as the period elapsed from the time the test pressure and test temperature are established until the test pressure is discontinued.

Section 6: Test Specimens 6.1 The selection of the test specimen is often restricted by the size and shape of the available material. The geometry, cross-sectional area, and orientation of the test specimen can affect the test results and must be recorded. 6.2 Standard O-Ring Test Specimen 6.2.1 The standard test specimen shall be an O-ring with 37.47 mm ID and 5.33 mm cross-sectional diameter (1.475 in. ID and 0.210 in. cross-sectional diameter). This corresponds to a standard AS 568A325’ O-ring. 6.3 For materials that cannot be tested in O-ring form, the test specimen shall be of sheet form with a thickness of 2.0 10.2 mm (0.080 10.008 in.).

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6.3.1 Sheet test specimens to measure change in mass and volume shall be 25 by 51 by 2.0 4 . 2 mm (1.O by 2.0 by 0.080 4.008 in.). 6.3.2 Sheet test specimens to measure change in tensile strength, ultimate elongation, modulus, and hardness shall be prepared from flat 2.0 10.2 mm (0.080 I0.01 in.) thick sheet using Die C (see ASTM D 4126). 6.3.3 Compression set test specimens shall be cylindrical disks 12.5 10.5 mm (0.49 10.02 in.) thick and 29.0 10.5 mm (1.14 10.02 in.) in diameter. The disks may be direct molded, plied from disks cut from vulcanized sheets, or taken from actual parts.

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Section 7: Test Equipment 7.1 Test Vessels 7.1.1 Many types of test vessels are acceptable for the exposure of elastomers to H2S environments. Consequently, the discussion in this section is intended to emphasize the features of this equipment that are necessary for safe and reliable tests. 7.1.2 Test vessels shall be capable of being purged to remove oxygen before the test is initiated and retain the pressurized test environment during the test exposure period. 7.1.3 The size of the test vessel shall be such that the ratio of the test vessel volume to total test specimen volume is greater than 25 to 1. This requirement is intended to standardize the rate of consumption of the various constituents in the test media. 7.1.4 One important consideration for testing is the interaction of the test media with the materials used in the construction of the test vessel. For tests involving Has, the test vessel must be able to withstand both mass-loss corrosion and embrittlement by the test media. 7.1.4.1 The test vessel shall be inert to the test media, the test specimens, and potential test specimen decomposition products. In HzS testing, it is important to select construction materials that will minimize the corrosion that tends to consume the constituents of the test media and contaminate the test media. Also, localized corrosion (Le., pitting and crevice

corrosion), in addition to general mass-loss corrosion, can result in unexpected loss of pressure-sealing capabilities or failure. 7.1.4.2 The test vessel shall be designed to operate continuously at pressures of at least those specified in this standard (see Paragraph 5.2.1) without exhibiting environmental cracking in the H2S-containing environments. (See NACE Standard MRO175’ for information to aid in selecting construction materials.) Manufacturers of autoclaves, valves, and fittings should also be consulted for additional information on the proper selection of the materials for the test vessel. 7.2 Test Fixture 7.2.1 Special fixtures are required to support the test specimens and to prevent direct contact with the test vessel walls, the liquids as they are introduced to and removed from the test vessel, the liquid phase in the bottom of the test vessel, or other test specimens. The elastomeric material test specimens shall be exposed to the gas phase only. 7.2.2 The compression set test fixtures shall meet the requirements specified in ASTM D 14148 and D 395’ (Method B). 7.2.3 All fixtures exposed to the test media shall be compatible with the test media and test specimens. The design and selection of materials shall conform to Paragraph 7.1.4.

Section 8: Test Procedures 8.1 The test procedures in this standard provide for the determination of compression set as well as for the determination of change in mass and/or volume, tensile properties (tensile strength, ultimate elongation, and modulus), and hardness as a result of exposure of the test specimens to the test media. The exposure testing sequence is detailed in Paragraph 8.7. 8.1.1 Each test run shall be limited to the evaluation of only one elastomeric material compound. Interactions between different compounds can occur when they are tested together, and this must be avoided.

8.2.1 Prior to testing, the test specimens shall be equilibrated at a temperature of 22 &OC (72 &OF) and 50 15% relative humidity for a period of at least 24 h. 8.2.2 The cross-section of each test specimen shall be measured after equilibration. 8.3 Change in Mass and Volume 8.3.1 A minimum of three test specimens of a single compound must be tested.

8.2 Test Specimen Preparation

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TMO187-98 8.3.2 Each test specimen must be weighed in air (M,) and in distilled or deionized water (Ma) to the nearest 1 mg before testing. 8.3.3 After exposure to the test media and return to ambient conditions, each test specimen must be reweighed in air (M2) and in distilled or deionized water (M4) to the nearest 1 mg. 8.3.4 The change in mass (AM) shall be calculated using Equation (i).

AM(%) = M 2 - M l

MI 8.3.5 The change in volume (AV) shall be calculated

using Equation (2).

8.3.6 If the water displacement method for determining volume change is unsatisfactory, the volume change may be calculated by using an appropriate mensuration formula before and after exposure to the test media.

8.5 Change in Hardness 8.5.1 The hardness shall be determined in accordance with ASTM D 14151° or D 2240.11 (NOTE: For the purpose of this test using Standard AS 568-325, the ASTM size requirement is waived to allow the reporting of hardness in Shore Durometer.) 8.5.2 The initial hardness and the hardness following exposure may be measured on the test specimens used to determine the tensile properties. However, tensile property tests shall be conducted before hardness is measured so that any surface defects induced by the hardness measurement will not influence the tensile test results. 8.6 Compression Set 8.6.1 Compression set shall be determined in accordance with ASTM D 1414 and D 395 (Method B). 8.6.2 For exposure to the test media, the O-ring test specimen shall be sectioned or cut and the compression set fixture vented. This venting is to prevent entrapment of air inside the O-ring. 8.6.3 A minimum of three test specimens of a single compound shall be tested in conjunction with exposure to the test media.

8.4 Change in Tensile Properties 8.4.1 The tensile properties of the elastomeric material shall be determined in accordance with ASTM D 1414 and D 412. 8.4.2 The properties measured shall be tensile strength, ultimate elongation, and modulus (when applicable) at 25, 50, and 100% elongation. 8.4.3 The original tensile properties shall be determined using three test specimens from the same batch used for the exposure tests. 8.4.4 A minimum of three test specimens of a single compound shall be exposed to the test media to determine the effect of the test media on the tensile properties. 8.4.5 Following exposure to the test media and return to ambient conditions, each test specimen shall be tested in air using the original unexposed thickness or cross-sectional area of the test specimens in the calculations. 8.4.6 The change in tensile properties from the initial value to that resulting from the exposure to the test media shall be determined. The change shall be reported in terms of percent change in property.

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8.6.4 Following exposure to the test media and return to ambient conditions, the compression set of each test specimen shall be determined in accordance with ASTM D 1414 and D 395 (Method B). 8.7 Exposure Testing Sequence 8.7.1 The test specimens measured and weighed for determination of change in mass, volume, tensile properties, and/or hardness shall be placed in the test vessel along with the compression set test specimens and fixture. Each test specimen shall be supported inside the test vessel in accordance with Paragraph 7.2.1. 8.7.2 The test vessel shall be charged with a quantity of the premixed hydrocarbon liquid phase (specified in Paragraph 4.2.2) equal to 5% of the test vessel volume. A quantity of water (specified in Paragraph 3.1.3) equal to 5% of the test vessel volume shall then be charged. These liquids shall be placed into and removed from the test vessel in such a manner that they will not contact the test specimens. 8.7.3 The test vessel shall then be sealed and purged with inert gas (nitrogen or argon is recommended). The purge shall be accomplished by

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TMOI 87-98 charging the test vessel to 340 to 690 kPa (50 to 100 psig) with the inert gas and then venting the test vessel to atmospheric pressure. This pressurization/ venting cycle shall be performed three times to remove most of the oxygen from the test vessel. 8.7.4 The test vessel shall be pressurized with the gaseous HzS-containing environment as specified in Paragraph 4.2.1. The initial pressurization level shall be such that it will result in the specified test pressure of 6.9 10.7 MPa (1,000 1100 psig) at test temperature. 8.7.4.1 When necessary, a gas intensifier or pump may be used to attain the total test pressure. 8.7.5 The test vessel shall be heated to the selected test temperature within a period of 4 h. 8.7.6 The test vessel shall be maintained at the designated test temperature and test pressure for the entire test exposure period. 8.7.7 Depressurization of the test vessel shall begin at the completion of the specified test exposure period and while maintaining the test temperature.

8.7.10 The cooled test vessel shall then be purged with nitrogen to remove the remaining H2S prior to opening the test vessel to remove the test specimens. 8.7.10.1 The test specimens shall not be removed from the test vessel until the test vessel has cooled to a temperature of 38°C (100°F) maximum and the H2S has been purged from the test vessel. 8.7.11 The removed test specimens shall be cleaned by immersion in 95% ethyl alcohol for approximately 2 s and then patted dry. 8.7.12 All test specimens shall be evaluated for properties at room temperature within 2 h from the time they are removed from the test vessel. The sequence of evaluation shall be as set forth in Paragraphs 8.7.12.1 through 8.7.12.7. 8.7.12.1 Weigh test specimens within 10 min of removal from the test vessel to determine change in mass. 8.7.1 2.2 Weigh and/or measure test specimens to determine change in volume.

8.7.8 The gas pressure in the test vessel must be released slowly to prevent damage to the test specimens and allow proper disposal of the HzS vented from the test vessel. One of the following two alternative methods may be used to accomplish this slow release.

8.7.12.3 Remove compression set test specimens from fixture.

8.7.8.1 Release the gas pressure at approximately a constant rate, not to exceed 140 kPa (20 psig) per min.

8.7.12.5 Measure tensile properties of test specimens in accordance with ASTM D 412.

8.7.8.2 Release the gas pressure in a stepwise manner in 690-kPa (100-psig) increments. The pressure shall be held for a minimum of 5 min between increments to permit test specimen degassing.

8.7.12.4 Measure thickness of compression set test specimens in accordance with ASTM D 395 (Method B).

8.7.12.6 Measure hardness of test specimens in accordance with ASTM D 1415 or ASTM D 2240. 8.7.12.7 Conduct a visual inspection of test specimens, which may include magnified or microscopic examination.

8.7.9 After depressurization, the test vessel must be cooled to a maximum temperature of 38°C (IOOOF) within a period of 6 h.

Section 9: Reporting of Test Results 9.1 The test results report shall state that the test was conducted in accordance with this NACE standard. The following shall be reported:

9.1.1 Batch number, manufacturer, polymer type, compound number, and date of vulcanization of the test specimens as supplied by the manufacturer.

9.1.2 Type of test specimen used.

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TMO187-98 9.1.3 Dates of the test exposure periods.

9.1.8 Temperature of testing room on dates of test exposure periods.

9.1.4 Test media composition. 9.1.9 Other pertinent observed and recorded data. 9.1.5 Temperature of exposure. 9.1.10 Calculated results. 9.1.6 Pressure of exposure. 9.1.1 1 Statement of conditions of the exposed test specimens.

9.1.7 Test exposure periods.

9.1.12 Test method used to determine hardness.

References 1. ASTM D 471 (latest revision), “Standard Test Method for Rubber Property - Effect of Liquids” (West Conshohocken, PA: ASTM).

9. ASTM D 395 (latest revision), ”Standard Test Methods for Rubber Property - Compression Set” (West Conshohocken, PA: ASTM).

ASTM D 3182 (latest revision), “Standard Practice for Rubber - Materials, Equipment, and Procedures for Mixing Standard Compounds and Preparing Standard Vulcanized Sheets” (West Conshohocken, PA: ASTM).

10. ASTM D 1415 (latest revision), “Standard Test Method for Rubber Property - International Hardness” (West Conshohocken, PA).

2.

ASTM D 1566 (latest revision), “Standard Terminology Relating to Rubber“ (West Conshohocken, PA: ASTM). 3.

4. ASTM D 1193 (latest revision), “Standard Specification for Reagent Watet‘ (West Conshohocken, PA: ASTM). 5. AS 568A (latest revision), ”Aerospace Size Standard for O-Rings” (Warrendale, PA: SAE). 6. ASTM D 412 (latest revision), “Standard Test Methods for Vulcanized Rubber and Thermoplastic Rubbers and Thermoplastic Elastomers - Tension” (West Conshocken, PA: ASTM). 7. NACE Standard MRO175 (latest revision), “Sulfide Stress Cracking Resistant Metallic Materials for Oilfield Equipment” (Houston, TX: NACE International).

11. ASTM D 2240 (latest revision), “Standard Test Method for Rubber Property - Durometer Hardness” (West Conshohocken, PA: ASTM). 12. OSHA Rules and Regulations, Federal Register, CFR 29, Part 191O. 1000, 1996.

13. N. Irving Sax, Dangerous Properties of Industrial Materials (New York, NY: Reinhold Book Corp., 1984). 14. Documentation of the Threshold Limit Values (Cincinnati, OH: American Conference of Governmental Industrial Hygienists, Inc.) 15. NIOSH/OSHA, Occupational Health Guidelines for Chemical Hazards, Publication NU 81-123 (Washington, DC: Superintendent of Documents, U.S. Government Printing Office).

8. ASTM D 1414 (latest revision), “Standard Test Methods for Rubber O-Rings” (West Conshohocken, PA: ASTM) .

(*)Societyof Automotive Engineers (SAE), 400 Commonwealth Dr., Warrendale, FA 15096.

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Appendix A

-Safety Considerations in Handling H2S

Toxicity

Fire and Exposure Hazards

HzS is perhaps responsible for more industrial poisoning accidents than any other single chemical. A number of these accidents have been fatal. HzS shall be handled with caution and any experiments using it shall be planned carefully. The maximum allowable Occupational Safety and Health Administration (OSHA)(3’ concentration of HzS in the air for an eight-hour work da is 20 ppm, well above the level detectable by smell. However, the olfactory nerves can become deadened to the odor after exposure of 2 to 15 min, depending on concentration, so that odor is not a completely reliable alarm system. Briefly, the following are some of the human physiological reactions to various concentrations of HzS. Exposure to concentrations in the range of 150 to 200 ppm for prolonged periods may cause edema of the lungs. Nausea, stomach distress, belching, coughing, headache, dizziness, and blistering are symptoms of poisoning in this range of concentration. Pulmonary complications such as pneumonia are strong possibilities from such subacute exposure. At 500 ppm, unconsciousness may occur in less than 15 min and death within 30 min. At concentrations above 1,000 ppm, a single inhalation may result in instantaneous unconsciousness, complete respiratory failure, cardiac arrest, and death. Additional information on the toxicity of HzS can be obtained by consulting the Material Safety Data Sheet provided by the manufacturer or distributor and from consulting sources such as Dangerous Properties of Industrial Materials by N. Irvin Sax,13 Documentation of the Threshold Limit Values,” and the NIOSHiOSHA Occupational Health Guidelines for Chemical Hazards.”

HzS is a flammable gas, yielding poisonous sulfur dioxide as a combustion product. In addition, its explosive limits range from 4 to 46% in air. Appropriate precautions shall be taken to prevent these hazards from developing.

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(3)Occupational Safeíy and Health Administration (OSHA), 200

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Recommended Safety Procedures During Testing All tests shall be performed in a hood with adequate ventilation to exhaust all HzS. The HzSflow rates shall be kept low to minimize the quantity exhausted. A 10% caustic absorbent solution for effluent gas can be used to further minimize the quantity of HzS gas exhausted. This solution will need periodic replenishing. Provision should be made to prevent backflow of the caustic solution into the test vessel if the H2S flow is interrupted. Suitable safety equipment shall be used when working with H2S. Because the downstream pressure frequently rises as corrosion products, debris, etc., accumulate and interfere with regulation at low flow rates, particular attention should be given to the output pressure on the pressure regulators. Gas cylinders shall be securely fastened to prevent tipping and breaking of the cylinder head. Because HzS is in liquid form in the cylinders, the high-pressure gauge should be checked frequently. Relatively little time will elapse after the last liquid evaporates and the pressure drops from 1.4 MPa (200 psi) to atmospheric pressure. The cylinder should be replaced by the time it reaches 0.5 to 0.7 MPa (75 to 100 psi) because the regulator control may become erratic. Flow must not be allowed to stop without closing a valve or disconnecting the tubing at the test vessel because the solution will continue to absorb HzS and move upstream into the flowline, regulator, and even the cylinder. A check valve in the line should prevent the problem if the valve works properly. However, if such an accident occurs, the remaining HzS must be vented as rapidly and safely as possible and the manufacturer notified so that the cylinder can be given special attention.

Constitution Ave. NW, Washington, DC 2021O.

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PPm (Parts Per million)

0-2 min

2-15 min

Table A.l

-Toxicity of H2S

15-30 min

30 min to 1 h

1-4 h

4-8 h

8-48 h

Mild conjunctivitis; respiratory tract irritation

5-1O0

100-150

Coughing; irritation of eyes; loss of sense of smell

Disturbed respiration; pain in eyes; sleepiness

Throat irritation

Salivation and mucous discharge; sharp pain in eyes; coughing

Increased symptomstA)

Hemorrhage and death(AJ

150-200

Loss of sense of smell

Throat and eye irritation

Throat and eye irritation

Difficult breathing; blurred vision; light shy

Serious irritating eff e d A J

Hemorrhage and death(A)

250-350

Irritation of eyes; loss of sense of smell

Irritation of eyes

Painful secretion of tears; weariness

Light shy; nasal catarrh; pain in eyes; difficult breathing; conjunctivitis

Hemorrhage and death(A'

350-450

Irritation of eyes; loss of sense of smell

Difficult respiration; coughing; irritation of eyes

Increased irritation of eyes and nasal tract; dull pain in head; weariness; light shy

Dizziness; weakness; increased irritation: death

Death'A)

Respiratory disturbances; irritation of eyes;

Serious eye irritation; light shy; palpitation of heart; a few cases of death

Severe pain in eyes and head; dizziness; trembling of extremities; great weakness and deathtA'

500-600

Coughing; collapse and unconsciousnesstA)

600 or greater

Collapse,(A) unconsciousness,'A)death ~~

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Data secured from experiments on dogs that have a susceptibilitysimilar to men.

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