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General Safety and Health Hydrogen Sulfide Gas

JSA

Note: It is not the intent of this section to create an H2S contingency plan.

Hydrogen Sulfide or sour gas (H2S) is a flammable, colorless gas that is toxic at extremely low concentrations. It is heavier than air, and may accumulate in low-lying areas. It smells like "rotten eggs" at low concentrations and causes you to quickly lose your sense of smell. Many areas where the gas is found have been identified, but pockets of the gas can occur anywhere. [More]

Iron sulfide is a byproduct of many production operations and may spontaneously combust with air.

Flaring operations associated with H2S production will generate Sulfur Dioxide (S02), another toxic gas.

Active monitoring for hydrogen sulfide gas and good planning and training programs for workers are the best ways to prevent injury and death.

Also see: NIOSH Classification of H2S Hazard Areas.

Hazards may include and/or be related to the following:

Figure 1. Hydrogen sulfide warning sign: Warning Hazardous Area is in yellow letters on a black background. In black letters on a yellow background, the sign says Hydrogen Sulfide, Extreme Health Hazard, Fatal or Harmful if Inhaled.

Figure 1. Hydrogen sulfide warning sign: Warning Hazardous Area is in yellow letters on a black background. In black letters on a yellow background, the sign says Hydrogen Sulfide, Extreme Health Hazard, Fatal or Harmful if Inhaled.

Figure. 2. SCBA

Figure. 2. SCBA

Figure. 3. Gas detector

Figure. 3. Gas detector

All personnel working in an area where concentrations of Hydrogen Sulfide may exceed the 10 Parts Per Million (PPM) should be provided with training before beginning work assignments.

Potential Hazard:

  • H2S exposure greater than the Permissible Exposure Limit (PEL).

Possible Solutions:

Implement an H2S contingency plan (see API) including, but not limited to:

  • Appropriate instruction in the use of hydrogen sulfide safety equipment to all personnel present at all hydrogen sulfide hazard areas.
  • Gas detection where hydrogen sulfide may exist.
  • Appropriate respiratory protection for normal and emergency use. [29 CFR 1910.134]

For emergency response information, see Hazardous Waste and Emergency Response (HAZWOPER) Standard, [29 CFR 1910.120].

Comprehensive training should be provided for workers in H2S operations. Example topics include:

  • Identification of the characteristics, sources, and hazards of Hydrogen Sulfide.
  • Proper use of the Hydrogen Sulfide detection methods used on the site.
  • Recognition of, and proper response to, Hydrogen Sulfide warnings at the workplace.
  • Symptoms of Hydrogen Sulfide exposure.
  • Proper rescue techniques and first-aid procedures to be used in a Hydrogen Sulfide exposure.
  • Proper use and maintenance of personal protective equipment. Demonstrated proficiency in using PPE should be required.
  • Worker awareness and understanding of workplace practices and maintenance procedures to protect personnel from exposure to hydrogen sulfide.
  • Wind direction awareness and routes of egress.
  • Confined space and enclosed facility entry procedures.
  • Locations and use of safety equipment.
  • Locations of safe briefing areas.
  • Use and operation of all Hydrogen Sulfide monitoring systems.
  • Emergency response procedures, corrective action, and shutdown procedures.
  • Effects of Hydrogen Sulfide on the components of the Hydrogen Sulfide handling system.
  • The importance of drilling fluid treating plans prior to encountering Hydrogen Sulfide.

Additional Information:

  • RP 49, Recommended Practice for Drilling and Well Servicing Operations Involving Hydrogen Sulfide. American Petroleum Institute (API), (2001, May/Reaffirmed 2007, March). Includes well drilling, completion, servicing, workover, downhole maintenance, and plug and abandonment procedures conducted with hydrogen sulfide present in the fluids being handled.
  • Safety Issues. Association of Energy Services Companies (AESC).
    • Use of Anchors and Guywires
    • Use of Compressed Gas Cylinders
    • Crane Operation
    • Proper Electrical Safety (including hot sticks)
    • Hot Work
    • Fall Protection Systems
    • H2S - Hydrogen Sulfide
    • Respirator Usage
    • Use of wooden, metal and plastic (fiberglass) portable ladders
    • Scaffolding
    • Vehicle Operation
Fig. 4. H2S metal fatigue

Fig. 4. H2S metal fatigue

Metal fatigue, including hydrogen embrittlement or sulfide stress cracking, can result in a release of hydrogen sulfide gas.

Potential Hazard:

  • Being exposed to Hydrogen Sulfide.
  • Getting Injured due to equipment failure.

Possible Solutions:

  • Select materials in accordance with the MR0175/ISO15156 criteria for H2S service.
    • MR 0175C, Metals for Sulfide Stress Cracking and Stress Corrosion Cracking Resistance in Sour Oilfield Environments. National Association of Corrosion Engineers (NACE), (2003, December) [Also ISO 15156, Petroleum and natural gas industries-Materials for use in H2S containing environments in oil and gas production, International Standards Organization (ISO)].
  • Treat drilling fluids to chemically reduce corrosion failures.

It is possible for hydrogen sulfide gas to accumulate in any low or enclosed area, such as a gas venting system, mud system, cellars, pits, and tanks.

Potential Hazard:

  • Being exposed to Hydrogen Sulfide.

Possible Solutions:

  • Provide adequate ventilation for the removal of any accumulation of H2S.
  • Implement effective confined space entry program.

Additional guidance materials are available from:

  • RP 49, Recommended Practice for Drilling and Well Servicing Operations Involving Hydrogen Sulfide. American Petroleum Institute (API), (2007, March). Includes well drilling, completion, servicing, workover, downhole maintenance, and plug and abandonment procedures conducted with hydrogen sulfide present in the fluids being handled.
    • Spec 6A, Specification for Wellhead and Christmas Tree Equipment (includes Errata 3 dated June 2006). 19th Edition. (2004, July). [Also ISO10423:2003] Specifies requirements and gives recommendations for the performance, dimensional and functional interchangeability, design, materials, testing, inspection, welding, marking, handling, storing, shipment and purchasing, of wellhead and christmas tree equipment for use in the petroleum and natural gas industries.
    • Spec 6A 718, Specification of Nickel Base Alloy 718 (UNS N07718) for Oil and Gas Drilling and Production Equipment (includes Addendum dated March 2006). 1st Edition. (2004, March). Provides specification requirements for Nickel Base Alloy 718 (UNS N07718) that are intended to supplement the existing requirements of API Spec 6A and ISO 10423. These additional specification requirements include detailed process control requirements and detailed testing requirements.
    • For additional information, see the API website.
  • Safety Issues. Association of Energy Services Companies (AESC).
    • Use of Anchors and Guywires
    • Use of Compressed Gas Cylinders
    • Crane Operation
    • Proper Electrical Safety (including hot sticks)
    • Hot Work
    • Fall Protection Systems
    • H2S - Hydrogen Sulfide
    • Respirator Usage
    • Use of wooden, metal and plastic (fiberglass) portable ladders.
    • Scaffolding
    • Vehicle Operation
  • MR 0175, Metals for Sulfide Stress Cracking and Stress Corrosion Cracking Resistance in Sour Oilfield Environments. National Association of Corrosion Engineers (NACE), (2003, December) [Also ISO 15156, Petroleum and natural gas industries—Materials for use in H2S containing environments in oil and gas production, International Standards Organization (ISO)].
  • Accident Prevention Guide. International Association of Drilling Contractors (IADC).
  • Respiratory protection as it relates to oil fields. OSHA Standard Interpretation, (1993, April 14).
  • 29 CFR 1910.134, Respiratory protection. OSHA Standard.
  • NFPA 70, National Electrical Code. National Fire Protection Agency (NFPA), (2014).
  • International Association of Drilling Contractors (IADC)
    • IADC H2S Safety Handbook
    • IADC H2S Safety for Oil, Gas & Petrochemical Industry
    • IADC H2S Safety in Drilling and Production
    • IADC Oilfield H2S Safety Training

State Programs

Training Programs

  • Drilling Technology Series. Petroleum Extension Service (PETEX), University of Texas at Austin.
    • Unit I: The Rig and Its Maintenance
    • Unit II: Normal Drilling Operations
    • Unit III: Non-routine Operations
    • Unit IV: Man Management and Rig Management
  • ASC Z390.1, Accepted Practices for Hydrogen Sulfide Safety Training Programs. American Society of Safety Engineers (ASSE), (2006, June).

H2S Training and Information Links

A.1 Physical Data

  • Chemical Name: Hydrogen Sulfide
  • CAS Number: 7783-06-4
  • Synonyms: Sulfureted hydrogen, hydrosulfuric acid, dihydrogen sulfide
  • Chemical Family: Inorganic sulfide
  • Chemical Formula: H2S
  • Normal Physical State: Colorless gas, slightly heavier than air. Vapor density (specific gravity) at 59°F (15°C) and 1 atmosphere = 1.189.
  • Auto ignition Temperature: 500º F
  • Boiling Point: -76º F
  • Melting Point: -117.2º F
  • Flammable Limits: 4.3-46 percent vapor by volume in air
  • Solubility: Soluble in water and oil: solubility decreases as the fluid temperature increases
  • Combustibility: Burns with a blue flame to produce sulfur dioxide (SO2). Refer to Appendix B Odor and Warning Properties: Hydrogen sulfide has an extremely unpleasant odor, characteristic of rotten eggs, and is easily detected at low concentrations: however, due to rapid onset of olfactory fatigue and paralysis (inability to smell) ODOR SHALL NOT BE USED AS A WARNING MEASURE.

A.2 Exposure Limits

The American Conference of Governmental Industrial Hygienists recommends a Threshold Limit Value of 1 ppm and a short-term exposure (STEL) limit of 5 ppm averaged over 15 minutes. Exposure at the STEL should not be repeated more than four times per day with at least 60 minutes between successive exposures in this range.

A.3 Physiological Effects

Inhalation at certain concentrations can lead to injury of death. The 300 ppm is considered by the ACGIH as Immediately Dangerous to Life and Health. Hydrogen sulfide is an extremely toxic, flammable gas that may be encountered in the production of gas well gas, high-sulfide, high sulfur content crude oil, crude oil fractions, associated gas, and waters. Since hydrogen sulfide is heavier than air, it can collect in low places. It is colorless and has a foul rotten egg odor. In low concentrations, H2S sometimes can be detectable by its characteristic odor; however, the smell cannot be relied upon to forewarn of dangerous concentrations (greater than 100ppm) of the gas because it rapidly paralyzes the sense of smell due to paralysis of the olfactory nerve. A longer exposure to the lower concentrations has a similar desensitizing effect on the sense of smell.

It should be well understood that the sense of smell will be rendered ineffective by hydrogen sulfide, which can result in an individual failing to recognize the presence of dangerously high concentrations. Exposure to hydrogen sulfide causes death by poisoning the respiratory system at the cellular level. Symptoms from repeated exposures to low concentrations usually disappear after not being exposed for a period of time. Repeated exposures to low concentrations that do not produce effects eventually may lead to irritation if the exposures are frequent.

A.4 Respiratory Protection

Respiratory protection shall be worn above the action level. Refer to 6.6 for proper breathing equipment recommendations for oil and gas well drilling and servicing operations involving hydrogen sulfide.

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