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FAQ: Hydrogen Sulfide Gas (H2S)

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Environment, Great Lakes, and Energy

FAQ: Hydrogen Sulfide Gas (H2S)

Regulation and Jurisdiction of H2S Activities


Activities that do or could produce hydrogen sulfide (H2S) as a result of oil and gas production or exploration, are regulated by the Michigan Department of Environment, Great Lakes, and Energy (EGLE) and the Michigan Public Service Commission (MPSC) as follows:

The Oil, Gas, and Minerals Division (OGMD) of the EGLE regulates the drilling, production and transportation through flow lines from the well to surface facilities.

The Air Quality Division (AQD) of the EGLE issues permits on some of the equipment associated with wells and processing facilities such as storage tanks, flares and other fuel burning equipment, depending on the amount of emissions expected to be discharged.

The Michigan Public Service Commission (MPSC) regulates common carrier pipelines which transport gas and oil from several wells of diverse ownership.

  • Hydrogen Sulfide is a colorless, transparent gas with a characteristic of a rotten-egg odor at low concentrations and not detectable by odor at high concentrations.

    Chemical symbol: H2S

    Specific Gravity: 1.192 (heavier than air)

    Explosive limits: Lower: 4% , Upper: 44% volume in air

    Ignition Temperature: 500° F

    Solubility in water: 2.9 volumes of gas , per volume of water at 20° C

  • This information excerpted from the American National Standards Institute standard: Z37.2-1972 Acceptable Concentrations of Hydrogen Sulfide.

    Hydrogen Sulfide is an extremely toxic and irritating gas. Free hydrogen sulfide in the blood reduces its oxygen-carrying capacity, thereby depressing the nervous system. Hydrogen sulfide is oxidized quite rapidly to sulfates in the body, therefore no permanent aftereffects occur in cases of recovery from acute exposures unless oxygen deprivation of the nervous system is prolonged. There is no evidence that repeated exposures to hydrogen sulfide result in accumulative or systemic poisoning. Effects such as eye irritation, respiratory tract irritation, slow pulse rate, lassitude, digestive disturbances, and cold sweats may occur but these symptoms disappear in a relatively short time after removal from the exposure.

    Odors become detectable in concentrations as low as .008 parts per million (ppm)
    (California studies) but the sense of smell is lost after 2-15 minutes at 100 ppm.

    Physiological response:

    10 ppm

    Beginning eye irritation

    50-100 ppm

    Slight conjunctivitis and respiratory tract irritation after 1 hour exposure

    100 ppm

    Coughing, eye irritation, loss of sense of smell after 2-15 minutes. Altered respiration, pain in the eyes and drowsiness after 15-30 minutes followed by throat irritation after 1 hour. Several hours exposure results in gradual increase in severity of these symptoms and death may occur within the next 48 hours.

    200-300 ppm

    Marked conjunctivitis and respiratory tract irritation after 1 hour of exposure

    500-700 ppm

    Loss of consciousness and possibly death in 30 minutes to 1 hour.

    700-1000 ppm

    Rapid unconsciousness, cessation of respiration and death.

    1000-2000 ppm

    Unconsciousness at once, with early cessation of respiration and death in a few minutes. Death may occur even if individual is removed to fresh air at once.

    To avoid discomfort, the (8 hour) time weighted average concentration of hydrogen sulfide shall not exceed 10 ppm.

  • Hydrogen Sulfide is a naturally occurring gas mixed with natural gas or dissolved in the oil or brine and released upon exposure to atmospheric conditions. Of the 10,652 producible oil wells in Michigan; 1,360 wells had H2S levels exceeding 300 ppm.

  • Permits are reviewed for the probability of encountering H2S gas based on knowledge of the rock formations from other wells.

    Wells may be no closer than 300 feet to existing occupied structures or public recreation areas.

    Surface facilities (vessels for treating and storage of oil and gas, with associated piping and flares) must be at least 600 feet from existing occupied structures or public recreation areas.

    When a well contains 300 ppm or more of hydrogen sulfide, surface facilities or associated flare stacks may not be located in areas which have been zoned residential before January 8, 1993.

    The permittee must under all circumstances notify the local emergency preparedness coordinator, by certified letter not less than 24 hour before commencing to drill an H2S well.

    Prior to issuance of the permit to drill and operate, a contingency plan must be prepared by the applicant which provides an organized plan of action for alerting and protecting personnel at an H2S well site and the public. This plan identifies:

    • Circumstances that activate the plan.
    • Initial procedures to be followed to account for all staff, restrict access and notify the general public, public authorities and safety agencies.
    • Procedures for evacuating the public.
    • Procedures for burning any gas released from the well.
    • A map showing within 1300 feet of the well the following information:
      • All occupied structures, public recreation areas, roads and railroads
      • Names, telephone numbers and address for residents, businesses, schools, churches, hospitals, offices and public camping or gathering areas.
      • Emergency telephone numbers including permittee, drilling contractor, emergency preparedness coordinator, ambulance, hospital, fire department, EGLE Staff, and the Pollution Emergency Alert System (PEAS).
  • The following safety features are required:

    • The drilling rig must contain wind direction indicators, hydrogen sulfide detection monitors (with an audible alarm at 20 ppm), emergency escape breathing apparatus.
    • All free gas separated from the drilling fluid must be flared and tested for H2S.
    • Proper drilling fluids must be used to prevent formation fluids or gases from escaping from the well.
    • Blowout preventers must be in place and tested, and be capable of immediately closing in the well even if drilling pipe is in the well.
    • Multiple, concentric strings of casing must be cemented in place to protect fresh waters and confine fluids or gases to within the well bore.
  • The following safety features are required: 

    • Warning signs must be posted at the well and markers placed along the flow line.
    • Any vents to the atmosphere must be at least 10 feet above the tank top or 20 feet above the ground. Venting may be prohibited if it results in a verified chronic nuisance odor. When storage vessels release more than 5000 cubic feet of vapors in 24 hours, they must be equipped to convey those gasses to an incinerator, flare or vapor recovery system, the site must be fenced and warning signs posted. Emergency relief valves on these wells must be routed to an incinerator or flare.
    • Incinerators or flares must be designed and equipped to prevent the release of unburned gas to the atmosphere.
    • Wells which produce unattended with pressures greater than 100 psig must be equipped with high-low pressure shut-in systems.
    • Vapor return lines are required on truck loading facilities.
    • All flow lines to first point of sale are required to be marked to denote the presence of a buried line containing hydrogen sulfide, the owner's name and emergency number.
    • Flow lines or facility piping for wells permitted after Sept. 20, 1996 are to be pressure tested every twelve months or visually inspected every three months.
    • Above ground lines are to be protected from accidental damage.
    • OGMD staff inspect production facilities two to four times per year. Facilities known to have a history of problems are inspected more frequently.
  • The same safety equipment as required for drilling, must be installed whenever servicing requires removing the seal on the innermost well casing.

    A revised contingency plan may be required. Field staff can require updating of contingency plans whenever significant changes are noted or a significant action such as well servicing is proposed.

    We have recently issued a clarification to the existing rules which requires all gas produced or discharged during any servicing operation is flared or otherwise properly controlled. 

  • A permittee of a well is required by law to ensure that all employees, including drilling contractors or other independent contractors, who are involved in drilling, completing, testing, producing, repair, workover or servicing on an H2S well have been trained regarding:

    • The properties and effects of H2S.
    • Effects of H2S on materials.
    • Emergency escape procedures.
    • Location and use of safety equipment, briefing areas, detection and warning systems.
    • Corrective actions, shut-in procedures, well ignition procedures and how to notify off-site public authorities identified in the contingency plan.
  • Never enter an area to see where the smell is coming from or to rescue downed personnel. H2S is extremely toxic in high concentrations.

    Notify personnel who can address the problem as follows.


    • If the problem appears that it may be more than just odors such as burning in your eyes or nose, immediately contact your local 911, fire or police department. Move away from any well or facilities near you by going perpendicular to the wind direction.

    Odor complaints:

    • If it appears only to be an odor problem, either notify the company at the number posted on the well sign, the appropriate EGLE OGMD Area Geologist or the Pollution Emergency Alert System (PEAS) at telephone 800-292-4706.
  • Hydrogen Sulfide can be detected by smell at concentrations as low as a few parts per billion. For this reason it is extremely difficult to totally eliminate all odors all the time. Upon receiving complaints, the Supervisor of Wells may require the permittee to calculate the predicted concentration of H2S in the air at the closest occupied structure or public recreation area and may then require appropriate emission control measures.

  • No odor threshold has been legally established in Michigan. The Supervisor of Wells may find, after the permittee has provided calculations and any other testing, that a "nuisance odor" exists. A nuisance odor is defined as an emission of any gas, vapor, fume, or mist, or combination thereof, from a well or its associated surface facilities, in whatever quantities, that causes, either alone or in reaction with other air contaminants, injurious effects to human health or safety; unreasonable injurious effects to animal life, plant life of significant value, or property; or unreasonable interference with the comfortable enjoyment of life or property. Nuisance odors are prohibited and the Supervisor of Wells may take action consistent with the rules to prevent activities causing them or require changes be made to prevent them.

  • Large volumes of gas with high concentrations in sufficient quantities of H2S can be processed to produce elemental sulfur.

  • Low concentrations of H2S can be removed from the gas stream at the well site.

    Low volumes of free gas can be burned.

    The Michigan Public Service Commission has jurisdiction over natural gas production rates and transmission pipelines.

  • Pipeline operators are regulated under the Michigan Gas Safety Code, 1969 PA 165, and its rules to ensure that the public safety is protected to the extent possible in the transportation of gas by pipeline. The statute specifically exempts the gathering of gas in rural locations that lie outside the limits of an incorporated or unincorporated city, town, or village. However, gathering lines located in or occupying the property of schools, hospitals, churches, parks, or similar public places are subject to the code. Also, the commission may define other designated residential or commercial area such as a subdivision, business or shopping center, community development, or similar populated area as a non-rural area subject to the code.

    Natural gas transmission pipelines are regulated under Act 9 of Public Acts of 1929, and require the issuance of a Certificate of Public Convenience and Necessity by the Commission prior to construction. However, there are certain circumstances where pipelines are exempt from Commission jurisdiction. If the pipeline is a common carrier (transporting gas from two or more owners), the Commission also has jurisdiction over its rates, charges and conditions of service.

    In addition, under this statute, the Public Service Commission has the authority to regulate production rates of natural gas from gas wells through the issuance of Well Connection Permits, Allowable Withdrawal Orders and Proration Orders.

  • The Air Quality Division does not issue permits for wells, but may permit some of the equipment associated with wells. Air Quality regulations prohibit release of harmful quantities of H2S in any instance. All sweetening facilities must be permitted by the Air Quality Division. A "sweetening facility" treats sour gas to remove sulfur compounds from the gas. After the company has been issued a permit, and the plant has been constructed, Air Quality District staff are involved in inspecting the plant to determine compliance with its air use permit. District staff also respond to citizen complains regarding gas sweetening plants.