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Hydrogen Sulfide

H2S sign - La Plata County, CO

  • General information 
  • H2S in the news
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    General Information

    Chemical/Physical Properties

    • Hydrogen sulfide gas is a naturally occuring chemical (chemical formula H2S). 
    • The gas has a characteristic rotten egg odor at low concentrations. About half of the population can smell it at concentrations as low as 8 parts per billion (ppb) in air, and more than 90% can smell it at levels of 50 ppb.  At higher concentrations, hydrogen sulfide rapidly deadens the sense of smell.  For most people, this occurs at approximately 150 ppm. 
    • Hydrogen sulfide is heavier than air, and it often settles in low-lying areas where it can accumulate in concentrations that can injure or kill livestock, wildlife, and human beings. Additionally, hydrogen sulfide has been found to migrate into surface soils and groundwater.

    Sources of H2S

    Hydrogen sulfide occurs naturally in the environment (e.g., in volcanic gases, marshes, swamps, sulfur springs, decaying organic matter). It is produced by living organisms, including human beings, through the digestion and metabolism of sulfur-containing materials. Hydrogen sulfide is also a byproduct of many industrial processes, such as paper manufacturing, sewage treatment, landfills, or concentrated animal feed operations (CAFOs).

    Hydrogen sulfide gas also is found in petroleum and natural gas. Oil or natural gas is considered sour if it has a high percentage of hydrogen sulfide.[1] Natural gas can contain up to 28 percent hydrogen sulfide gas, consequently,  it may be an air pollutant near petroleum refineries and in oil and gas extraction areas. The principal source of anthropogenic hydrogen sulfide is as a by-product in the purification of natural gas and refinement of crude oil.[2]  Atmospheric releases of hydrogen sulfide represent the most significant public health concern for the geothermal energy industry.  

    Sour Gas

    As mentioned above, oil or natural gas is considered sour if it has a high percentage of hydrogen sulfide. It has been estimated that 15 to 25% of natural gas in the U.S. may contain hydrogen sulfide.[3]  Worldwide, the percentage could be as high as 30%. It has been reported, as well, that new drilling is increasingly being focused on deep gas formations that tend to be sour.[4]  Although the exact number of sour wells are not available, the EPA has reported that in the U.S. "the potential for routine H2S emissions [at oil and gas wells] is significant." [5]

    Releases of hydrogen sulfide from sour gas wells or facilities may occur in a number of ways.  U.S. EPA has collected documentation of sour gas well blowouts, line releases, extinguished flares, collection of sour gas in low-lying areas, and leakage from idle or abandoned wells that have impacted the public near oil and gas extraction sites.[6]  Other possible sources of hydrogen sulfide emissions at sour oil and gas operations are gas venting, and fugitive emissions (leaks) from well head equipment and compressors.

    Environmental Concentrations of H2S

    Typically, areas that are not exposed to industrial releases of hydrogen sulfide have airborne concentrations of less than 1 part per billion (ppb) hydrogen sulfide.  Some non-industrial areas, however, do have higher ambient levels than 1 ppb, because hydrogen sulfide is a natural byproduct of decomposing organic matter than contains sulfur.  For example, Cooper reported short-term hydrogen sulfide levels as high as 62 ppb in Florida wetlands.[7]

    In areas with industrial sources of hydrogen sulfide, average concentrations of hydrogen sulfide in nearby neighborhoods may be present in the low parts per billion range, although maximum concentrations can be in the 100s of parts per billion range or higher (e.g., if there has been a large, industrial release).  Also, spills, leaks, malfunctions or build-up of hydrogen sulfide in enclosed or low-lying areas can result in much higher, and sometimes lethal levels.

    Examples of concentrations of hydrogen sulfide in communities with industrial activities:

    • South Karelia, Finland: An air pollution study in the neighborhood of a pulp mill reported an average level of 3 ppb hydrogen sulfide, with a maximum 4-hour measurement of 40 ppb.
    • In a neighborhood study near an oil refinery, peak measurements of 10 and 100 ppb were reported. 
    • Odessa, Texas: Residents living close to an industrial wastewater facility were exposed to levels ranging from 7-500 ppb.

    H2S air monitoring in oil and gas communities

    When oil and gas wells and facilities are situated near residential areas, there is the possibility that residents will be routinely exposed to hydrogen sulfide.

    State agencies from across the United States receive hydrogen sulfide related complaints from citizens. In 2006, Lana Skrtic, a Masters degree student at the University of California at Berkeley, collected information on state studies conducted in response to hydrogen sulfide complaints related to oil and gas operations in Arkansas, Louisiana, New Mexico, and North Dakota. Download the Skrtic report.  The table below summarizes the hydrogen sulfide concentrations measured in the four studies.

    Briefly, these studies revealed that:

      H2S sampling in four oil and gas communities

      Hydrogen sulfide sampling in four oil and gas communities. (click here for a larger version of the chart)

    •  hydrogen sulfide is present at or near oil and gas facilities, including oil and gas wells, tank batteries, gas processing plants, flares, compressor stations and refineries. 
    • levels of hydrogen sulfide ranged from the relatively low concentration of 2 ppb (recorded in Louisiana) to concentrations in the 1,000 ppb range (observed in New Mexico).  Even the lowest average hydrogen sulfide concentration at these sites was higher than normal urban background levels, which are typically less than 1 ppb.  
    • As reported by Skrtic, "The levels measured in this study may be expected to produce a persistent odor, which has been shown in one study to have a negative effect on the mood of nearby residents."

    In August, 2005, Wilma Subra and the Oil and Gas Accountability Project spent five days in Monroe, Conecuh and Escambia counties in Alabama. The purpose of the visit was to measure concentrations of hydrogen sulfide and volatile organic compounds (VOCs) in the vicinity of known sources of air emissions, and to measure ambient concentrations of hydrogen sulfide and VOCs in residential neighborhoods. The goal of the project was not to identify facilities that have been breaking air quality laws, but rather, to determine if there is a potential air pollution problem that needs to be investigated and addressed in order to protect the health of the citizens in these Alabama counties.

    As reported in the OGAP report, Air Sampling Conducted in Monroe, Conecuh and Escambia Counties, Alabama, hydrogen sulfide levels sampled in residential areas were measured at concentrations in the 100s and 1,000s of parts per billion. This is significantly elevated compared to normal urban background levelsof less than 1 ppb, but comparable to other oil and gas regions in the U.S., where levels of hydrogen sulfide have been measured in the 100-15,000 ppb range in the vicinity of wells and facilities.

    Based on the findings for both hydrogen sulfide and VOCs (which were in the parts per million range), it was recommended to the Alabama Department of Environmental Management that follow-up air monitoring occur both in residential and oil and gas production areas. The monitoring would help to hone-in on operations that may be emitting large quantities of hydrogen sulfide and VOCs, and evaluate whether the concentrations in residential neighborhoods are posing a threat to human health and the environment.

    Health Effects from H2S Exposure

    Common symptoms of exposure to long-term, low levels of hydrogen sulfide include headache, skin complications, respiratory and mucous membrane irritation, respiratory soft tissue damage and degeneration, confusion, impairment of verbal recall, memory loss, and prolonged reaction time. Exposure to high concentrations can cause unconsciousness, known as "knockdown," and can be lethal.

    The following information on health effects related to exposure to hydrogen sulfide was excerpted from Section 3.1.3 of the OGAP Report Air Sampling Conducted in Monroe, Conecuh and Escambia Counties, Alabama.  Please download the report to find the references for the information below.

    Exposure to hydrogen sulfide is one of the leading causes of sudden death in the workplace.   At concentrations greater than 500 parts per million, inhalation of hydrogen sulfide can lead to immediate collapse and unconsciousness.  A single breath at 1,000 ppm results in immediate loss of consciousness, cardiac arrest and death unless the unconscious victim is successfully revived.  Unconsciousness and death have occurred in situations of prolonged exposure to hydrogen sulfide at concentrations of 50 ppm.  Many occupational and community studies have documented the adverse health effects of exposure to relatively high levels of H2S.

    Almost all organ systems are affected by hydrogen sulfide, but the most susceptible are those with exposed mucous membranes (e.g., eyes,  noise and throat) and those with high oxygen demands (e.g., lungs, brain). Neurotoxicity of the central nervous system (causing nausea, dizziness, confusion, headaches and sleeping problems) and pulmonary edema (build-up of fluid in the lungs) are other well-documented effects of hydrogen sulfide poisoning. Cardiovascular and gastrointestinal toxicity are also associated with H2S exposure.

    Research conducted by Kaye Kilburn, a medical doctor and professor of medicine at the University of Southern California, suggests that exposure to hydrogen sulfide may cause long-term, irreversible human health effects. Kilburn performed physiologic and psychological measurements on nineteen exposed individuals, and compared results with 202 unexposed subjects.  Of the 19 exposed subjects, 10 were exposed at work sites, which included four oil and gas operations, and nine were exposed in their residences, which were near various sources of hydrogen sulfide. The concentrations to which the subjects were exposed are not known. Kilburn found that depression, anger, fatigue, tension, confusion and respiratory ailments were significantly higher in exposed subjects than the control group. 

    Increasingly, scientific research is revealing that even low concentrations of hydrogen sulfide (in the low parts per million or even the parts per billion range) can affect human health, especially when exposure occurs over an extended period of time. For example, data collected in a study of sewer workers indicated that low-level exposure to hydrogen sulfide may be associated with reduced lung function.  

    The following studies provide more information on the potential association between low-level exposures to hydrogen sulfide and health effects.

    • A study of hydrogen sulfide in the workplace found that workers complained of eye pain at a level of 6.4 ppm. 
    • Clinical studies suggest that short-term exposure to hydrogen sulfide at concentrations of 2 ppm may induce bronchial obstruction. In a study investigating the effects of hydrogen sulfide on asthmatics, two out of ten subjects exhibited a pronounced response when exposed to 2 ppm hydrogen sulfide. Airway resistance and conductivity were affected by more than 30%, suggesting significant bronchial obstruction.
       
    • Former workers and residents living downwind of a crude oil processing plant had neurophysiological abnormalities.  Residents in this study were exposed to hydrogen sulfide at 10 ppb, although concentrations occasionally reached 100 ppb. 
    • Residents near pulp and paper mills in Finland have reported an excess of health symptoms compared to residents living in a community without any industrial hydrogen sulfide sources. The annual mean concentrations of hydrogen sulfide in the affected community was 8 µg/m3 (5.7 ppb). Symptoms included respiratory, eye and nasal problems).  Residents in the pulp and paper community were also exposed to other sulfur compounds, but hydrogen sulfide accounted for more than two-thirds of the sulfur compounds monitored in the community.
        
    • Symptoms of adverse health effects experienced by residents in Odessa, TX and Puna, Hawaii, two communities with industrial sources of hydrogen sulfide were compared to the same symptoms in three communities without industrial sources of hydrogen sulfide. The residents in Odessa were exposed to hydrogen sulfide concentrations of 7-27 ppb (annual average), with maximum 8-hour measurements between 335 and 503 ppb.  Exposure in Puna is less clear, but some data from the 1990s indicate hourly averages in the low-ppb range, with most below 1 ppb.  Between June 1996 and 1997, peak hydrogen sulfide concentrations was 301.7 ppb.  In other years, releases of hydrogen sulfide between 200-500 ppb were reported.  The two hydrogen sulfide-exposed communities were similar with respect to the adverse health effects (e.g., central nervous systems, ear/nose/throat, respiratory, muscle/bone, skin, immune, cardiovascular, digestive, teeth/gums, urinary, blood) reported by residents.  Percentages of affected residents in the hydrogen sulfide-exposed communities were statistically different (higher) than the non-exposed communities.

    H2S Regulations

    There are no international health-based standards for hydrogen sulfide. The World Health Organization (WHO) has an air quality guideline of 150 µg/m3 (10.6 ppb) hydrogen sulfide, averaged over a 24-hour period.  This guideline is based on the avoidance of eye irritation.  Also, WHO recommends that hydrogen sulfide concentrations not exceed 0.005 ppm (5 ppb; 7 µg/m3), over a 30-minute period, to avoid substantial complaints about odor.

    Within the United States, there is no federal ambient air quality standard for hydrogen sulfide, but more than 30 states have chosen to independently regulate hydrogen sulfide levels to protect the public from adverse effects related to hydrogen sulfide exposure. Some states have standards based on short-term hydrogen sulfide levels (averaged over 15 minutes), while others use an average over a much longer period of time (extending up to one-year).  The table, below,  includes information for states that have ambient air quality standards (or guidelines) for hydrogen sulfide.

    The most stringent one-hour standard - found in New Mexico, New York and Kentucky - is 10 parts per billion (ppb).  In other words, those states believe there will be some effect on citizens exposed to hydrogen sulfide at a level of 10 ppb for at least one hour.  The effects may be health-related or the odors may create a nuisance for the citizens.

    At least twelve states have standards for hydrogen sulfide measured over a 24-hour period.  These levels are lower than the 1-hour limits, and vary from concentrations of 0.65 ppb (Massachusetts) to 200 ppb (Oklahoma).


    H2S In the News

     

    Rural family loses sour gas battle because court won't force regulator to review wells (Calgary Herald, March 27, 2008, Joel Kom)

    A southern Alberta family has lost its battle to force the provincial energy regulator to reconsider two sour gas wells in light of the family's health, which it maintains has deteriorated because of nearby wells.

    In a provincial Court of Appeal judgment released Wednesday, three justices ruled the Energy and Utilities Board -- which has since been divided into two branches -- did nothing wrong in how it handled the case of the Graff family near Vulcan, about 120 kilometres southeast of Calgary.

    The case hinged on medical evidence the Graffs said showed the wells, drilled by EnCana Corp. near the family's home after the company won approval in 2006 and 2007, were cumulatively damaging their health.

    The Graffs claim the regulator didn't do enough to consider the evidence, while the regulator's lawyers argued the family didn't follow the proper paths available to them to file the documents.

    The court sided with the regulator, saying the Graffs didn't do enough to make sure the medical claims were put before the then-EUB and that it wasn't unreasonable for the regulator to ask for proof of damaged health.

    Jim Hope-Ross, the lawyer for Barbara and Larry Graff and their adult son, Darrell, said he found it "disturbing" that the court considered the Graffs "the authors of their own demise."

    "If it's something cumulative, as it is with the Graffs, how can you ever establish that?" he said. "It puts an awfully tough onus on the little guy."

    The Graffs didn't want to publicize their health problems, he added, and the regulator could have done more to consider their request for privacy.

    But Bob Curran, a spokesman for the Energy Resources Conservation Board, which now handles the oil and gas regulation formerly overseen by the EUB, said anything filed with the regulator has to be made public.

    When the family asked for it to be kept private, but didn't file a confidentiality request, that left the regulator to choose protecting the family's privacy over keeping the documents -- leading to staff returning the evidence so that it wasn't part of the case.

    "Our hands were tied at that point," he said. "We were put in an untenable position."

    Curran said the appeal court's ruling showed the regulator has an appropriate process for people to show their concerns.

    Wednesday's decision was mostly rendered moot, however, after EnCana decided to abandon the wells because they weren't producing much gas.

    EnCana spokesman Alan Boras said the wells were "test wells," adding the court ruling showed EnCana nevertheless did what was asked of it.

    Sour gas leak kills worker:  Employee never returned from changing flow meter at remote gas facility (The Edmonton Journal, March 8, 2008, Jennifer Fong).[8]

    Edmonton - The death of an oilfield operative from sour gas exposure near Fox Creek has triggered an investigation by police, safety and industry regulatory officials.

    The a 46-year-old employee of ELH Enterprises in Whitecourt was working on contract for Calgary-based oil and gas company Orleans Energy when he died on the job Friday afternoon.  Colin MacPhail, speaking for Alberta's workplace health and safety program, said the long-time oilpatch worker was working alone, changing a gas-flow measuring device inside Orleans' Kaybob inlet separator gas facility. The facility is in a remote, wooded area 45 kilometres west of Fox Creek in northwestern Alberta.  There were high levels of hydrogen sulphide (H2S) present, said RCMP Fox Creek division Const. Dean Purcka.

    Orleans Energy president and CEO Barry Olson said in a statement the man was "performing routine operations within the facility."  When the oilfield worker failed to check in at 5 p.m., another man was sent to check on him, said MacPhail, who is with Alberta Employment, Immigration and Industry. Upon arrival, he found that the hydrogen sulphide alarm system had been set off.

    The operative was pronounced dead at the scene.

    The oilsands site, leased by Orleans, has been voluntarily shut down.  ELH Enterprises declined to comment.

    Health Concerns May Spur Hydrogen Sulfide Ruling ( Wall Street Journal, Ilan Brat  Thursday,December 13, 2007)


    The U.S. Environmental Protection Agency is considering broadly regulating hydrogen sulfide, a common gas that smells like rotten eggs and has been increasingly linked to a variety of health problems for people living and working near petroleum, confined livestock, paper and landfill operations.
     
    Hydrogen sulfide has long been known to be deadly in high concentrations. However, growing scientific evidence shows the gas may also have health effects at low levels.
     
    The agency is "reviewing existing scientific information to determine whether a listing is justified, and we are conducting our own studies in order to fill data gaps - so that ultimately, we will be able to make a determination," Alison Davis, a spokeswoman for the EPA's Office of Air Quality Planning and Standards, said in an email statement.
     
    The potential new rule, likely to face stiff opposition from industry, comes at a time when soaring energy prices have encouraged the U.S. energy industry to drill deeper in order to explore hard-to-reach reservoirs - operations that can bring increased hydrogen sulfide emissions. At the same time, health complaints have multiplied in recent years from people living near dumps specializing in construction and demolition debris. These sites have mushroomed in the wake of the national housing boom and a series of devastating Gulf Coast hurricanes.
     
    Hydrogen sulfide is produced when organic material containing sulfur decomposes. It can also be produced from chemical reactions. The gas is readily found in the Earth's crust and in extremely low levels in the atmosphere. In dumps specializing in construction and demolition debris it can be produced when gypsum decomposes.
     
    The gas was once thought to be relatively harmless in low concentrations. Some scientists and federal health investigators say mounting research in recent years shows that prolonged exposure to relatively low levels may affect memory, coordination, eyes and breathing.
     
    However, those researchers caution that more study is needed and note that communities studied are often exposed to several chemical compounds at the same time, clouding the results.

    Family allowed to fight sour gas decision (Calgary Herald, January 24, 2007, Renata D'Aliesio)  

    A southern Alberta family who claims sour gas activity damaged their health has won the right to challenge the provincial energy regulator's approval of a new well near their home.  In a provincial Appeal Court judgment Tuesday, Justice Marina Paperny ruled the Alberta Energy and Utilities Board -- the province's energy watchdog -- made a mistake when deciding to discount the Graff family's concerns because they live outside a consultation zone in the Vulcan area. Tuesday's ruling grants the fourth-generation Alberta family the legal right to appeal last year's approval for EnCana Corp. to drill a sour gas well 100 kilometres southeast of Calgary.

    "We will endeavour to have concerns about our health heard," said 55-year-old Barbara Graff, who alleges previous activities from other gas companies have left her and her adult son extremely sensitive to low levels of chemicals. "At this point we feel our lives are being threatened."

    Alabama residents suspect health problems to be related to hydrogen sulfide and contaminated water from oil and gas drilling (9CBS 8 TV, Montgomery, AL)

    Residents along Old Stage Road in Conecuh County, Alabama, have been experiencing headaches, open sores, miscarriages and other health effects, which they believe are related to air and water contamination.

    In March, 2006, an oil and gas company operating in Conecuh County was fined for releasing unpermitted emissions of various compounds including hydrogen sulfide, a potentially deadly gas often associated with oil production in south Alabama. Residents of Old Stage Road have also noticed thick, unidentified foamy substances in water they say is connected to their water wells.

    The Alabama Department of Environmental Management, while not admitting that contamination of water wells has occurred, has agreed to help get them connected to city water. Sources: Mobile Press Register. March 28, 2006. "ADEM proposed big fine for oil company polluting in Conecuh."


    FOOTNOTES

    [1]  Depending on the jurisdiction, the official definition of sour gas varies.  For example, in Canada, the petroleum industry considers natural gas to be sour if it contains more than 1% hydrogen sulfide.  The U.S. Environmental Protection Agency (EPA) considers natural gas to be "sour" if hydrogen sulfide is present in amounts greater than 5.7 milligrams per normal cubic meters, which is equivalent to 0.25 grains per 100 standard cubic feet.  (Source:  U.S. Environmental Protection Agency. 1995. Petroleum Industry - Compilation of Air Pollutant Emission Factors, Vol. 1, Stationary Point and Area Sources.)

    [2] Chou, S. 2003. Hydrogen Sulfide: Human Health Aspects. Concise International Chemical Assessment Document 53. Prepared for the World Health Organization. p. 6.  

    [3] Dalrymple, D.A., Skinner, F.D. and Meserole, N.P. 1991. Investigation of U.S. Natural Gas Reserve Demographics and Gas Treatment Processes. Topical Report, GRI-91/0019, Section 3.0, pp. 3-1 to 3-13. Gas Research Institute. And Hugman, R.H., Springer, P.S. and Vidas, E.H.  Chemical Composition of Discovered and Undiscovered Natural Gas in the United States: 1993 update. Topical Report, GRI-93/0456. p. 1-3. Gas Research Institute.  In McIntush, K.E., Dalrymple, D.A. and Rueter, C.O. 2001. "New process fills technology gap in removing H2S from gas," World Oil, July, 2001.

    [4] Quinlan, M., 1996. Evaluation of selected emerging sulfur recovery technologies, GRI Gas Tips, 3(1):26-35. In McIntush, K.E., Dalrymple, D.A. and Rueter, C.O. 2001. "New process fills technology gap in removing H2S from gas," World Oil, July, 2001.

    [5] U.S. Environmental Protection Agency. October 1993. Report to Congress on Hydrogen Sulfide Air Emissions Associated with the Extraction of Oil and Natural Gas. EPA-453/R-93-045, p.III-35. 

    [6] U.S. Environmental Protection Agency. October 1993. Report to Congress on Hydrogen Sulfide Air Emissions Associated with the Extraction of Oil and Natural Gas. EPA-453/R-93-045, p.III-38.

    [7] Cooper, W.J.  1987. "Emissions of biogenic sulfur compounds from several wetland soils in Florida." Atmospheric Environment. 21:1491-1495.

    [8] Fox Creek death prompts investigation, Jennifer Fong ,  The Edmonton Journal Published: Saturday, March 08, 2008.

    For More Information

    OGAP Resources

    Other Resources

    • Hydrogen Sulfide, Oil and Gas, and Peoples' Health. (Master's Paper, Lana Skrtic, M.S., University of California at Berkeley)
    • Big Oil in Small Town America is a new book that documents a Michigan community's struggle to get oil and gas companies, and various government agencies charged with protecting citizens, to take responsibility for what the citizens claim were illegal emissions of hydrogen sulfide. Hydrogen sulfide is a toxic by-product of some oil and gas operations. The book's author, Jaime Long, suffered a stroke, which she attributes to oil and gas chemical exposures.
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