**Snapshot: In the United States, hydrogen sulfide exposure is mostly regulated as an occupational hazard, with some environmental regulations for controlling emissions from major sources.**
## Environmental regulations
Hydrogen sulfide is flammable gas that is both a nuisance at low concentrations and a toxin at higher concentrations or long exposures. Possibly due to it’s fairly rapid oxidation in the atmosphere (from 1 to 42 days; ASTDR, 2016), the United States currently has no ambient air quality standards for hydrogen sulfide; it is not included as a regulated criteria or hazardous air pollutant.
With the 1990 amendments to the Clean Air Act, [section 112(n)(5)](https://www3.epa.gov/ttn/atw/112n/112npg.html) requested a study of hydrogen sulfide emissions associated with oil and gas extraction. The results of that study can be found in “Hydrogen Sulfide Air Emissions Associated with the Extraction of Oil and Natural Gas” (EPA-453/R-93-045; NTIS publication # PB94-131224). This study did not lead to ambient air quality standards for hydrogen sulfide nor its listing as a hazardous air pollutant.
Hydrogen sulfide is regulated with regards to accidental release, as per Clean Air Act section 112(r). The [Risk Management Plan Rule (RMP)](https://www.epa.gov/rmp/risk-management-plan-rmp-rule-overview) implements this part of the Clean Air Act by requiring that any facility that houses a significant quantity of a hazardous chemical develop a risk management plan to reduce the likelihood of chemical spills and accidents, and appropriately respond to accidents. The threshold quantity of hydrogen sulfide over which a site is subject to the RMP rule is 10,000 lbs. Effectively, this means that industries that use hydrogen sulfide, such as sulfur-producing metallurgy or certain types of oil refineries that use hydrogen sulfide as an additive, will need a risk management plan in place, but that industries where hydrogen sulfide is a byproduct, such as pulping or concentrated agricultural feeding operations (CAFOs) often will not need to make a hydrogen sulfide risk management plan. _Please note that amendments to improve the RMP rule were passed requested by executive order in 2013 after several hazardous spill events, and finalized in January 2017. However, after receiving petitions from chemical industry representatives, the Pruitt Administration of the EPA has stayed implementation of the amendments, and will reconsider them in February 2019. More information can be found [here](https://www.epa.gov/rmp/final-amendments-risk-management-program-rmp-rule)._
## Federal emissions regulations
Hydrogen sulfide is included as a pollutant with restricted emissions on the basis of “Prevention of Significant Deterioration” (PSD). PSD reviews and permitting were established to maintain good air quality and ensure that new major industrial sources and modifications of others don’t impact an area such that the area would be in jeopardy of not meeting the National Ambient Air Quality Standards (NAAQS). Since hydrogen sulfide can oxidize in the atmosphere to sulfur dioxide, which is a criteria pollutant included in the NAAQS, industrial operations who emit hydrogen sulfide above a certain threshold, called a Significant Emissions Rate (SER), will have to obtain a PSD permit. The SER for hydrogen sulfide is 10 tons per year.
## State emissions and ambient air regulations
States have the authority to enact stricter environmental standards than federal standards; federal standards are the minimum that all states must meet. As may be expected, there are a wide variety of environmental standards at the state level, as is the case with regards to hydrogen sulfide. Here we have compiled information about a handful of states’ hydrogen sulfide environmental regulations. Please edit this wiki to add information for more states!
In Colorado, hydrogen sulfide is considered a “criteria” pollutant, which is effectively a classification of a regulated pollutant that is not listed as a hazardous air pollutant, whose emissions are limited and has associated emissions fees. For hydrogen sulfide, a company must provide an Air Pollutant Emissions Notice (APEN) and seek a permit if they emit more than 2 tons of hydrogen sulfide (including direct and fugitive emissions) per year. A table of emissions thresholds for criteria pollutants in Colorado can be found at: https://www.colorado.gov/pacific/cdphe/apen-and-permit-threshold-table.
Since hydrogen sulfide is an odorous pollutant, its emissions have been discussed by the Colorado Air Quality Control Commission with regards to odor regulations. However, as noted in [this document](https://www.colorado.gov/pacific/sites/default/files/5-CCR-1001-4.pdf), the Commission decided not to require hydrogen sulfide APENs for operations subject to odor control regulations, based on expecting annual emissions of 2 to 8 tons and the expense of the Jerome meter for hydrogen sulfide monitoring.
For oil and gas wells that are drilled in high-sulfide rock formations, the operator must file a plan with the Colorado Oil and Gas Conservation Committee that includes public notification and hazard mitigation procedures upon accidental gas release (pursuant to the Bureau of Land Management’s [Onshore Order #6](https://www.blm.gov/nhp/300/wo310/library/ordersntl/order6-linked.html)).
Colorado does not have ambient air standards for hydrogen sulfide.
Michigan does not have additional hydrogen sulfide rules beyond the federal environmental regulations, except with regards to hydrogen sulfide management plans for oil and gas operations (see Part 11 of the Oil and Gas Operations rules: http://w3.lara.state.mi.us/orr/Files/AdminCode/1693_2017-017EQ_AdminCode.pdf). The Michigan Department of Environmental Quality issues permits for some industrial operations that have hydrogen sulfide implications, such as “sweetening facilities” that remove sulfur compounds from natural gas (see [general info about H2S in MI regulations here](http://www.michigan.gov/deq/0,4561,7-135-3311_4231-9162--,00.html). If there are complaints about nuisance odors, and the permittee operating a natural gas well site tests or shows calculations that demonstrate there could be a hydrogen sulfide or other odorous emission, then the Michigan Supervisor of Wells can require operational changes to mitigate that odor release. Interestingly, the qualifications for nuisance odors are high and subjective, including causing injury to human health of safety, or “unreasonable” injury to animal life or plant life of “significant value.” See the full description of nuisance odor definition in the H2S information linked earlier in this paragraph.
Minnesota is one of the few states that do have ambient air quality standards for hydrogen sulfide. The official standards can be found on the Minnesota government website [here](https://www.revisor.mn.gov/rules/?id=7009.0080). The hydrogen sulfide limits in ambient air are 0.03 parts per million (ppm), as measured in a 30 minute time-weighted-average sample, which cannot be exceeded more than twice in five consecutive days. Beyond that, 0.05 ppm hydrogen sulfide cannot be exceeded more than twice per year. Please note that 0.05 ppm is equal to 50 ppb (parts per billion).
Pennsylvania also has ambient air quality standards for hydrogen sulfide, listed [here](http://www.dep.pa.gov/Business/Air/BAQ/PollutantTopics/Pages/Ambient-Standards.aspx). Rather than detailing limits with allowable annual exceedances, Pennsylvania maintains a daily and hourly standard that are not to be exceeded. The 24-hour time weighted average limit for hydrogen sulfide is 0.005 ppm (5 ppb), and the 1-hour limit is 0.1 ppm (100 ppb).
Texas has air quality standards for hydrogen sulfide downwind of oil and gas operations. The comprehensive rules are included in [this document](https://www.tceq.texas.gov/assets/public/legal/rules/rules/pdflib/112%60.pdf) dealing with airborne sulfur compounds, and note that the rule for hydrogen sulfide became effective in 1974. It is not clear what means are used to enforce these rules. Sections 112.31 and 112.32 in the linked document state that operations cannot emit hydrogen sulfide to such an extent that downwind properties exceed 0.08 ppm (80 ppb) hydrogen sulfide for more than 30 minutes if people are likely to be present (e.g. commercial or residential), or 0.12 ppm (120 ppb) if there are not usually people there, such as range land.
As a state with significant oil and gas extraction and processing, Texas does recognize the hazardous nature of hydrogen sulfide. In 2012, the rail road commission published a booklet on hydrogen sulfide safety with respect to drilling, production, and transportation, found [here](http://www.rrc.state.tx.us/media/2948/swr36.pdf). Like other states, Texas has adopted the federal emissions limit of 10 tons per year for Prevention of Significant Deterioration from major sources.
Wisconsin does not have ambient air quality standards for hydrogen sulfide, but does have hydrogen sulfide emissions limits. Like other states, Wisconsin has adopted the federal standards of a Significant Emission Rate of 10 tons per year of hydrogen sulfide to require a Prevention of Significant Deterioration review and permit (as detailed in Wisconsin administrative code NR 405.02(27)(a)11). In addition to this annual limit, Wisconsin has two specific emissions limits for hydrogen sulfide. For new stationary sources (e.g. an industrial plant), operations with hydrogen sulfide emissions are required to install continuous monitoring systems, and report the data every six months. Hydrogen sulfide emissions are not allowed to exceed 230 mg/dscm (as detailed [here](https://docs.legis.wisconsin.gov/code/admin_code/nr/400/440/II/26/6/e/3/b)), which is equal to ~165 ppm hydrogen sulfide. For combustion processes that are not followed by incineration, the hydrogen sulfide emissions limit is 10 ppm (as detailed [here](https://docs.legis.wisconsin.gov/document/administrativecode/NR%20440.26(5)(a)2.b)).
# Occupational exposure regulations
The Occupational Safety and Health Administration (OSHA) is part of the US Department of Labor, and regulates workplace health and safety standards. Due to the toxicity of hydrogen sulfide, and the occupational hazard it poses in certain occupations (such as related to oil and gas extraction and processing, sulfur production, wood pulping, etc), occupational exposure to hydrogen sulfide is restricted.
## Federal OSHA regulations
The federal OSHA standards for workplace exposure to toxic substances can be found tabulated [here](https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9993) and found in the Code of Federal Regulations at 29 CFR 1900.1000 Z.37.2-1966. OSHA standards often include an 8-hour time weighted average (TWA) concentration (e.g. estimated exposure throughout a single workday), a maximum or “ceiling” concentration that should not be exceeded at any point even if its contribution to an 8-hour average would not exceed the 8-hour TWA limit, and occasionally a “peak” concentration that is higher than the ceiling concentration, which cannot be exceeded for fear of injury to life and health.
For hydrogen sulfide, the OSHA enforceable standards do not include an 8-hour TWA limit, but do include a “ceiling” exposure limit of 20 ppm, and a “peak” exposure limit of 50 ppm. The ceiling value can be exceeded once for 10 minutes only if no other measurable exposure occurs during the workday, and that exceedance cannot exceed the peak value.
In addition to these enforceable OSHA standards, the National Institute for Occupational Safety and Health (NIOSH), which is the health research institute that contributes to OSHA’s enforceable standards, recommends a 10-minute ceiling exposure limit of 10 ppm hydrogen sulfide. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends an 8-hour TWA limit of 1 ppm hydrogen sulfide, and a short term exposure limit (STEL; 15 minutes) of 5 ppm hydrogen sulfide. The NIOSH and ACGIH limits are recommendations based on toxicity studies and occupational hazard case studies, but only the OSHA standards are enforceable.
## State occupational exposure regulations
Like environmental regulations, all states must meet the federal occupational safety and health regulations. States may also adopt more robust occupational safety and health standards than the federal minimum, and indeed, 28 states have state plans in addition to meeting federal OSHA requirements. Of the six states for which we’ve gathered hydrogen sulfide regulations information thus far, four of them have adopted the federal OSHA standards, and two have installed additional hydrogen sulfide exposure limits.
Colorado uses the federal OSHA standards for hydrogen sulfide exposure: no 8-hour TWA, 20 ppm ceiling value, and 50 ppm peak value.
Michigan has adopted an 8-hour time weighted average (TWA) exposure maximum and a 15-minute short term exposure limit (STEL) in addition to the federal OSHA ceiling and peak limits. The Michigan 8-hour TWA is 10 ppm, and the 15-minute STEL is 15 ppm.
_Note: It is possible that this is no longer true. In 2012, Governor Rick Snyder ordered that Michigan remove all regulations that were more stringent than federal standards. The Michigan safety and health website is extremely difficult to navigate, and it is unclear whether or not these rules still stand._
Minnesota has adopted an 8-hour time weighted average (TWA) exposure maximum and a 15-minute short term exposure limit (STEL) in addition to the federal OSHA ceiling and peak limits. The Minnesota standards (found [here](http://www.dli.mn.gov/OSHA/PDF/pels.pdf), include the 8-hour TWA of 10 ppm, and the 15-minute STEL of 15 ppm.
Pennsylvania uses the federal OSHA standards for hydrogen sulfide exposure: no 8-hour TWA, 20 ppm ceiling value, and 50 ppm peak value.
Texas uses the federal OSHA standards for hydrogen sulfide exposure: no 8-hour TWA, 20 ppm ceiling value, and 50 ppm peak value.
Wisconsin uses the federal OSHA standards for hydrogen sulfide exposure: no 8-hour TWA, 20 ppm ceiling value, and 50 ppm peak value.
1. Agency for Toxic Substance and Disease Registry. 2016. Hydrogen Sulfide Fact Sheet. https://www.atsdr.cdc.gov/ToxProfiles/tp114-c1-b.pdf (note: it is unclear what original data was used to arrive at the conclusion that H2S usually lasts in environment 1-42 days).
2. Environmental Protection Agency. Risk Management Plan Rule. https://www.epa.gov/rmp. ...