Hydrogen Sulfide


Hydrogen sulfide is the chemical compound with the formula H2S. It is a colourless, very poisonous, flammable gas or colourless liquid at extremely low temperatures or under very high pressure. Hydrogen sulfide has the characteristic foul odour of rotten eggs at very low concentrations. At concentrations between 30-100 ppm, it has sickening sweet odour and the ability to smell it can begin to dull at 50 ppm and be completely lost [1,2].

Uses [3]

Hydrogen sulfide is used in the manufacture of pulp and paper (digesting agent), in tanneries and in sulfide ores. Most man made hydrogen sulfide is produced as a by-product of industry, rather than for industry.

Sources of Emission & Routes of Exposure

Sources of Emission [3]

  • Industry sources: Potential large emitters of hydrogen sulfide are electric power plants (burning coal or fuel oil containing sulfur), oil and gas extraction operations, oil refineries, pulp and paper mills, sewage treatment plants, large pig farms and other confined animal feeding operations, Portland cement kilns, municipal waste landfills, coke ovens, sulfur products and hydrogen sulfide production, asphalt production and storage and geothermal power plants. Most hydrogen sulfide releases are to the air.
  • Diffuse sources: Other potential emitters of hydrogen sulfide are breweries, fertiliser producers, glue manufacturers, processing of ores (Lead, gold, and copper) and sugar beet and sugar cane processing.
  • Natural sources: Hydrogen sulfide is found in coal pits, volcanic gases, natural gas wells, sulfur springs, and decaying organic matter which contains sulfur.
  • Transport sources: Found in car exhaust.
  • Consumer products: It is not believed that there are any consumer products that contain hydrogen sulfide. Some consumer products may release hydrogen sulfide, such as septic tanks and the burning of coal or oil.

Routes of Exposure [4]

The primary route of exposure to hydrogen sulfide for both workers and the general population is inhalation. The gas is absorbed rapidly by the lungs. Oral and dermal are both minor routes of exposure; these routes only contribute a small amount to the overall body burden.

Health Effects [5]

Hydrogen sulfide is both an irritant and a chemical asphyxiant with effects on both oxygen utilisation and the central nervous system. Its health effects can vary depending on the level and duration of exposure. Repeated exposure can result in health effects occurring at levels that were previously tolerated without any effect. Low concentrations irritate the eyes, nose, throat and respiratory system (e.g., burning/tearing of eyes, cough, shortness of breath). Asthmatics may experience breathing difficulties. The effects can be delayed for several hours, or sometimes several days, when working in low-level concentrations. Repeated or prolonged exposures may cause eye inflammation, headache, fatigue, irritability, insomnia, digestive disturbances and weight loss. Moderate concentrations can cause more severe eye and respiratory irritation (including coughing, difficulty breathing, accumulation of fluid in the lungs), headache, dizziness, nausea, vomiting, staggering and excitability. High concentrations can cause shock, convulsions, inability to breathe, extremely rapid unconsciousness, coma and death. Effects can occur within a few breaths, and possibly a single breath.

Hydrogen sulfide is not known to cause cancer. No human or animal information was located. The International Agency for Research on Cancer (IARC) has not evaluated the carcinogenicity of this chemical.


First Aid Measures [2]

  • Inhalation: H2S is extremely flammable and very toxic. Take proper precautions to ensure your own safety before attempting rescue (e.g. remove any sources of ignition, wear appropriate protective equipment, use the buddy system). Remove source of contamination or move victim to fresh air. If breathing is difficult, trained personnel should administer emergency oxygen. DO NOT allow victim to move about unnecessarily. Symptoms of pulmonary oedema can be delayed up to 48 hours after exposure. If breathing has stopped, trained personnel should begin artificial respiration (AR) or, if the heart has stopped, cardiopulmonary resuscitation (CPR) or automated external defibrillation (AED) immediately. Avoid mouth-to-mouth contact by using mouth guards or shields. Quickly transport victim to an emergency care facility. NOTE: Victims who have been exposed to 500 ppm or higher may pose a threat to responders due to H2S released from their clothing, skin and exhaled air.
  • Skin Contact:
  • GAS: Remove, double bag, seal, label and leave contaminated clothing, shoes and leather goods at the scene for safe disposal. Any skin contact will involve significant inhalation exposure.
  • LIQUEFIED GAS: Quickly remove victim from source of contamination and briefly flush with lukewarm, gently flowing water. DO NOT attempt to rewarm the affected area on site. DO NOT rub area or apply dry heat. Gently remove clothing or jewellery that may restrict circulation. Carefully cut around clothing that sticks to the skin and remove the rest of the garment. Loosely cover the affected area with a sterile dressing. DO NOT allow the victim to drink alcohol or smoke. Quickly transport victim to an emergency care facility. Double bag, seal, label and leave contaminated clothing, shoes and leather goods at the scene for safe disposal.
  • Eye Contact:
  • GAS: If irritation occurs, immediately flush the contaminated eye(s) with lukewarm, gently flowing water for 15-20 minutes, while holding the eyelid(s) open. Immediately obtain medical attention. Any eye contact will also involve significant inhalation exposure.
  • LIQUEFIED GAS: Quickly remove victim from source of contamination. Immediately and briefly flush eye(s) with lukewarm, gently flowing water until the chemical is removed. DO NOT attempt to rewarm. Cover both eyes with a sterile dressing. DO NOT allow victim to drink alcohol or smoke. Quickly transport victim to an emergency care facility.
  • Note to Physicians: Amyl nitrite has been recommended as an antidote to hydrogen sulfide toxicity. However, its use is controversial, as researchers have concluded that it can only be effective within the first few minutes following exposure and may actually slow sulfide removal thereafter. A recent review concludes that nitrite therapy, although not entirely free of controversy, should be considered if the level of medical preparedness and supervision is sufficient to carry out this procedure safely and efficiently.

Storage [5]

Store cylinders in a well-ventilated, secure area, protected from the weather. Cylinders should be stored up-right with valve outlet seals and valve protection caps in place. Storage should be away from heavily travelled areas and emergency exits. There should be no sources of ignition. All electrical equipment should be explosion-proof in the storage areas. Storage areas must meet National Electrical Codes for Class 1 hazardous areas. Flammable storage areas should be separated from oxygen and other oxidisers by a minimum distance of 20 ft. or by a barrier of non-combustible material at least 5 ft. high, having a fire resistance rating of at least 1/2 hour. Post “No Smoking or Open Flames” signs in the storage and use areas. Do not allow storage temperature to exceed 125 °F (52 °C). Full and empty cylinders should be segregated. Use a first-in, first-out inventory system to prevent full containers from being stored for long periods of time. Consideration should be taken to install leak detection and alarm equipment for storage areas.

Exposure Control & Personal Protection [5]

  • Engineering Controls

  • Ventilation: Hydrogen Sulfide detectors should be installed in or near areas where the chemical is being used or stored. If appropriate, install automatic monitoring equipment to detect the level of oxygen and the presence of potentially explosive air-gas mixtures. Because of the high hazard associated with H2S, stringent control measures such as a gas cabinet enclosure or isolation may be necessary. Provide natural or explosion-proof ventilation adequate to ensure it does not reach exposure limits. Local exhaust ventilation is preferred, because it prevents gas dispersion into the work place by eliminating it at its source.

  • Respiratory Protection: Maintain exposure levels of H2S below recommended exposure level. Use supplied air respiratory protection if levels exceed exposure limits or during emergency response to a release of this product. If respiratory protection is required, follow the requirements of the Federal OSHA Respiratory Protection Standard (29 CFR 1910.134), or equivalent State standards. NIOSH respiratory protection recommendations for hydrogen sulfide are: Up to 100 ppm – Powered airpurifying respirator, gas mask with canister, SAR or full-facepiece SCBA.
  • Eye Protection: Safety glasses. Additionally, face-shields should be worn if there is a potential for contact with liquid H2S. Eye wash stations/safety showers should be near areas where the chemical is used or stored.
  • Skin Protection: Work gloves are recommended when handling cylinders of H2S. Use thermally insulated gloves when working with containers of Liquid H2S. Wear chemically-resistant gloves when using this gas. Butyl rubber, chlorinated polyethylene, neoprene nitrile, and polyvinyl rubber are recommended. Use fire-resistant gloves and clothing in emergency situations. Use double gloves for spill response.
  • Other protective Clothing: Use body protection appropriate for task. Static-resistant clothing is recommended. Safety shoes are recommended when handling cylinders. Transfer of large quantities under pressure may require use of fire retardant and/or chemically impervious clothing


United States [7]

OSHA: The Occupational Safety & Health Administration has set the following permissible exposure limits (PEL) for hydrogen sulfide:

  • General Industry: 29 CFR 1910.1000 Z-2 Table — Exposures shall not exceed 20 ppm (ceiling) with the following exception: if no other measurable exposure occurs during the 8-hour work shift, exposures may exceed 20 ppm, but not more than 50 ppm (peak), for a single time period up to 10 minutes.
  • Construction Industry: 29 CFR 1926.55 Appendix A — 10 ppm, 15 mg/m3 TWA
  • Maritime: 29 CFR 1915.1000 Table Z-Shipyards — 10 ppm, 15 mg/m3 TWA

ACGIH: The American Conference of Governmental Industrial Hygienists has established the following Threshold Limit Value (TLV) for hydrogen sulfide: 1 ppm, 14 mg/m3 TWA; 15 ppm, 21 mg/m3 STEL

NIOSH: The National Institute for Occupational Safety and Health has set the following Recommended Exposure Limits (REL) for hydrogen sulfide: 10 ppm, 15 mg/m3 Ceiling (10 Minutes)

NIOSH has set a concentration of 100 ppm as IDLH (immediately dangerous to life and health).

Australia [3]

Safe Work Australia: For hydrogen sulfide, it is allowable for workers to be exposed to concentrations of 10 parts per million, averaged over an eight hour workshift, with the exposure not exceeding 15 parts per million.

Australian Drinking Water Quality Guidelines (NHMRC and ARMCANZ, 1996): Aesthetic: Maximum of 0.05 mg/L (i.e. 0.00005 g/L).

United Kingdom [8]

Hydrogen sulfide has a WEL of 5 ppm 8-hour TWA based on data indicating a shift towards anaerobic respiration at exposures to 10 ppm.