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The Hazards of Hydrogen Sulfide

The Hazards of Hydrogen Sulfide

What is Hydrogen Sulfide?

Hydrogen sulfide (H₂S), a chemical compound, is a colorless gas that has an overpowering odor likened to rotten eggs. Hydrogen sulfide is naturally produced when organic materials undergo a microbial breakdown and oxygen is absent. Hydrogen sulfide is heavier than air and therefore found in low lying areas. H₂S is poisonous and considered highly toxic to human health. This is because H₂S akin to carbon monoxide (CO) prevents cellular respiration. Hydrogen sulfide is also flammable, highly reactive, and is a corrosive agent.

hydrogen sulfide dangersWhere is Hydrogen Sulfide Found?

As a naturally produced gas from decaying organic matter, hydrogen sulfide can be released from garbage landfills, sewage sludge, swamps, liquid manure, hot sulfur springs, well water, and oil and gas wells. H₂S also can be found in natural and volcanic gases. Hydrogen sulfide is commonly used and produced by several industries including oil and gas, mining, pulp and paper processing, and rayon manufacturing. Processes such as petrochemical refining, oil and gas drilling, wastewater treatment, sewerage operations, and hot asphalt paving can release hydrogen sulfide as a by-product. Hence, hydrogen sulfide may be found in underground tanks, sewers, manure storage tanks, manure pits, tunnels, wells, and confined spaces; around refining operations and livestock; and while processing pulp, paper, and textiles.

When Does Hydrogen Sulfide Gas Become Dangerous to Human Health?

Hydrogen sulfide is present in the atmosphere at low levels, it is also released as exhaust from cars. Such low levels of exposure to H2S is considered a part of our daily lives. However, care must be taken when exposure occurs in occupational settings. This is because the length of exposure, the quantity of H₂S gas exposed to, the route of exposure, and an individual’s preexisting medical conditions together with age, dietary habits, and other personal factors can impact the toxicity of exposure to hydrogen sulfide. As a result, both OSHA and NIOSH provide guidance to protect workers from H₂S exposure in occupational settings. Hydrogen sulfide exposure at or above 100 ppm (parts per million) is considered immediately dangerous to life and health (IDLH) as stated by NIOSH, while OSHA provides worker exposure limits using an enforceable permissible exposure limit (PEL) level for different industries and timeframes.

The table below gives guidance on worker exposure limits.

Worker Exposure Limits

NIOSH REL (10-min. ceiling): 10 ppm
General Industry Ceiling Limit: 20 ppm
General Industry Peak Limit: 50 ppm (up to 10 minutes if no other exposure during shift)
Construction 8-hour Limit: 10 ppm
Shipyard 8-hour limit: 10 ppm
NIOSH IDLH: 100 ppm
  • IDLH: immediately dangerous to life and health (the level that interferes with the ability to escape) (NIOSH)
  • PEL: permissible exposure limit (enforceable) (OSHA)
  • ppm: parts per million
  • REL: recommended exposure limit (NIOSH)

Table Source: OSHA. (n.d.). Hydrogen Sulfide – Hazards. Website https://www.osha.gov/SLTC/hydrogensulfide/hazards.html

What are the Routes of Hydrogen Sulfide Exposure?

There are several main routes of worker exposure to hydrogen sulfide.

Breathing (Inhalation)

The most likely and common route of exposure to H₂S is breathing in the gas. Workers in occupations where hydrogen sulfide is produced as a by-product and working in windless or low-lying areas, in hot weather conditions, in confined spaces, or close to swamps are more likely to be exposed to higher doses of H₂S in the atmosphere. Inhalation of the H₂S gas can also occur due to accidental releases. While people can smell the rotten egg odor of H₂S, continuous low-level exposure or sudden high concentrations of hydrogen sulfide results in the loss of the ability to smell the H₂S gas, known as olfactory fatigue. Therefore, using smell to detect H₂S in the air is not a reliable method.

Touching (Absorption through the Skin or Eye)

Touching is another method of exposure to hydrogen sulfide. Workers would be exposed if they touch other materials that contain H₂S or have direct contact with liquid hydrogen sulfide. Workers exposed to H₂S even in low concentrations may absorb the gas through the eyes.

Drinking (Ingestion)

As water can be contaminated with H₂S, any worker working in an industry where hydrogen sulfide is produced or used has a possibility of being exposed through this route.

What are the Symptoms and Health Hazards Associated with Hydrogen Sulfide Exposure?

Employees who may be exposed to hydrogen sulfide must be aware that hydrogen sulfide has an adverse impact on the human respiratory system, central nervous system, cardiovascular system, renal system, and the skin and eyes. The below symptoms and health hazards associated with H₂S exposure impact the above mentioned human biological systems. The severity of the symptoms and the associated health problems are dependent on the length and dose of exposure among other factors. Hence, undergoing regular medical checkups is advised if working in occupations with exposure to hydrogen sulfide.

1.  Skin irritation 8.  Chronic cough 15.  Irritability
2.  Eye irritation 9.  Fluid in the lungs 16.  Headache
3.  Throat irritation 10.  Low blood pressure 17.  Loss of appetite
4.  Shortness of breath 11. Weight loss 18. Memory problems
5.  Eye-membrane inflammation 12. Nausea 19. Loss of consciousness leading to falls and other injuries
6.  Dermatitis 13.   Tiredness
7.  Frostbite 14.  Dizziness

The Hazards of Hydrogen SulfideWhat can Employers do to Safeguard Worker Safety and Health?

Following OSHA and NIOSH recommendations will enable employers to safeguard workers exposed to hydrogen sulfide. Employers must employ the Hierarchy of Controls to safeguard workers’ health and apply relevant engineering controls, administrative controls, and work practice controls within the workplace. Furthermore, as required, workers must be provided with personal protective equipment (PPE) such as a full facepiece pressure-demand self-contained breathing apparatus (SCBA) and personal H₂S detectors. Regularly undertaking air monitoring in areas with possible exposure to hydrogen sulfide and installing hydrogen sulfide detectors in case of a gas leak are good practices to implement at the worksite. In addition, employers must ensure that employees exposed to or with the possibility of exposure to hydrogen sulfide be given adequate training and knowledge to:

  • Understand the characteristics of hydrogen sulfide;
  • Identify sources which produce and release the H₂S gas;
  • Explain the safety and health hazards of H₂S exposure;
  • Distinguish the different occupational exposure limits of H₂S given by various organizations;
  • Understand the symptoms of H₂S exposure;
  • Understand the need for medical surveillance when working in occupations with the possibility of H₂S exposure;
  • Understand the Hierarchy of Controls and how it is applicable; and
  • Enact first-aid procedures when exposed to hydrogen sulfide.

Employers can provide this training using a combination of online and classroom training as well as on-site and on-the-job training.

HAZWOPER-OSHA provides a comprehensive online training course for Hydrogen Sulfide Awareness. Employees working in occupations and industries with possible exposure to H₂S can enroll for the Hydrogen Sulfide Awareness online training today!




Delaware Health and Social Services – Division of Public Health. (2013, September, Revised). Frequently Asked Questions: Hydrogen Sulfide [PDF]. Website. https://dhss.delaware.gov/dhss/dph/files/hydsulffaq.pdf

OSHA. (2005, October). OSHA Fact Sheet – Hydrogen Sulfide (H2S) [PDF]. Website. https://www.osha.gov/sites/default/files/publications/hydrogen_sulfide_fact.pdf

OSHA. (n.d.). Hydrogen Sulfide – Hazards. Website https://www.osha.gov/hydrogen-sulfide/hazards

OSHA. (n.d.). Hydrogen Sulfide – Overview. Website. https://www.osha.gov/hydrogen-sulfide




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