What Is H2S

What is H2S? H2S, also known as Hydrogen sulfide, is a colorless gas with a distinct “rotten egg” odor at low concentrations. It is exceedingly flammable and poisonous. In the United States, hydrogen sulfide is one of the most common causes of workplace gas inhalation mortality. Sewer gas, smelly damp, swamp gas, and manure gas are frequent names for H2S gas.

What Is H2S

What Is H2S

Hydrogen sulfide emits a pungent “rotten egg” odor in low quantities. It is exceedingly flammable and poisonous.

Hydrogen sulfide is utilized or generated in various industries, including those listed below:

Hydrogen sulfide is found in sewers, waste pits, well water, oil and gas wells, and volcanoes.

Hydrogen sulfide can concentrate in low-lying and enclosed places, such as manholes, sewers, and underground telephone vaults since it is heavier than air. Because of its presence, working in confined places can be quite risky.

The health effects of hydrogen sulfide are dependent on how much and how long worker breaths it. Even at modest quantities, however, significant impacts are observed.

The effects can be moderate, such as headaches or eye irritation, or severe, such as unconsciousness and death.

This article explains how hydrogen sulfide can impact your health, where you can find it, and how to avoid dangerous exposures.

Health Risks

The health impacts of hydrogen sulfide gas are numerous. Workers are mostly exposed to hydrogen sulfide by inhalation.

The consequences are determined by how much hydrogen sulfide you breathe and how long you breathe it. Exposure to extremely high concentrations can result in death in a matter of minutes.

The following are examples of short-term (also known as acute) symptoms and effects:

Concentration(ppm) Symptoms/Effects
0.00011-0.00033 Background concentrations that are typical
0.01-1.5 The threshold for odor (when rotten egg smell is first noticeable to some). At 3-5 ppm, the odor gets more irritating. The odor is regarded as pleasant or sickeningly sweet when it exceeds 30 ppm.
2-5 Long-term exposure can result in nausea, tearing of the eyes, headaches, and insomnia. Some asthma sufferers experience airway issues (bronchial constriction).
20 Fatigue, loss of appetite, headaches, irritability, impaired memory, and dizziness are all possible symptoms.
50-100 After 1 hour, mild conjunctivitis (“gas eye”) and respiratory tract discomfort develop. It is possible that it will disturb your stomach and make you lose your appetite.
100 After 2-15 minutes, you may experience coughing, eye irritation, and a loss of scent (olfactory fatigue). After 15-30 minutes, you may have altered breathing and tiredness. After 1 hour, there was throat irritation. Over the course of several hours, the severity of the symptoms gradually increases. After 48 hours, death may ensue.
100-150 a loss of odor (olfactory fatigue or paralysis).
200-300 After 1 hour, there was noticeable conjunctivitis and respiratory tract discomfort. Prolonged exposure can cause pulmonary edema.
500-700 Staggering, with a 5-minute collapse. In 30 minutes, serious eye damage has occurred. After 30-60 minutes, death occurs.
700-1000 Within 1 to 2 breaths, fast unconsciousness, “knockdown” or abrupt collapse, breathing stops, and death occurs within minutes.
1000-2000 Death is almost instantaneous

What about the long-term health consequences? After waking up, some people who inhaled high enough levels of hydrogen sulfide to fall unconscious still experience headaches and poor attention span, memory, and motor function.

At exposures over permissible exposure limits, problems with the cardiovascular system have also been recorded. Asthmatics may be more susceptible to hydrogen sulfide exposure. Individuals may have trouble breathing at lower levels than persons who do not have asthma.

Hydrogen Sulfide Safety Hazards

Hydrogen sulfide is an extremely flammable, explosive gas that can result in life-threatening situations if not handled properly. Furthermore, when hydrogen sulfide gas is burned, it produces other harmful vapors and gases, including sulfur dioxide.

Liquid hydrogen sulfide can induce “blue skin” or frostbite in addition to exposure to hydrogen sulfide in the air. If clothing becomes wet, keep it away from ignition sources, remove it, and place it in a secure place to dry.

The knockdown effect (rapid unconsciousness) frequently leads to falls that badly damage the worker.

More information about hydrogen sulfide’s safety and health consequences can be found in the following resources:

  • Fact Sheet from OSHA (October 2005). Provides a quick reference guide to industrial sources, symptoms and health impacts of hydrogen sulfide exposure, and OSHA requirements for worker protection.

  • OSHA QuickCardTM is an acronym for Occupational Safety and Health Administration. Provides important hydrogen sulfide safety measures.

  • Hydrogen Sulfide is a gas made up of hydrogen and sulfur. Workplace Safety and Health is covered by the National Institute for Occupational Safety and Health (NIOSH). This page contains a list of NIOSH and related hydrogen sulfide resources.

  • A Pocket Guide from the National Institute of Occupational Safety and Health. Publication No. 2005-149 of the National Institute for Occupational Safety and Health (NIOSH). Physical descriptions, exposure limits, measuring methods, personal protection and sanitation, first aid, respirator recommendations, exposure pathways, symptoms, target organs, and other hydrogen sulfide information.

  • The National Institute for Occupational Safety and Health (NIOSH) is a federal agency that promotes workplace safety and health (Revised August 16, 1996). Explains how NIOSH concluded that hydrogen sulfide is Immediately Dangerous to Life and Health (IDLH).

  • The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal agency that regulates toxic substances and diseases (July 2006). Answers the most common inquiries about hydrogen sulfide’s health effects.

  • The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal agency that regulates toxic substances and diseases (July 2006). More scientific details on hydrogen sulfide, including health impacts, physical and chemical properties, human exposure potential, and analytical procedures.

  • The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal agency that regulates toxic substances and diseases (April 2006). Provides general information about hydrogen sulfide, its health implications, and medical therapies for hydrogen sulfide poisoning.

What Is H2S

Workplaces with Hydrogen Sulfide

Hydrogen sulfide is formed spontaneously when organic stuff decomposes. Sewage sludge, liquid manure, sulfur hot springs, and natural gas can all emit it.

It is also used or produced as a by-product in a variety of industrial operations, including:

Many people are in danger of hydrogen sulfide poisoning, especially those who work in tight places. As an example:

  • Sanitation personnel may be exposed when cleaning or servicing city sewers and septic tanks.

  • Farmworkers may be exposed when cleaning sewage holding tanks or working in sewage pits.

  • Workers in the oil and natural gas drilling and refining industries may be exposed to hydrogen sulfide, which is a by-product of the desulfurization process of these fuels and may be present in oil and gas deposits.

Working in the following places and conditions, in general, increases a worker’s risk of hydrogen sulfide overexposure:

  • Hydrogen sulfide can start building up to dangerous amounts in confined places (pits, manholes, tunnels, and wells).

  • Windless or low-lying locations enhance the chance of hydrogen sulfide pockets forming.

  • Bacteria convert organic materials to generate hydrogen sulfide in marshy settings.

  • The decomposition of manure and other organic materials is accelerated by hot weather, increasing the hydrogen sulfide evaporation rate.

Controlling and Evaluating Exposure

To protect workers from dangerous hydrogen sulfide exposures, implement the following measures:

  • Determine whether H2S gas is present and at what levels by evaluating the exposure.

  • When possible, eliminate the cause of hydrogen sulfide.

  • Control exposures if the cause cannot be eliminated:

    • The next effective line of defense is to use engineering controls.

    • To decrease exposures to safe levels, develop administrative controls and safe work practices.

  • If engineering measures and work practices alone are not enough to limit hydrogen sulfide to acceptable levels, use personal protective equipment.

Assess The Level Of Exposure

Evaluating exposure are as follows:

  • Determine which processes may release or produce hydrogen sulfide. This includes locating known hydrogen sulfide sources and assessing potential fire and burst dangers. To identify and control dangers, use a process or job hazard analysis.

  • Hydrogen sulfide should be tested (monitored) in the air. This should be done by a professional. Use the proper test equipment, such as a hydrogen sulfide gas electronic meter.

  • Perform air monitoring before and at regular intervals during any job activity to expose you to hydrogen sulfide. Air monitoring must be carried out under OSHA regulations when operating in confined places. Monitors like detector tubes, direct reading gas monitors, alarm only gas monitors, and ■■■■-up meters may be used to test allowed space atmospheres.

  • Atmospheric Testing in Confined Spaces Procedures Fact Sheet from OSHA. The need to assess the hazards of a restricted place and ensure that suitable conditions for entry exist is discussed.

General information on atmospheric testing methods:

  • The Occupational Chemical Database is maintained by the Occupational Safety and Health Administration (OSHA). OSHA’s one-stop-shop for information on occupational chemicals. It assembles data from a variety of government agencies and organizations. Chemical identification and physical attributes, exposure limits, sampling information, and supplementary resources are all available on the pages.

  • Hydrogen Sulfide is a gas made up of hydrogen and sulfur. Sampling and Analytical Method 1008 of the Occupational Safety and Health Administration. The collection of airborne hydrogen sulfide utilizing a personal sampling pump and specifically manufactured hydrogen sulfide samplers with silver nitrate coated silica gel is described.

  • Method 6013 of the National Institute of Occupational Safety and Health. Ion chromatography is used to evaluate air samples taken with a glass tube and personal sampling pump.


DO NOT rely on your ability to smell to detect hydrogen sulfide’s presence or notify you if dangerous levels are present.

At low concentrations in the air, hydrogen sulfide emits a “rotten egg” odor. However, after a period, even though the gas is still present, you lose your capacity to smell it (olfactory fatigue).

This loss of smell can occur quickly and at high doses. The sense of smell for the gas may be completely lost (olfactory paralysis).

What Is H2S

Limit Your Exposures

To lower hydrogen sulfide levels, use exhaust and ventilation systems. Check to see if the system is:

  • Non-sparking

  • Grounded

  • Corrosion-resistant

  • Other exhaust systems are not connected to this system.

  • Blast proof

As hydrogen sulfide is combustible and can damage things if not adequately protected, these precautions are necessary. When operating in confined places, ventilation should be maintained at all times and carried out under OSHA regulations.

Workers Should Be Trained And Educated On Hazards And Controls

The following are examples of possible training topics:

  • Hydrogen sulfide: properties, sources, and health risks.

  • Hydrogen sulfide poisoning symptoms.

  • Methods for detecting hydrogen sulfide and the exposure limits that apply.

  • Practices and procedures in the workplace to prevent hydrogen sulfide exposure.

  • Emergency planning, safety equipment placements, rescue tactics, and first-aid.

  • Procedures for working in confined spaces.

Rescue Techniques

Establish suitable rescue techniques to safely save someone who has been exposed to hydrogen sulfide. Before entering regions with high amounts of hydrogen sulfide, first responders must be adequately educated and protected.

The following should be included in the rescuer’s protection:

  • Self-contained positive-pressure breathing device (SCBA).

  • A safety line that allows for a quick evacuation if situations deteriorate.

Use Respiratory And Other PPE To Protect Yourself

To protect yourself read the following:

  • Employers are required to provide breathing protection and other personal protective equipment (PPE), such as protective eyewear and possibly fire-resistant clothing if engineering and administrative procedures do not successfully reduce hydrogen sulfide to below OSHA’s permitted exposure threshold.

  • Before starting any job activity, employers must conduct a PPE hazard assessment and equipment selection process under OSHA standards. At the very least, respiratory protection should include:

    • Use an air-purifying respirator with hydrogen sulfide-specific canisters/cartridges for exposures below 100 ppm. Eye protection will be provided with a full-face respirator.

    • Use a full-face pressure-demand self-contained breathing equipment (SCBA) with a minimum service life of thirty minutes for exposures at or above 100 ppm or a combination full-face pressure-demand supplied-air respirator with an auxiliary self-contained air supply for exposures at or above 100 ppm. Exposures of 100 ppm or above are regarded as instantly hazardous to one’s life and health (IDLH).

  • Employers must establish a respiratory protection program that meets the standards of OSHA’s Respiratory Protection standard whenever respirators are employed (29 CFR 1910.134). Proper respirator selection, fit testing, medical examinations, and training must all be part of this approach.


Hydrogen sulfide (H2S) is a hydrogen-sulfur gas. Before accessing areas with high levels of H2S, first responders must be fully informed and protected. Employers must offer respirators and other personal protective equipment (PPE).

Frequently Asked Questions (FAQs)

Many people have questions regarding “What is H2S,” and a few of them are answered below:

1. What does H2S mean?

Hydrogen sulfide is a transparent, combustible, exceedingly dangerous gas that smells like rotten eggs. Sewer gas, smelly damp, swamp gas, and manure gas are all frequent names for the gas.

2. What is the purpose of H2S?

Hydrogen sulfide is a by-product of various industrial operations, including oil refining, mining, tanning, wood pulp processing, food processing, handmade papermaking, and rayon manufacturing.

3. Why is H2S so lethal?

Since H2S is heavier than air, it may settle in low areas. This can result in danger when accessing regions where the gas is present. H2S is a very flammable and explosive gas. When H2S burns, it produces hydrogen sulfide, another poisonous, pungent-smelling, irritating gas.

4. Is H2S toxic to humans?

Hydrogen sulfide irritates the eyes, nose, and throat at low concentrations. Moderate amounts can result in headaches, dizziness, nausea, vomiting, coughing, and difficulty breathing. Higher concentrations can result in shock, convulsions, coma, and death.

5. Is hydrogen a gas?

H2, with an atomic mass of 1.00794, is an elementary gas. This diatomic molecule is the universe’s lightest and most abundant element. Additionally, it is colorless, odorless, and extremely combustible. Hydrogen; The most prevalent element in the universe is hydrogen, abbreviated as H2.

6. What is ppm H2S?

H2S (Hydrogen Sulfide) is an extremely hazardous gas that can kill or gravely damage humans, even at low quantities such as ten parts per million (ppm).

7. Is H2S a flammable gas?

Hydrogen sulfide is an extremely flammable, explosive gas that, if not handled appropriately, can result in potentially fatal scenarios. Furthermore, as hydrogen sulfide gas burns, it emits other harmful vapors and gasses, such as sulfur dioxide.

8. What effect does H2S have on the lungs?

After exposure to high quantities, either immediate or prolonged pulmonary edema ensues. After one or more breaths, high-level breathing results in loss of consciousness and mortality within a few more breaths. Reduced concentrations may cause eye irritation, hoarseness and coughing, difficulty breathing, and pulmonary fluid accumulation.

9. What kind of bond does H2S form?

Hydrogen sulfide is a covalent molecule of two hydrogen atoms bonded to a sulfur atom in the center.

10. What shape does H2S take?

Hydrogen sulfide has a bent molecular structure. Sulfur is linked to two hydrogens in the center.

11. How can I keep track of my H2S?

Hydrogen sulfide should be tested (monitored) in the air. A qualified individual must perform this. Utilize the appropriate testing equipment, such as an electronic meter capable of detecting hydrogen sulfide. Conduct air monitoring before and at regular intervals throughout any job activity resulting in hydrogen sulfide exposure.

12. What is the H2S action level?


The legally permitted exposure limit (PEL) for airborne contaminants is 20 parts per million (ppm), which must not be exceeded at any time, and 50 parts per million (ppm) as a maximum peak concentration that must not be exceeded during any 10-minute working time.


NIOSH recommends that the estimated airborne exposure limit (REL) not exceed ten parts per million (ppm) during any 10-minute work time.

13. Is hydrogen sulfide explosive when combined with air?

Between the upper explosive limit of 46 percent, where the air is too rich to burn, and the lower explosive limit of 4.3 percent, where the air is too thin to burn, hydrogen sulfide is explosive. When combined with air, however, the mixture can be explosive if a source of ignition is present.

14. When is it possible to smell H2S?

Hydrogen sulfide has a low odor threshold. Its stench can be noticed at concentrations as low as 1 part per million. The minimum detectable odor is claimed to be 0.13 parts per million. The rotten egg stench is detectable at up to 30 parts per million concentrations. It has a sweet odor at concentrations of 30 to 100 parts per million.

15. Is H2S carcinogenic?

Is hydrogen sulfide likely to cause cancer? Hydrogen sulfide has not been demonstrated to cause cancer in humans. Its potential in animals has not been properly investigated.


Hydrogen sulfide is a highly combustible, explosive gas that can result in life-threatening situations if not handled properly. Reduced concentrations may irritate the eyes, produce hoarseness, and cause coughing. NIOSH advises that the estimated airborne exposure limit (REL) for any 10-minute work period not exceed ten parts per million.

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