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Hydrogen Sulfide H2S Gas Detection & Gas Detectors

Sierra Monitor has several different Hydrogen Sulfide gas detectors dependent upon the application.

Hydrogen Sulfide (H2S) is a colorless, very poisonous, potentially flammable gas with the characteristic foul odor of rotten eggs perceptible at very low concentrations. It often results from bacterial breakdown of organic matter in the absence of oxygen such as in sewers.

Typical applications where dangerous levels of Hydrogen Sulfide (H2S) might occur and benefit from a Hydrogen Sulfide gas detector are:

    • Crude petroleum production
    • Petroleum refineries
    • Coke ovens
    • Paper Mills
    • Tanneries

Hydrogen Sulfide is considered a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous system is the most affected. It forms a complex bond with iron in the mitochondrial cytochrome enzymes, thus preventing cellular respiration.

Exposure Limits (Source: OSHA)

Following are Hydrogen Sulfide exposure limits that industries should be aware of when researching Hydrogen Sulfide gas detectors and gas detection systems.

Agency Exposure Limits
OSHA PEL (General Industry) 20 ppm (ceiling)
OSHA PEL (Construction Industry) 10 ppm TWA
OSHA PEL (Maritime) 10 ppm TWA
ACGIH TLV 10 ppm TWA, 15 ppm STEL
NIOSH REL 10 ppm Ceiling (10 minutes)
NIOSH IDLH 100 ppm


  • TWA = Time Weighted Average exposure concentration for a normal 8-hour workday and 40-hour workweek
  • STEL = Short Term Exposure Limit (Usually a 15-minute time-weighted average exposure that should not be exceeded at any time during a workday
  • NIOSH (National Institute for Occupational Safety and Health)
    • REL = Recommended Exposure Limit
    • IDLH = Immediately Dangerous to Life or Health Concentration
  • OSHA (Occupational Safety and Health Administration)
    • PEL = Permissible Exposure Limit
  • ACGIH (American Conference of Government Industrial Hygienists)
    • TLV = Threshold Limit Value

Hydrogen Sulfide (H2S) Properties

  • Toxic & Hazardous Properties

    Hydrogen sulfide is extremely toxic, comparable to hydrogen cyanide and carbon monoxide. It is a “broad-spectrum poison,” i.e. one capable of poisoning several different bodily systems; the nervous system is the most affected. H2S forms a complex bond with iron in the body’s mitochondrial cytochrome enzymes, and therefore prevents cellular respiration.

    Hydrogen sulfide does occur naturally in the human body. Enzymes in the body are capable of detoxifying it into a harmless sulfate via oxidation. Because of this, low levels of H2S can be tolerated indefinitely. However, at concentrations of around 300 to 350 parts per million (ppm), the oxidative enzymes are overwhelmed.

    Exposure to lower concentrations of hydrogen sulfide can cause eye irritation, cough, sore throat, shortness of breath, nausea, and pulmonary edema (fluid in the lungs). These effects are most likely caused by the caustic sodium sulfide created when H2S combines with alkalis in the body’s moist surface tissues. Prolonged low level exposure to hydrogen sulfide can lead to fatigue, headaches, irritability, dizziness, loss of appetite, and impaired memory.

    Exposure to higher levels of H2S causes far more severe symptoms, which worsen with increased concentration. At 530 ppm and up, hydrogen sulfide causes strong stimulation of the central nervous system and rapid breathing, often leading to loss of breathing. 800 pm is lethal for 50% of humans after just five minutes of exposure. At 1000 ppm, immediate collapse and loss of breathing can occur after inhalation of a single breath. Respiratory paralysis is generally immediate, but it may be delayed up to 72 hours.

    In addition to its high toxicity, hydrogen sulfide is flammable and corrosive. A mixture of H2S and air is highly explosive; hydrogen sulfide mixed with pure oxygen will burn with a hot, blue flame, producing sulfur dioxide (SO2) and water. As it is heavier than air, H2S often accumulates at the bottom of poorly-ventilated spaces.  For this reason, a hydrogen sulfide detector or hydrogen sulfide sensor is of the utmost importance in facilities that produce and/or use hydrogen sulfide.

    H2S is soluble in water; the two combined will create a weak acid called sulfhydric acid or hydrosulfuric acid. Gaseous hydrogen sulfide, when put in contact with concentrated nitric acid, will explode.

    A high level of hydrogen sulfide in the Earth’s atmosphere is thought to have caused the Permian-Triassic extinction event approximately 252 million years ago, killing 96% of the planet’s marine species and 70% of its terrestrial vertebrae.

    Environments Where H2S Exposure May Occur

    In addition to sewers and swamps, hydrogen sulfide often occurs naturally in volcanic gases, natural gas, various biogases, and some well waters. Volcanoes emit H2S produced via the hydrolysis of sulfide minerals. Natural gas can sometimes be as much as 90% hydrogen sulfide (natural gas with high H2S content is known as “sour gas”). Sulfate-reducing bacteria can create H2S in well water.

    Apart from its natural occurrences, hydrogen sulfide can also be created, either intentionally or as a byproduct, in a number of industrial processes. Hydrogen sulfide is also commonly produced for scientific purposes.

    Petroleum production and refinement are by far the largest industrial producers of H2S. As a result of the hydrodesulfurization process, sulfur is extracted from petroleum by the action of hydrogen. Hydrodesulfurization catalysts are commonly activated using hydrogen sulfide. Metallic catalysts used in other refinery processes are also frequently modified using H2S.


    The most common method for intentionally producing hydrogen sulfide is via its separation from sour gas. H2S-rich natural gas is pumped through a container hydrated with iron (III) oxide, which combines with hydrogen sulfide. Throughout the extraction phase, this system is completely passive. Alternatively, natural gas containing H2S can be streamed through an impregnated activated carbon filter; this method can also be used to extract hydrogen sulfide from biogases.

    H2S can also be produced by reacting hydrogen gas or hydrocarbons with elemental sulfur at temperatures of 450°F or more. Standard lab preparation of H2S involves reacting ferrous sulfide with a strong acid in a Kipp generator; reacting aluminum sulfide with water produces the same results.

    Hydrogen sulfide is a byproduct of many chemical reactions—caution should be exercised anywhere production has the potential to occur. H2S can be created by almost any process in which elemental sulfur comes into contact with organic materials, especially high temperature processes.

    Uses of Hydrogen Sulfide

    Hydrogen sulfide has a range of uses in scientific, industrial, metallurgical, and other applications.

    It can be used to produce organosulfur compounds such as methanethiol, ethanethiol, and thioglycolic acid. Organosulfur compounds can be used in everything from medicines to chemical warfare.

    H2S can be combined with alkali metal bases to create alkali hydrosulfides, such as sodium sulfide. Among other uses, alkali hydrosulfides are used in the depilation of animal hides in tanneries and as part of the Kraft process for the delignification of wood pulp in paper milling.

    Though it has largely been replaced by thioacetamide for this process, hydrogen sulfide can be used in analytic chemistry for the qualitative inorganic analysis of metal ions. Upon exposure to H2S, heavy metal and nonmetal ions can be precipitated from solutions and selectively redissolved.

    To purify metal ores via flotation, mineral powders can be treated with hydrogen sulfide to enhance separation. Some metal parts can be passivated using H2S. Using the Girdler Sulfide process, hydrogen sulfide can also be used to separate heavy water (deuterium oxide) from normal water.