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Hazardous Gases: Hydrogen Sulfide

Table of Contents
Hydrogen sulfide is exceptionally hazardous, due to its high levels of flammability and toxicity. Personnel should be aware of the potential risks.
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What is Hydrogen Sulfide ?

Chemical Compound: H2S

Hydrogen sulfide is a colourless, poisonous gas with a sweet taste. It is often referred to by miners as ‘stinkdamp’ due to its pungent odour, resembling rotten eggs. 

Hydrogen sulfide is naturally generated in situ from reservoir biomass and sulfate-containing minerals through microbial sulfate reduction and thermochemical sulfate reduction. Produced from the decay of organic materials, it is found naturally in many underground mine and construction sites. It is a part of volcanic gases, some mineral waters and unrefined carbonaceous fuels, such as natural gas, crude oil, and coal. Further to this, H2S can occur in the refining process as a by-product of oil and gas production.

Safety Hazards of Hydrogen Sulfide


Hydrogen sulfide is exceptionally hazardous, due to its high levels of flammability and toxicity. Personnel should be aware of the potential risks, hazard assessment, and related actions to ensure their safety.

Exposure to hydrogen sulfide most often occurs during the drilling and production of natural gas, crude oil and petroleum products. Additional contact can occur in refineries, oil and gas wells, battery stations and pipelines as well as the transportation of fluids with dissolved H2S.

Due to its heavy density relative to the typical composition of air, the gas tends to pool and stagnate in wells and poorly ventilated areas. Universal occupational exposure limits are set out to eliminate any risk of adverse health effects.  

Exposure Standard Details

Standard NameHydrogen Sulfide
Cas Number7783-06-4
Time Weighted Average (parts per million)10
Time Weighted Average (mg/m3)14
Short Term Exposure Limit (parts per million)15
Short Term Exposure Limit (mg/m3)21

Prolonged exposure to the gas has significant long-term side effects on our health and in extreme cases, can be fatal. As exposure increases, irritation occurs to the nose, throat, lungs and eyes before disturbing the nervous system; in turn causing headaches, vomiting and dizziness. Extreme exposure levels produce anoxia, the absence of oxygen in arterial blood and tissues, paralysing the respiratory system and ultimately resulting in death.


Hydrogen sulfide is a highly flammable and explosive gas; flames can quickly flashback to the source of a leak. H2S can travel considerable distances, forming explosive mixtures in the air in the range of approximately 4.5 – 45%.

Monitoring H2S Levels

The strong odour of Hydrogen sulfide can be detected by smell concentrations as low as 1ppm; however, as an alert system, this is an extremely unreliable method and should not be used.

Hydrogen sulfide can be measured using a gas detector fitted with electrochemical sensors or by using indicator stain tubes. Electrochemical sensors measure gas levels by measuring currents; the required gas undergoes a chemical reaction, producing a current directly proportional to the concentration of gas present in the atmosphere.

The Aura-FX hydrogen sulfide sensor measures H2S levels; ensuring it remains within a safe range of below 10ppm. The sensor emits an initial warning signal at 5ppm, with an alarm sounding when levels reach 10ppm.

Numerous gases associated with mining, tunnelling and underground construction are generalised into combustible, toxic and asphyxiate types. Because of the hazardous nature of these gases and the unique and restrictive structure of underground environments, these gases must be continuously monitored to mitigate risk.

Check out our other articles on hazardous gases including, carbon dioxide, carbon monoxide, and methane.

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