What is Hydrogen Sulfide and Why is it a Lethal Hazard?

Posted on 7/1/2019 by Joel Gregier, CDGP

Depending on the industry you work in (for instance gas and oil), you may need to be cautious of a dangerous gas: hydrogen sulfide.  To protect yourself and co-workers from this gas, you must know the warning signs of exposure and the hazards posed by H2S in the workplace. 

What is Hydrogen Sulfide (H2S)?

Hydrogen sulfide, or H2S, is a colorless, flammable gas that is toxic at extremely low concentrations.  The gas molecule consists of two hydrogen atoms and a single sulfur atom (see image above).

Hydrogen sulfide is heavier than air, and often accumulates in low-lying or enclosed areas, such as gas venting or mud systems, cellars, pits, or tanks, creating areas with very high and very dangerous concentrations of the gas.

H2S smells like rotten eggs at low concentrations and causes those exposed to it to quickly lose their sense of smell, making it very dangerous since workers may not even know it is present.  Exposure to low concentrations of this gas can cause extreme discomfort, such as eye and throat irritation, while higher concentrations can result in respiratory paralysis and death.

Learn more about the hazards of H2S with the Hydrogen Sulfide Safety Online Course, now available at for $29. 

Sources of Hydrogen Sulfide

Hydrogen sulfide forms as a result of microbes breaking down organic material in areas with little or no oxygen. This gas can often be found in natural sources where elemental sulfur comes into contact with organic materials.  For instance, it can be found in volcanic gases, natural gas, and some well water and hot springs.
H2S can also be found around many industrial sources. 

Like hydrogen sulfide, oil and gas are also created by the breakdown of organic materials, and as such, the two are often found together.  As a result, hydrogen sulfide can be present at sites during extraction of natural resources. The refinement of petroleum can also produce hydrogen sulfide when hydrogen is used to remove sulfur from petroleum.

Coke ovens, paper mills that use the sulfate method, and tanneries are also areas where hydrogen sulfide is created.

The most common industries for H2S include gas, oil chemical, geothermal energy, and viscose rayon.  The workplaces that may also have concentrations of this gas can include, but are not limited to, sewer systems, tanneries, mining, smelting, drilling, animal waste disposal, and fishing boats.

Real World Incidents of Hydrogen Sulfide

There have been several incidents involving hydrogen sulfide in the past, many which are not discussed in this article.  However, one of the biggest incidents occurred in Denver City, TX on February 2, 1975.

In this oil-field related accident, a very small leak of H2S began when an experimental gas injection well pipe connection ruptured.  As a result of this small leak, nine people lost their lives.  Some of the victims were actually asleep and were wakened by the “rotten egg” stench of hydrogen sulfide.  They attempted to escape, but unfortunately, it was too late.

Another example highlighting the dangers of hydrogen sulfide was its use as a weapon during World War I.  Although it was not considered to be an ideal war gas, since other gases were in short supply, the British Army used H2S on two occasions in 1916.

H2S Safety Training A Must for Those Who Could Encounter Hydrogen Sulfide

If you work in a workplace that has potential exposure to hydrogen sulfide, you must receive safety training to know how to work safely around it.  This may include emergency response, what kind of personal protective equipment to wear, or just general awareness to areas of concern.

The Hydrogen Sulfide Safety (H2S Safety) Online Course develops workers’ awareness of the hazards of hydrogen sulfide, detection and monitoring methods, and emergency planning and response requirements. Employees who complete this course are better prepared to recognize the symptoms and effects of H2S exposure and protect themselves and co-workers on the job.  

Tags: H2S, hazardous materials, hydrogen sulfide, safety training, workplace safety

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