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Working with Hydrogen Sulfide

By James O'Dwyer
Published: December 13, 2017 | Last updated: January 15, 2019 12:03:04
Presented by PEC Safety
Key Takeaways

Hydrogen sulfide exposure can be fatal, but adhering to permissible exposure levels will ensure your workers' safety.

Source: Claffra / iStock

Hydrogen sulfide (H2S) is an extremely dangerous chemical compound that can damage buildings and materials (because of its high flammability) and cause lasting injuries when inhaled, which can sometimes prove fatal. In fact, research suggests that hydrogen sulfide is the number one cause of workplace gas inhalation deaths in the United States.

Given these risks, proper training is critical for any employee who may work with or near H2S.

A Widespread Chemical

Hydrogen sulfide production and use is not restricted to a single industry. It is a byproduct of a wide range of operations, including:

  • Metals and mining
  • Oil and gas
  • Pulp and paper processing

The chemical also tends to fill small, enclosed spaces, meaning that sewage and utility workers are also at risk of inhaling deadly concentrations of it.

Its presence at high percentages in manure also makes it a risk for agricultural workers.

Effects of Hydrogen Sulfide Exposure

Hydrogen sulfide primarily harms the human body when it is inhaled. At low levels of exposure, the symptoms can be relatively mild and could lead to nausea, headache, or watering eyes.

As exposure levels increase (either in concentration in parts per million or the length of time spent exposed) the severity of the symptoms may worsen correspondingly. More severe symptoms include:

  • Bronchial and throat irritation
  • Coughing
  • Changes in mental state

Ultimately, higher levels of exposure may result in paralysis and death.

Although the greatest dangers are associated with inhalation, there may also be risks tied to liquid hydrogen sulfide. Liquid H2S can, for instance, cause a severe form of frostbite when it comes into contact with the skin. Appropriate precautions are required when working with the chemical in its liquid form.

Regulatory Requirements

OSHA has put in place stringent measures to protect employees from the risks of H2S. These requirements supplement OSHA's stipulation that exposure to hazardous or toxic substances shall not exceed 20 parts per million in any industry (and some industries, such as construction, have even lower ceilings on toxic chemical exposure). OSHA guidelines also note that if there is more than 1,500 pounds of hydrogen sulfide in any one location, there is a significant risk of a catastrophic event occurring (for related reading, see When Safety Leadership Failed: Lessons Learned from Major Disasters).

Many of the additional requirements are focused on sampling and monitoring air quality and ensuring that employees have appropriate respiratory and personal protection equipment.

Sampling and Monitoring

Sampling and monitoring air quality serves multiple purposes. First, it allows employers to identify when air quality reaches potentially unsafe levels and to take steps accordingly. But, second, it also serves a long-term purpose. By identifying high levels of hydrogen sulfide, the company can also more effectively track its source and take proactive steps to control the hazard.


For the sampling and testing results to be meaningful, the tests must be carried out by a qualified person using appropriate testing equipment. Depending on the industry and the types of spaces being tested, different types of equipment may be needed, such as:

  • Electronic meters
  • Detector tubes
  • Direct reading gas monitors
  • Explosion meters

When it comes to H2S safety, information is power. Any step you can take to acquire high quality information is worth your while.

Control Measures

Ideally, the hydrogen sulfide problem can be mitigated to zero. However, this is not feasible in every industry or may entail unreasonably high costs. In these cases, employers should impose appropriate engineering and administrative controls.

Installing a state of the art, corrosion- and explosion-proof exhaust and ventilation system is an effective engineering control measure. But these equipment upgrades should be combined with administrative steps, such as workplace safety programs that far exceed OSHA minimums, which are set across industries and may not be enough for every workplace, and educational and training initiatives. Trained workers need to be familiar with emergency plans and relevant first aid procedures.

A workplace safety program that addresses H2S exposure will have two distinct components. The first will be focused on appropriate respiratory and protective equipment. Not only should employees be provided with the right gear, but they must know how to correctly wear and use it. For lower levels of H2S (at or below 100 parts per million), air purifying respirators that offers eye protection and is designed to protect against hydrogen sulfide is adequate. For higher concentrations, a self-contained breathing apparatus (SCBA) with full face pressure will be required.


Hydrogen sulfide is a serious and potentially deadly concern across a wide range of industries. But by complying with, or exceeding, OSHA regulations, employers can take important steps to keep their employees as safe as possible.


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Written by James O'Dwyer | Master Instructor

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With over 20 years invested in safety and training, James O’Dwyer’s professional background reads like an industry dream: 18 years of QHSE experience, 10 years of international E&P and mining-related field experience, and he served as the Royal Canadian Mounted Police Missing Women’s Taskforce HSE for Canada’s largest crime scene. Currently, James is a Master PEC Instructor and part of the company’s Regulatory Outreach Business Development Team. With such dedication to safety and training, James works to continually develop professional networks to help implement partnerships between industry and professional trainers throughout the country.

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