Hydrogen Sulfide - Frequently Asked Questions (FAQ)

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Hydrogen Sulfide - Frequently Asked Questions

Before answering frequently asked questions about Hydrogen sulfide, it is important to understand it – Hydrogen Sulfide, also known as H2S, sour gas, sewer gas, and sour damp – is a colorless gas that is poisonous, corrosive, and flammable. Although it has a foul odour that resembles rotten eggs, the smell disappears the more you inhale it. Hydrogen sulfide occurs naturally and is released when organic matter decays. It can also be produced during refinement processes involving natural products. In some cases, H2S is released in a liquid known as hydrosulfuric acid.

Those in blue collar industries are the most likely to be exposed to H2S, including those working in:

    Oil & Gas
    • Mining
    • Tanning
    • Pulp and paper processing
    • Rayon manufacturing
    • Farming
    • Sanitation

Because hydrogen sulfide is heavier than air, it can collect in low-lying, enclosed spaces, meaning that any job involving work in confined areas is at risk. Also, jobs in swampy or marshy areas are more at risk of H2S exposure because heat accelerates the decomposition of rotting organic material, speeds up the production of H2S, and increases H2S’ vapor pressure.

There is a chance of H2S exposure even when access to the most dangerous areas is restricted, which is why all employees must be knowledgeable about this toxic gas. Scroll down to learn more about hydrogen sulfide or click on one of these frequently asked questions to see a specific answer.
Frequently Asked Questions About Hydrogen Sulfide:

Why do I need hydrogen sulfide safety training?

Workers who do not know the hazards of H2S are more likely to be harmed by it, and this is why H2S training is critical to employees’ health and safety. Even exposure to low levels of H2S has negative health effects, so workers should know what it is, where it can be found, what equipment to use if it may be present, and what to do if someone is exposed to it.

What are common signs that I have been exposed to hydrogen sulfide?

With low levels of hydrogen sulfide, you will notice the rotten egg smell. You may also experience nausea, soreness, irritation of the eyes or eye spasms, sore nasal passages, a sore throat, a tight chest, a burning sensation in your lungs, headaches, confusion, dizziness, or vomiting. Those with asthma may have difficulty breathing even when the lowest levels of the gas are present. Exposure to hydrosulfuric acid can cause frostbite-like burns on the skin.

With high levels of H2S, the symptoms could appear quickly and with little warning. A worker could become unconscious, after which he or she may continue to experience headaches, a poor attention span, memory loss, or reduced motor function. Another possible outcome is the failure of the respiratory or cardiovascular system. In the most serious cases, the result of a high level of exposure is death.

How much exposure is too much for H2S?

Because the long-term effects of hydrogen sulfide exposure are still not well known, limiting exposure at all times is best.

The concentration of hydrogen sulfide is measured in parts per million (ppm). Our bodies actually produce small amounts of H2S, and a low concentration of it may be present in the background of a worksite. But, once the gas becomes more concentrated (especially in confined spaces), it becomes more lethal.

The level of distinct odor awareness (LOA) for H2S is 0.01 ppm (source). The odour becomes strong when it reaches 2-3 ppm, and this is also when many of the signature symptoms of exposure begin. The longer the exposure, the worse the symptoms and the more likely you are to experience more of them. To see a chart of concentration levels and related symptoms and effects, read Work Safe BC’s Hydrogen Sulfide handout.

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Does hydrogen sulfide cause cancer?

Hydrogen sulfide has not been shown to cause cancer, but scientists continue to study the potential link between H2S and cancer in animals.

Does hydrogen sulfide have long-term health effects?

Although the research on acute exposure to H2S is better known, most sources agree that there could be negative effects on heath after chronic exposure, too. Reported symptoms of long-term exposure include tiredness, dizziness, irritability, headaches, loss of appetite, and problems with memory.

What equipment is useful to reduce exposure to H2S?

Certain tools evaluate hydrogen sulfide levels, and engineering controls such as exhaust ventilation help reduce exposure when the gas cannot be completely eliminated. The levels should be constantly monitored to keep the area safe, and regular preventative maintenance will reduce the risk of leaks.

Hydrogen sulfide personal protective equipment (PPE) is also a critical way to limit hydrogen sulfide exposure. Workers should wear breathing protection, protective clothing, and safety glasses in areas where H2S is present.

Finally, regular safety training and practice with the H2S PPE is important for limiting the risk of exposure and injury. Each employee should know the signs of hydrogen sulfide on the work site, the symptoms of exposure, and the steps to take when exposure occurs.

Can you see or smell hydrogen sulfide?

You cannot see hydrogen sulfide, but it does have a strong odour that resembles rotten eggs. However, H2S blocks your sense of smell in large amounts, which means the odour goes away over time – making it even more dangerous. Do not judge the concentration of H2S in an area based off of the smell.

What should I do if I or a co-worker is exposed to dangerous levels of H2S gas?

Take measures to address the symptoms you or your co-workers are experiencing. Start by getting to fresh air immediately. Oxygen therapy is the best treatment for breathing in H2S gas.

  • If your eyes are itchy, stinging or watery, immediately flush them with lukewarm water for 30 minutes. If your eyes continue to itch, see a doctor as soon as possible.
  • If you touch liquid hydrogen sulfide (hydrosulfuric acid), get medical help immediately. Clothes that have been saturated with hydrosulfuric acid need to be removed, kept away from ignition sources, and left to dry out.

In the most serious cases, it is important to use the proper precautions and PPE when helping others as you wait for emergency services.

  • If you must perform a rescue in an area with high levels of H2S, wear either a self-contained breathing apparatus (SCBA) or a full-face, air-supplied respirator with an escape air bottle before entering the affected area.
  • If you have trouble breathing, begin assisted ventilation using a pocket mask.
  • When no pulse is detected in someone you are trying to help, begin cardiopulmonary resuscitation (CPR).
  • Get all severely affected people to a hospital.

The presence of hydrogen sulfide on a work site may be impossible to eliminate completely, so it is important to train employees about H2S, how to know if it is present, the symptoms and effects of exposure, and what to do if someone does get exposed to it – the health and safety of your organization depends on it.


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