H2S: The Dangers and Some Controls

Hydrogen sulfide (H2S) is a colourless gas well known to have a strong and pungent odour of rotten eggs (at low concentrations) and goes by various nicknames such as sewer gas, swamp gas, and sour gas. It is a naturally occurring gas produced by decaying organic matter, and can be found in sewers, oil and gas deposits, and volcanoes.

H2S Across Industries

h2s monitor H2S is also used or produced in several industries, such as oil and gas, mining, manufacturing, and processing. The gas is heavier than air and can collect in low-lying and enclosed spaces such as; manholes, sewer lines, underground vaults, and storage tanks (above or below ground). It is a highly dangerous gas, even in very low concentrations, which can make working around it extremely dangerous.

According to OSHA, H2S gas is one of the leading causes of workplace gas inhalation deaths.

The Dangers of Exposure

As mentioned above, low concentrations of H2S (<150 ppm) have a strong odour of rotten eggs, which develops into a ‘sickeningly sweet’ smell the higher it gets. Low concentrations of the gas can lead to feelings of nausea, tearing of the eyes, and headaches. Between 100 and 150 ppm, a person will lose their sense of smell due to ‘olfactory fatigue or paralysis’, which makes H2S even more deadly, as some people may think the hazard has passed since they can’t smell it anymore. A concentration of 100 ppm also marks the point that H2S becomes ‘immediately dangerous to life and health’ (IDLH) as defined by the National Institute for Occupational Safety & Health (NIOSH) because your ability to excavate or escape the area starts to become impaired.


Due to the high potential for danger that H2S can present, having controls to eliminate or decrease the risk of H2S gas is extremely important.

Administrative controls involve creating safe work procedures, emergency response plans, and a management plan for H2S gas.

Engineering controls include isolating areas with the potential for H2S exposure and proper ventilation systems to take the gas away.

The final form of control and last line of defense is personal protective equipment (PPE), such as respirators, self-contained breathing apparatus, and H2S monitoring devices.

H2S Monitoring

h2s gas exposure illustration While all of the administrative and engineering controls are extremely important for eliminating the potential for exposure, monitoring for H2S gas stands as one of the most effective ways for workers to protect themselves from the harmful effects of H2S gas. An H2S monitor clips onto a worker’s collar and monitors their ‘breathing zone’. As gas and air pass through the monitor, it analyzes it for any trace of H2S. If it starts to detect any concentration of H2S above a certain threshold, it will begin vibrating and alarming to notify the worker of the danger.

From this point, the worker can then notify everyone else around them, and begin taking the next steps depending on the concentration that is being recorded, whether that is to immediately evacuate the area or don the necessary extra PPE.

In a worst-case scenario, when all the other administrative and engineering controls fail, the personal H2S monitoring device will be the control that can mean the difference between life and death for some workers.

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