Hydrogen sulfide (H₂S) gas can be fatal at high concentrations. But even low concentrations can cause health issues, particularly with prolonged exposure. So how can you help protect workers and minimize downtime? Get answers to some of the most common questions about H₂S and find out how connected gas detection solutions can help enhance worker safety and drive productivity.

What is H₂S gas?

Hydrogen sulfide is a highly flammable, toxic, and corrosive gas found in several industries including oil and gas, wastewater, and chemical processing. It’s sometimes called ‘sour gas’, ‘sewer gas’ or ‘stink damp’ because of the way it smells like rotten eggs. However, H₂S cannot reliably be detected by smell as it quickly deadens the sense of smell (a process known as ‘olfactory desensitization or fatigue’).

How dangerous is H₂S?

Exposure to high levels of H₂S can be fatal, leading to loss of breathing, coma, seizures, and death. It’s the second most common cause of fatal gas inhalation exposure in the workplace, second only to carbon monoxide.¹

But H₂S can also be harmful at low concentration levels, causing headaches, dizziness, nausea, breathing difficulties and a sore throat. These health impacts can become more serious with prolonged exposure.

NIOSH and OSHA Guidelines for H₂S Exposure Limits

The health impacts of H₂S depend on how much is inhaled and for how long.

The recommended exposure limit set by the National Institute for Occupational Safety and Health (NIOSH) for ten minutes is 10 ppm.²

OSHA identifies Permissible Exposure Limits (PELs) for H₂S based on industry, outlining the highest acceptable exposure levels during an 8-hour shift:³

• General Industry Ceiling Limit: 20 ppm
• General Industry Peak Limit: 50 ppm (OSHA notes that this limit is in cases where there is no other exposure during the shift)
• Construction 8-hour limit: 10 ppm
• Shipyard 8-hour limit: 10 ppm

However, some states have developed ambient air standards for H₂S well below OSHA and NIOSH standards due to concerns about health risks from chronic exposure.⁴

Which industries commonly face H₂S concerns?

H₂S creates safety challenges for many industries. But some industries are more likely to be affected. These include:

Oil, Gas & Petrochemical (OGP)

OGP facilities handle raw ‘sour’ gas and oil which are naturally high in H₂S. Extraction and refining processes release H₂S, which may accumulate in confined, poorly ventilated spaces including processing units, pipelines, and storage tanks. Closed systems with high-pressure conditions amplify the risks for workers.

Wastewater Management

Wastewater facilities such as closed pipelines and sludge tanks have low oxygen levels, providing the ideal conditions for H₂S buildup. This is because sulfate-reducing bacteria which break down organic material and produce H₂Sas a byproduct thrive in anaerobic (low-oxygen) conditions.

One of the key risks for wastewater workers is entering confined spaces such as tanks and sewer lines. For many wastewater management businesses, real-time monitoring of gas levels is considered a must-have.

Steel production

The steel industry’s use of high-temperature processes and sulfur-rich materials can lead to the release of H₂S, creating hazards for workers. Confined, poorly ventilated spaces and desulfurization units can pose unique risks.

How Connected Gas Detection Can Help Mitigate H₂S Risks

Connected gas detection solutions, such as the ALTAIR io™ 4 Gas Detection Wearable and Grid software, can help provide real-time visibility of workers and worksites, giving safety managers access to gas readings, worker-initiated exposure alarms, and the ability to send evacuation notices. Since early warning can help organizations stay ahead of potential risks, ALTAIR io 4 devices are designed to detect even subtle increases in H₂S concentration levels at a resolution as low as 0.1 ppm. With the fleet management and configuration capabilities of ALTAIR io 4 devices and Grid, organizations have the ability to customize to their own SOPs; for example, ALTAIR io 4 devices may be configured for low concentration H₂S detection starting at either the default of 0.3 ppm or as low as 0.0 ppm.*

*The default configuration for low-concentration H₂S detection on the ALTAIR io 4 connected gas detector starts at 0.3 ppm, but customers may choose to configure the device to detect H₂S starting at 0.0 ppm (in increments of 0.1 ppm).

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Sources:

1. Guidotti TL, 2010. Hydrogen sulfide: Advances in understanding human toxicity. Int. J. Toxicol 29, 569–581 
2. https://www.cdc.gov/niosh/npg/npgd0337.html
3. https://www.osha.gov/hydrogen-sulfide/hazards
4. https://ohsonline.com/articles/2007/10/human-health-effects-from-exposure-to-lowlevel-concentrations-of-hydrogen-sulfide.aspx