Ever smelled a rotten egg?
Congratulations, you’ve encountered hydrogen sulfide. Sometimes called sour gas, sewer gas, swamp gas, manure gas, or H2S, it’s a common by-product of waste breakdown.
For the general public, it’s just the source of a bad smell. It’s why it smells bad when you pass gas. It’s what makes sewage and manure stink.
But for some workers, it’s a source of serious danger. In significant amounts, hydrogen sulfide can cause severe health problems and even death. In fact, according to the Bureau of Labor Statistics, it killed 60 people between 2001 and 2010.
But what are the dangers of hydrogen sulfide? Who is at risk of toxic exposure? And how do we keep them safe?
What Are the Exposure Risks of Hydrogen Sulfide?
In addition to being highly flammable, hydrogen sulfide is toxic when inhaled.
Low Exposure Symptoms
Hydrogen sulfide can trigger irritation of the eyes and airways at low concentrations. Prolonged exposure from 2 to 10 ppm can lead to:
- Eye irritation
- Trouble sleeping
- Difficulty breathing for asthmatics
At 20 ppm, you can expect to add:
- Loss of appetite
- Memory problems
Moderate Exposure Symptoms
Moderate exposure is more serious. Above 50 ppm, conjunctivitis and respiratory tract irritation occur even in healthy adults, given enough time.
At 100 ppm, you’ll experience drowsiness and trouble breathing after 15-30 minutes. Two full days of exposure can be deadly. Hydrogen sulfide no longer has a scent at this level, so only equipment can provide an exposure warning.
At the higher end of moderate, fluid will start to build up in the lungs.
High Exposure Symptoms
High concentrations of hydrogen sulfide are lethal. Above 500 ppm, most people will collapse within five minutes. They’ll die within the hour unless they’re evacuated. Over 700 ppm, people will fall unconscious after one or two breaths and die within minutes. At 1000 ppm, death is almost instantaneous.
What Puts You at Risk of Hydrogen Sulfide Poisoning?
Hydrogen sulfide occurs naturally in crude petroleum and natural gas. It’s also produced as bacteria break down organic material. Since it’s heavier than normal air, it sinks into low-lying areas and collects in closed, poorly ventilated spaces.
This means you’re at risk for exposure if you:
- work inside confined spaces like manholes, sewer lines, pits, or basements
- are involved in the drilling or refining of petroleum and natural gas
- handle, treat or store waste (including wastewater and manure)
Several manufacturing processes also put workers at risk for hydrogen sulfide poisoning.
How can we control exposure to it?
OSHA has set parameters for industries with occupational exposure to hydrogen sulfide gas. A permissible exposure limit (PEL) has been set in place at ten parts per million (ppm) for an eight-hour shift.
We can control exposure to hydrogen sulfide with the use of:
- ventilation systems that eliminate gas from work areas
- special safety training for workers at risk of hydrogen sulfide exposure
- atmospheric testing and monitoring equipment
- personal protective equipment (PPE)
At or above 100 ppm, OSHA requires the use of self-contained breathing apparatuses on all workers. Below that, air-purifying respirators may be used.
Occupational exposure to hydrogen sulfide is one of the primary causes of death when working in confined spaces. Learn how to protect yourself properly with confined space training, HAZWOPER training, or hydrogen sulfide awareness training, whichever is best suited for your job.