Manitoba has seen recent serious incidents involving worker exposures to hydrogen sulfide (H₂S). H₂S is a flammable, highly toxic gas with a characteristic rotten‑egg odour at low concentrations. H₂S is produced when organic matter decomposes in the absence of oxygen, which can occur in both industrial and non-industrial settings.
Common locations where H₂S may be present include:
H₂S is heavier than air, allowing it to settle and accumulate in pits, trenches, crawlspaces, sumps, basements and other depressions—even outdoors.
Two recent serious incidents illustrate the unpredictable ways H₂S can accumulate and be released.
Workers moving decomposing hay bales disturbed an area where H₂S had developed beneath the bales. When the bales were shifted, the trapped gas was suddenly released, exposing workers to harmful concentrations, despite being outdoors.
Key takeaway:H₂S can build up in sheltered, low‑lying pockets, even in open-air environments, whenever decomposing organic material is present.
At a residential plumbing worksite, a worker poured two different drain clearing chemicals into a plugged sewer drain. The chemicals produced an exothermic reaction that released an H₂S pocket from the drain. The reaction exposed the worker to a high concentration of H₂S.
Key takeaway:Routine plumbing tasks can become high‑risk when blockages in sewer systems may cause H₂S pockets to form.
H₂S exposure symptoms depend on concentration and duration:
H₂S exposure level in parts per million (ppm)
Potential signs or health effects
Greater than 1 ppm
Smell of rotten eggs.
20-50 ppm
Irritation of eyes, nose or throat.
100-150 ppm
Severe irritation of eyes, nose or throat, loss of smell. Exposure over a period of eight hours or more may be fatal.
200-300 ppm
Headaches and drowsiness. Exposure for hours may cause lungs to fill with fluid.
300-500 ppm
May cause unconsciousness and death in one to four hours.
500-700 ppm
One hour at this level may be fatal.
> 700 ppm
May be immediately fatal.
As per Part 36 of the Workplace Safety and Health Regulation (WSH Regulation), workers should be trained on safe work procedures, including the hazards of H2S, and direct reading monitoring. Workers should be educated on the sources of H2S, the risks and symptoms associated with H2S and the actions to take if H2S is encountered.
As per Part 19.2 of the WSH Regulation, the fire hazard from H2S shall be assessed, safe work procedures must be developed and implemented and workers educated and trained.
As per Part 35.3 of the WSH Regulation, educate and train workers on the hazardous product (H2S) that they may encounter, the Safety Data Sheet information, procedures for working with the hazardous product and procedures to be followed in case of an emergency involving the hazardous product.
As per Part 2.7(1) of the WSH Regulation, an employer must immediately notify Workplace Safety and Health when there is an uncontrolled release of a hazardous substance (H2S).
Part 9 of the WSH Regulation requires workplaces to establish procedures for when workers are working alone.
As per Part 6 of the WSH Regulation, employers providing workers with SCBA shall provide workers with training and education on using it as well as ensuring it is sufficiently charged and has a minimum of 30 minutes of air.
If you have questions about this topic, contact the SAFE Work Manitoba division.
The Workers Compensation Board of Manitoba serves workers and employers through a no-fault insurance system integral to the Manitoba economy. Funded collectively by employers, the WCB promotes safe and healthy workplaces, facilitates recovery and return to work, delivers compassionate and supportive compensation services to workers and employers, and ensures responsible stewardship of Manitoba's workers' compensation system.
