Hydrogen sulphide (H2S) can be found in many environments and industries and its toxicity can arise from both direct contact or as the chemical enters the bloodstream. At high levels of toxicity H2S can have severe side effects including death. 

H2S is a highly flammable, colourless, and toxic gas found naturally in sewage, swamps, manure gas, hot springs, and the anerobic digestion of organics. H2S is a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous system is most affected.

Low-level exposure

Exposure to lower concentrations can result in eye irritation, a sore throat and cough, nausea, shortness of breath, and fluid in the lungs (pulmonary edema).

Long-term, low-level exposure may result in fatigue, loss of appetite, headaches, irritability, poor memory, and dizziness. More importantly continuous exposure can compromise you sensory ability to identify H2S at elevated concentrations.

High-level exposure

Short-term, high-level exposure can induce immediate collapse, with loss of breathing and a high probability of death. If death does not occur, high exposure to hydrogen sulfide can lead to cortical pseudo laminar necrosis, degeneration of the basal ganglia and cerebral edema.

Australian Regulations

Safe Work Australia is currently evaluating the Workplace exposure standards for airborne contaminants to ensure they are based on the highest quality, contemporary evidence and supported by a rigorous scientific approach.

One of the key airborne contaminates that is currently under review is that of Hydrogen Sulphide Gas. As of 2021 the TWA (Time Weighted Average) exposure limits for H2S is 10ppm. However, as of February 2022 this value has been amended to just 1ppm with a three year compliance period. For further information please visit:

Exposure thresholds

  • 00047 ppm or 0.47 ppb is the odour threshold, the point at which 50% of a human panel can detect the presence of an odour without being able to identify it.
  • 10–20 ppm is the borderline concentration for eye irritation.
  • 50–100 ppm leads to eye damage.
  • At 100–150 ppm the olfactory nerve is paralysed after a few inhalations, and the sense of smell disappears, often together with awareness of danger.
  • 320–530 ppm leads to pulmonary edema with the possibility of death.
  • 530–1000 ppm causes strong stimulation of the central nervous system and rapid breathing, leading to loss of breathing.
  • 800 ppm is the lethal concentration for 50% of humans for 5 minutes’ exposure.
  • Concentrations over 1000 ppm cause immediate collapse with loss of breathing, even after inhalation of a single breath.

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