Crowcon - Detecting Gas Saving Lives
26 November 2015
Hydrogen Sulphide Hazards

Next in our series of short videos is our hydrogen sulphide detection factoid.

Where is H2S found?

Hydrogen sulphide is a significant danger to workers in many industries. It is a by-product of industrial processes, such as petroleum refining, mining, paper mills, and iron smelting. It is also a common product of the biodegradation of organic matter; pockets of H2S can collect in rotting vegetation, or sewage itself, and be released when disturbed.

Hydrogen Sulphide is commonly associated with the refining of crude oil and processing of “soured” natural gas. However, workers in sewerage and waste water plants and pipework can be overcome by H2S, with fatal consequences. Farmers are often unaware of this real danger when entering to inspect an empty slurry tank. The slurry may have been removed, but the gas could still be present.

How is it dangerous?

  • Heavier than air – H2S sinks to the floor and can accumulate in shafts, tunnels, trenches or floor-level ducting.
  • Deadens the sense of smell – Smelling of rotten eggs, the pungent odour of H2S is very noticeable, at first. However, the gas quickly deadens the sense of smell, giving the false impression that the gas has dispersed. Unaware of the persisting danger, someone may continue to work, failing to take adequate precautions against the toxic risk.
  • Dangerous to health – Its high toxicity is the main danger of H2S. Prolonged exposure to 2-5 parts per million (ppm) H2S can cause nausea and headaches, and bring tears to the eyes. At 20ppm, symptoms include fatigue, headaches, irritability, dizziness and impaired memory. Severity of symptoms increase with concentration through coughing, conjunctivitis, olfactory paralysis (loss of sense of smell), collapse and rapid unconsciousness.
  • Instant death – Exposure at higher levels can result in death almost instantaneously. Prolonged exposure to low levels of H2S may cause chronic illness or can also kill. Because of this, many gas monitors will have both instantaneous and TWA (Time-Weighted Average) alerts.
  • Flammable – Hydrogen sulphide is flammable in high concentrations and explosive. In addition, the gas burns and produces other toxic vapors and gases, such as sulfur dioxide.

Protection against H2S

Before entering areas where hydrogen sulphide may be present:

  1. the air must be tested for hydrogen sulphide using gas detection equipment. A multigas detector can test for the presence and concentration of H2S.
  2. If H2S is present, the space must be ventilated continually to remove the gas.  Fire and explosion precautions may be necessary.
  3. If the gas cannot be removed, the person entering the space must use appropriate personal protective equipment, including respiratory equipment and a gas detector.

To find out more about the dangers of Hydrogen Sulphide, read our previous Blog – Hydrogen Sulphide: toxic and deadly

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