What is Hydrogen Sulphide and How is it Detected?
Hydrogen Sulphide (H2S) is a colourless, flammable, toxic gas with a distinctive rotten egg odour at low concentrations. It is known to cause metal corrosion as well as health effects in humans.
Sources of H2S
Waste Water Treatment Plants – Sources of Hydrogen Sulphide
In Christchurch and Lower Hutt residents have been experiencing strong offensive odours. These odours are from the waste water treatment plants. This odour can make people sick and revert to keeping windows closed.
Hazards from Odour
The odour threshold for H2S is 0.04 – 1 ppb. This means at very low levels; individuals will detect a rotten egg odour.
The New Zealand Air Quality Guideline for H2S is 7 µg/m3 (4.94 ppb) per hour. This guideline level is based on odour nuisance. At 3000-5000 ppb odour is considered strong.
At 100-200ppm your ability to smell H2S odour dissipates. (paralysis of the olfactory apparatus) This is an extreme hazard as often people aren’t aware they are been exposed to high concentrations of the gas.
Having any cold or flu-like symptoms will affect an individual’s ability to smell the gas.
There is also a hazard for workers from repeated continuous exposure. An individual’s sensitivity to the gas is reduced through this type of exposure.
The Californian EPA has a guideline limit of 42 µg/m3 (29 ppb) for short term exposure – 8 hours and 10 µg/ m3 (7 ppb) for long term exposure – one year.
Natural
H2S occurs naturally in geothermal areas, sewers, oil and gas wells.
It is formed under oxygen sparse conditions when organic material and sulphate is present. H2S is produced by bacterial action during the decay of plant and animal protein (Cooper et al, 1976).
The natural background or urban air levels of H2S can be difficult to measure. They are estimated to be below 0.15 µg/m3 (0.1 ppb). In Rotorua, New Zealand 1 hour mean concentrations have been reported up to 2000 µg/m3 (1400 ppb) (Thom and Douglas, 1976).
Man-Made
H2S can be produced as a by-product of numerous industrial processes. This includes:
- Manure and offal pits,
- Removal of hair from hides in tanneries,
- Drilling and civil works in geothermal areas,
- Treatment of toxic wastes,
- Production and refining of oil and gases,
- Pulp and paper manufacturing processes, and
- Sewer, tanks and sewage treatment plants.
Risk of Exposure
Due to its chemical properties, H2S can be difficult to detect. H2S gas is heavier than air, and may travel along the ground making confined space work extremely dangerous in industries with H2S as a by-product.
An individual can be exposed to H2S via inhalation. This is then absorbed through the lungs into the bloodstream.
H2S does not accumulate in the body from repeated exposure however, exposure to H2S above 100 ppm is immediately dangerous to health and life
Health Effects at Specified Levels
| Concentration (ppb) | Observations and Health Effects |
| <1 000 | Most people smell a rotten egg odour |
| 10 000-20 000 | Threshold for eye irritation |
| 20 000-150 000 | Headache, nausea, respiratory irritation, pain in legs |
| 150 000-200 000 | Sense of smell is blocked (olfactory fatigue) |
| 200 000-500 000 | Major respiratory irritation, vertigo, vomiting. Death can occur within 1-4 hours of exposure |
| Above 500 000 | Muscular spasm-twitching convulsions, immediate loss of consciousness, rapid death. |
If a worker survives a severe acute exposure, they may still have long-term health effects. This includes:
- Irritability
- Anxiety
- Fatigue
- Impaired memory
- Impaired nervous system
- Permanent respiratory distress
What can K2 Environmental Offer?
K2 Environmental Ltd specializes in air quality assessment and testing. Our expert team offers comprehensive services to help you protect the health and safety of your workforce. Here’s how we can assist:
- Ambient Boundary Monitoring. We measure H2S levels to ensure compliance of safety standards and resource consents.
- Workplace risk assessments – this can include air sampling for hydrogen sulphide as part of the assessment of risk to health.
- Liberation Source Assessments. Our team identifies any ambient source of H2S through electronic equipment and odour surveys.
- Stack Emission Testing. We are IANZ accredited for air discharge sampling of hydrogen sulphide, total reduced sulphur, sulphur dioxide, and sulphur trioxide and air discharge analysis of sulphur dioxide/sulphur trioxide and total reduced sulphur.