What is the problem

This is a very toxic gas (like cyanide) and can cause rapid ‘knockdown’ and death.

Hydrogen sulphide is a potential hazard in tanneries, tanning abattoirs, mining, metal processing, the brewing and fishing industries as well as oil drilling or refining and the chemical, pulp and paper industries.

Other sources include industrial waste, facilities for domestic animals, sewers, natural and volcanic gas, and some hot springs (including the Rotorua thermal region). Confined spaces can increase accumulation and be rapidly fatal.

At low levels, complaints relate to odour, eye or respiratory tract irritation, nausea and headache. Around 250 ppm and above for a minute or more can cause severe breathing depression, fluid in the lungs, depressed circulation, and seizures. Rapid unconsciousness and fatalities can occur at over 700 ppm.

The odour (of rotten eggs) can be detected at low levels (under 1 ppm) though in some is not recognised until 1 to 10 ppm. However olfactory fatigue (i.e you can’t smell it any longer) occurs at about 50 ppm, and can develop within 10 minutes at about 100 ppm. This has obvious serious consequences.

Prolonged exposure can occur if disappearance of odour is mistaken for the dissipation of the gas.

Problem assessment

Hazardous situations include opening doors of pelt processing drums, which has resulted in collapse, coma, and convulsions. Mixing of sodium, calcium or other sulfides with acidic solutions can generate the gas. Agitation of solutions containing hydrogen sulfide may dramatically increase its air level.

Meters are available that indicate hydrogen sulphide concentrations in the air. Often these combine a ‘low oxygen’ warning feature.

Control measures

  • Confirmation of the atmosphere before entry to areas of known or suspected hazard (including confined spaces such as manure pits and sewers) is essential.
  • Where levels are elevated or unknown, use air supply (NOT air purifying) respirators, with sufficient supply taking into account the time required for exiting confined spaces.
  • Wear personal alarms.
  • Provide emergency rescue arrangements – if the prior risk assessment shows that the hydrogen sulphide levels in a confined space can rise.
  • Do not attempt initial rescue unless wearing adequate respiratory protection. Self-contained breathing apparatus (SCBA) is indicated for poorly ventilated, enclosed areas and/or when the gas concentration is unknown. A positive pressure airline respirator is satisfactory under other circumstances.
  • Rescuers should have secure escape routes, safety harnesses and lines, and be observed by other (similarly protected) personnel, outside the area (‘buddy system’).

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