Exposure of workers to hydrogen sulphide gas

Safety Alert | 12/06/2018

This safety alert is for NSW workplaces which may use, generate, store or handle hydrogen sulphide (H2S) gas. It will help them to identify sources of potential exposure and manage risks to health and safety. This is especially important for work in, on or near confined spaces such as tanks, pits, sumps, vessels as well as partially enclosed areas with poor ventilation. Hydrogen sulphide can be produced unintentionally.

Hydrogen sulphide is found during the production and drilling of crude oil and natural gas, in sewers and sewage treatment plants, in swine and manure-handling operations, and in pulp and paper operations. Hydrogen sulphide can be produced by bacterial breakdown (rotting) of organic materials and human and animal waste (e.g. sewage, vegetable waste). It is also found in petroleum refineries, natural gas plants, petrochemical plants, coke oven plants, food processing plants and tanneries.

Key Points

  • Breathing in high levels of hydrogen sulphide gas can kill in minutes.
  • Do not rely on your sense of smell to warn of dangerous levels. You can smell the gas at low levels, but at high levels you cannot smell it. This means it may be too late to escape a contaminated area after it has been entered.
  • The gas is heavier than air and may be released only after sludge or waste is disturbed.
  • Use gas detection equipment to monitor for hydrogen sulphide. If gas is in the air, continually ventilate the space with fresh air.
  • Only enter the space once gas detection equipment has confirmed it is safe to do so.
  • Have the right emergency and personal protective equipment in place; and have the right information and training to use it.
  • Do not attempt to rescue someone without the right safety equipment and training as you could be exposed to the deadly gas.


Recently two workers died at a paper mill, likely due to breathing in high levels of hydrogen sulphide gas from a tank used for containing process water. Uncovered openings allowed the gas to escape and overcome the workers.


Hydrogen sulphide is a flammable, colourless gas that smells like rotten eggs.  People can usually smell it at low levels but lose their ability to smell it at high levels. This is important because you might falsely think it is no longer present, which will increase your risk of exposure. Exposure can cause serious injury, illness or death from fluid on the lungs and the body’s inability to use oxygen. Death can happen almost instantly. Hydrogen sulphide is a highly flammable gas and can be explosive.

Hydrogen sulphide collects in confined spaces and poorly ventilated or enclosed areas such as pits, tanks, vessels, sewer lines, manure pits and manholes and may be released into the air only after any organic matter or sludges have been disturbed e.g. through mixing, stirring, or walking through rotting material.

In the pulp and paper industry hydrogen sulphide may result from cooking processes, acid cleaning equipment and the mixing of acids with process liquors which can produce large volumes of gas, even in open environments. It can also be produced when separate acid and process sewers come together in effluent ponds.

Action required by persons conducting a business or undertaking

  • Eliminate or minimise the risk that hydrogen sulphide can be unintentionally generated or produced e.g. use biocides.
  • Identify any confined spaces or hazardous areas such as tanks (including partially enclosed tanks), pits, sumps and vessels, which may release, produce, store or contain hydrogen sulphide or other hazardous gases.
  • Eliminate the need to enter confined spaces or hazardous areas.
  • Eliminate or manage the risks associated with entering, working in, on, or near a confined space or hazardous area by:
    • ensuring a competent person conducts a risk assessment, including the requirements for gas detection, before anyone enters a confined space
    • ensuring a confined space work entry permit is issued before any person enters the space
    • ensuring the permit lists the measures to control the risks.
  • Review and check the control measures are in place.
  • Provide workers adequate information, instruction, supervision and training on the hazards, control measures, personal protective equipment, entry permits and emergency procedures.
  • Ensure first aid and emergency procedures are in place.
  • Ensure new hazards are not created when introducing or changing processes.
  • Consult with workers on all the above.

Refer to the requirements for hazardous chemicals and confined spaces in the NSW WHS Regulation 2017, the SafeWork NSW Code of Practice on confined spaces and the SafeWork NSW Code of Practice Managing risks of hazardous chemicals in the workplace.

Additional Information

For further information on hazardous chemicals call 13 10 50 or visit www.safework.nsw.gov.au.

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