Geothermal Gases

Our most prevalent geothermal gases

Hydrogen Sulfide (also known as H2S, sewer gas, swamp gas, stink damp, and sour damp) is a colourless gas known for its pungent 'rotten egg' odour at low concentrations. At high concentrations H2S has no smell.

Carbon Dioxide (also known as CO2) is a colourless, odourless gas.

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H2S and CO2 are heavier than air and can accumulate in low lying or unventilated areas. They are fast-acting gases, impacting many systems within the body.

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The health effects of H2S and CO2 depend on how much you have been exposed to. Extreme exposure to both gases can be fatal, mild exposure to both gases can cause some respiratory difficulty. The mild symptoms of CO2 are very similar to that of H2S.

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Where you might find H2S and CO2

H2S and CO2 are naturally occurring within the steamfield reservoir and brought to surface saturated within the steam phase.

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As the pressure and temperature drops in steam, the steam becomes oversaturated with H2S, and CO2 and is released into the atmosphere.

Remember, if steam Is present so will H2S and CO2 in varying concentrations.

Within the geothermal process non condensable gases (NCG'S) including H2S and CO2 are collected and discharged through high level stacks then dispersed and diluted into safe concentrations.

Locations where you may encounter raised levels of H2S and CO2:

• vents or drains.

• pits, cellars, and cableways.

• adjacent to NCG handling equipment.

• ponds and low-lying depressions in the ground.

• unventilated or poorly ventilated compartments.

• fumaroles.

• confined spaces

• a failure of machinery seals or pipework may release H2S and CO2 into the atmosphere.

Remember H2S and CO2 will always be present at various levels within the geothermal environment.

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During normal operations H2S and CO2 Is released at known locations (stacks, vents and drains).

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When changes occur in the steam field reservoir, both naturally and intentionally, levels of H2S and CO2 can Increase or decrease without warning.

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When carrying out maintenance tasks accumulated H2S, and CO2 may be disturbed and released outside of the process.

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Atmospheric conditions, including wind direction and ambient temperature changes, can affect dispersion of gases.

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What controls do I need to consider?

Prior to accessing geothermal operational sites, you MUST identify hazards. Information is available from:

• relevant hazard registers

• temporary / unusual hazard boards

• Contact supervisors, nominated supervisors or operational staff.

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Areas requiring the use of personal gas monitors are clearly identified on our operational geothermal sites through signage. Where a dedicated person MUST be assigned to monitor gas levels, you MUST either carry a gas detector or work within a gas monitored area.

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When accessing geothermal operational areas:

• you MUST be trained and competent in the use of the specific gas detectors being used or be supervised

• you MUST identify potential sources of H2S or CO2

• you MUST establish and maintain clear access and egress to the work area.

When completing hazard IDs or risk assessments, the presence of H2S and CO2 MUST be considered.

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It’s YOUR CALL on the requirement for these additional controls:

• establish an evacuation / muster location, ensure that your chosen location is upwind of the potential gas source

• maintain a record of personnel working within the work area and make it available at the evacuation / muster location

• consider placing a windsock in a visible location when working outside.

All visitors to site MUST be made aware of the hazards.

If there is a requirement for the use of SCBA, location / task specific work plans MUST be approved.