WWT/Specific Hazards/TBT-WWT-007

Methane and Biogas Hazards

Water & Wastewater Treatment › Specific Hazards › Methane and Biogas Hazards

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Methane is produced by anaerobic decomposition of organic material in sewers, digesters, sludge storage, and landfill sites.
Methane is lighter than air, odourless, colourless, and explosive between 5% and 15% concentration in air.
Biogas from digesters is a mixture of approximately 60% methane and 40% carbon dioxide, with trace hydrogen sulphide.
An explosive methane-air mixture can be ignited by electrical sparks, hot surfaces, static discharge, and naked flames.
Methane displaces oxygen in enclosed spaces, causing asphyxiation without any warning odour or visible sign.
Gas detection equipment must be calibrated and carried by all workers entering areas where methane accumulation is possible.
Confined space entry procedures apply to all structures where methane may be present, including digesters, manholes, and tanks.
ATEX-rated electrical equipment must be used in zones classified as potentially explosive atmospheres due to methane.
Biogas systems including pipework, storage holders, and flare stacks must be maintained to prevent uncontrolled methane release.
Emergency procedures for methane detection must include immediate evacuation and prohibition of all ignition sources.

Explosive atmosphere	Methane between 5% and 15% in air is explosive — a single spark in an enclosed space causes a devastating explosion.
Silent asphyxiant	Methane has no smell, colour, or taste — it displaces oxygen silently, causing unconsciousness and death without warning.
ATEX requirement	Standard electrical equipment can ignite methane — only ATEX-rated equipment is safe in potentially explosive atmospheres.

Don't

Carry a calibrated gas detector in all areas where methane accumulation is possible.
Follow confined space entry procedures for all structures with potential methane risk.
Use only ATEX-rated electrical equipment in zones classified as explosive atmospheres.
Eliminate ignition sources including phones, cameras, and non-ATEX tools in gas zones.
Ventilate enclosed spaces to prevent methane accumulating to explosive concentrations.
Maintain biogas pipework, holders, and flare stacks to prevent uncontrolled releases.
Evacuate immediately if gas detection indicates methane levels approaching the LEL.
Brief all workers on methane hazards and the emergency evacuation procedure.
Monitor continuously — methane levels can change rapidly from zero to explosive.
Ensure rescue equipment is ready before entering any area with methane risk.

DON'T enter areas with potential methane risk without a calibrated gas detector.
DON'T enter manholes, digesters, or tanks without confined space permits and monitoring.
DON'T use standard electrical equipment in areas classified as explosive atmospheres.
DON'T create any ignition source in areas where methane may be present.
DON'T work in enclosed spaces without forced ventilation dispersing any methane.
DON'T neglect maintenance on biogas systems — leaks create explosive hazards.
DON'T remain in an area where methane levels are rising towards the lower explosive limit.
DON'T assume workers understand methane risks — brief them specifically on the hazard.
DON'T rely on a single reading — monitor gas levels continuously throughout the task.
DON'T enter methane risk areas without rescue equipment and a plan at the surface.

See also: Atmospheric Monitoring and Gas Testing | Confined Space Awareness

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