WWT/Process Areas/TBT-WWT-013

Storm Tank and CSO Safety

Water & Wastewater Treatment › Process Areas › Storm Tank and CSO Safety

Presenter		Project
Location		Date

Storm tanks and combined sewer overflows (CSOs) hold diluted sewage during heavy rainfall events.
These structures present confined space, drowning, and biological hazards to workers.
Water levels can rise rapidly and without warning during rainfall upstream in the catchment.
Hydrogen sulphide (H2S) and methane may be present, particularly after prolonged dry weather.
Surfaces inside storm tanks are often covered in biofilm making them extremely slippery.
Storm tanks may contain debris, sharps, and industrial contaminants from the sewer network.
Entry into storm tanks and CSO chambers requires a confined space permit and rescue plan.
Real-time weather monitoring and flow data should inform risk assessments for these structures.
Workers must be vaccinated against hepatitis A and tetanus before entering sewage-related areas.
Drowning remains the leading cause of fatality in water industry confined space incidents.

Drowning risk	Storm tanks can fill rapidly during rainfall — water levels may rise metres within minutes, trapping workers inside.
Toxic atmosphere	H2S and methane accumulate in enclosed sewage structures and can cause unconsciousness or death within seconds.
Biological hazards	Contact with raw sewage exposes workers to leptospirosis, hepatitis, and other serious infections.
Legal duty	The Confined Spaces Regulations 1997 and CDM 2015 require employers to control these risks with robust safe systems of work.

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See also: Hydrogen Sulphide (H2S) on WwTW | Confined Space Entry Procedures

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