OCC/Welfare/TBT-OCC-015

Legionella Awareness

Occupational Health › Welfare › Legionella Awareness

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Legionella is a bacterium that causes Legionnaires' disease, a severe and sometimes fatal form of pneumonia.
The bacteria thrive in warm water between 20°C and 45°C, especially in stagnant or low-flow conditions.
Construction sites with temporary water supplies, showers, and welfare facilities can harbour legionella.
Cooling towers, hot and cold water systems, and spa pools are common sources of legionella outbreaks.
Infection occurs by inhaling water droplets or mist containing the bacteria — not by drinking contaminated water.
HSG274 and the Approved Code of Practice L8 set out the legal framework for legionella control in the UK.
A legionella risk assessment must be carried out for all water systems that could create an aerosol.
Dead legs, unused outlets, and infrequent flushing allow water to stagnate and bacteria to multiply.
Temperature control is the primary prevention method — hot water above 60°C and cold water below 20°C.
Symptoms include high fever, cough, muscle pain, and breathing difficulty — medical attention is urgent.

Fatal disease	Legionnaires' disease has a mortality rate of approximately 10% — it kills previously healthy adults.
Legal duty	The HSE Approved Code of Practice L8 requires duty holders to assess and control legionella risk in water systems.
Construction risk	Temporary water systems, new installations, and commissioning activities create ideal conditions for legionella growth.

Don't

Carry out a legionella risk assessment for all site water systems producing aerosols
Flush unused water outlets weekly to prevent stagnation in dead legs and low-use areas
Maintain hot water storage at 60°C and distribution above 50°C to kill bacteria
Keep cold water below 20°C and insulate cold pipes away from heat sources
Clean and disinfect temporary water tanks, showers, and welfare water systems regularly
Commission new water systems with a full chlorination and flushing protocol
Record all legionella control actions including temperatures, flushing, and testing dates
Appoint a responsible person to manage legionella controls on site
Seek urgent medical attention for anyone with persistent high fever and cough symptoms
Ensure cooling towers are registered and managed under HSG274 guidance

DON'T allow water to stagnate in unused pipes, dead legs, or temporary tanks
DON'T let hot water storage temperatures drop below 60°C in calorifiers or tanks
DON'T route cold water pipes next to hot pipes or through warm spaces without insulation
DON'T skip weekly flushing of low-use outlets including showers and wash basins
DON'T commission new water systems without chlorination and thorough flushing
DON'T ignore legionella risk on construction sites because the systems are temporary
DON'T allow dirt, debris, or biological material to accumulate in water storage tanks
DON'T use site showers that have not been included in the legionella management plan
DON'T dismiss flu-like symptoms in workers exposed to site water systems — seek medical help
DON'T operate cooling towers without leak detection checks and water treatment programmes

See also: Occupational Health Awareness | Welfare Facilities Standards

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