Legionnaires' disease is a potentially fatal form of pneumonia caused by Legionella bacteria. These bacteria thrive in water systems between 20-45 degrees Celsius and can be inhaled through water droplets. Employers and building owners have a legal duty to assess and control Legionella risks.

Legal Requirements

Under the Health and Safety at Work Act 1974 and Control of Substances Hazardous to Health Regulations 2002 (COSHH), duty holders must:

Identify and assess sources of Legionella risk
Prepare a scheme to prevent or control risk
Implement and manage the scheme
Keep records
Appoint a competent responsible person

High-Risk Water Systems

Systems that may require Legionella risk assessment include:

Hot and cold water systems
Cooling towers and evaporative condensers
Spa pools and hot tubs
Humidifiers and air washers
Dental equipment
Vehicle wash systems
Indoor fountains and water features

Risk Factors

Conditions that increase Legionella risk:

Water temperature between 20-45 degrees Celsius
Stagnation (dead legs, infrequently used outlets)
Biofilm and scale deposits
Nutrients for bacterial growth (rust, sludge, organic matter)
Aerosol generation (showers, spray taps, cooling towers)

Who is at Risk?

While anyone can contract Legionnaires' disease, higher risk groups include:

People over 45 years old
Smokers and heavy drinkers
People with chronic respiratory or kidney disease
Those with weakened immune systems

Control Measures

Key control measures include:

Temperature Control

Store hot water at 60 degrees Celsius or above
Distribute hot water at 50 degrees Celsius or above
Keep cold water below 20 degrees Celsius

System Management

Avoid stagnation - flush little-used outlets weekly
Remove dead legs and redundant pipework
Clean and disinfect systems regularly
Maintain accurate records

Monitoring

Monthly temperature checks at representative outlets
Quarterly checks of calorifier temperatures
Visual inspections of tanks and calorifiers
Water sampling where appropriate