A Legionella Risk Assessment (LRA) is a systematic examination of a building’s water systems. This process is foundational to water safety management in non-domestic and large residential properties. The assessment aims to minimize the risk of human exposure to contaminated water aerosols, which can cause severe respiratory illness. The LRA establishes a framework for ongoing control and regulatory compliance.
Understanding the Legionella Threat
Legionella is a genus of naturally occurring bacteria found in freshwater environments like lakes and streams. Legionella pneumophila causes Legionnaires’ disease, a severe form of pneumonia, and Pontiac fever, a milder, flu-like illness. The bacteria thrive when water temperatures are typically between 20°C (68°F) and 45°C (113°F).
The risk increases when water systems allow the bacteria to multiply and then aerosolize. Transmission occurs when people inhale tiny water droplets or mist contaminated with the bacteria. Common sources of these aerosols include cooling towers, showers, decorative fountains, and hot tubs. Sediment, scale, or biofilm provides nutrients and protection, encouraging bacterial growth within the water system.
Mandatory Requirements and Applicability
Legal mandates place the responsibility for conducting an LRA on the duty holder, including building owners, landlords, and facility managers. These individuals are obligated to assess the risks posed by their water systems to employees, residents, visitors, and the public. This necessity is rooted in health and safety regulations that require a proactive approach to managing hazardous substances.
An LRA is required for any premises where water is stored or re-circulated, creating a potential risk. This broad applicability covers commercial buildings, hospitals, hotels, and residential blocks with complex plumbing. Systems of particular concern include cooling towers, evaporative condensers, hot and cold water storage tanks, and spa pools. Infrequently used outlets, where water can stagnate, must also be included in the assessment scope.
Core Steps of the Risk Assessment
The assessment process is undertaken by a competent person who systematically evaluates the entire water infrastructure.
System Survey and Mapping
The initial phase is a comprehensive survey to map all water assets, including storage tanks, calorifiers, pipework, and terminal fittings. This establishes a baseline understanding of how water flows and where it might be stored or recirculated.
Hazard Identification
The assessor identifies conditions that encourage Legionella growth. This includes measuring water temperatures to find zones between 20°C and 45°C, where the bacteria multiply. The assessment also looks for physical deficiencies, such as areas of stagnation (“dead legs”), corrosion, scale, and sludge that act as nutrient sources.
Risk Rating and Documentation
Risk rating evaluates the likelihood of exposure to contaminated aerosols and the severity of consequences. This rating considers the vulnerability of occupants, such as the elderly or those with compromised immune systems. Finally, the assessor documents all findings and creates a Written Scheme, which outlines the control measures proposed to manage the identified risks.
Implementing Control and Review Cycles
The Written Scheme serves as the blueprint for an ongoing risk management program. Immediate action involves implementing physical control measures to disrupt the bacteria’s growth environment. This includes maintaining hot water above 50°C and cold water below 20°C to inhibit multiplication.
Control Measures
System modifications are often necessary, such as removing redundant pipework or “dead legs” to prevent water stagnation. Regular maintenance includes cleaning, descaling, and using chemical disinfection or biocides to control bacterial levels. A continuous monitoring schedule is established to routinely check and record water temperatures, disinfectant levels, and system condition.
Review Cycle
The LRA is the starting point of a dynamic control cycle, not a singular event. The assessment must be reviewed regularly, typically every two years, or immediately whenever a significant system change occurs. Triggers for an earlier review include building refurbishment, changes in the water system layout, or a failure in the existing control measures.