Legionnaires' Disease Part 2: Control of Legionella Bacteria in Hot and Cold Water Systems

Publication Year: 2014

This guide is prepared to assist duty holders such as employers, building controllers, and others responsible for health and safety in fulfilling their legal obligations. These obligations include identifying and assessing risk sources, preparing a plan to prevent or control the risk, implementing, managing and monitoring the measures, keeping records related to the measures, and appointing a manager responsible for others.

The guide provides practical information on the legal requirements of relevant legislation such as the Health and Safety at Work Act 1974, the Control of Substances Hazardous to Health Regulations (COSHH) 2002, and the Management of Health and Safety at Work Regulations 1999.

Contents

  • Introduction
  • Types and application of hot and cold water systems
  • Water system design and commissioning
  • Operation and inspection of hot and cold water systems
  • Water treatment and control programs
  • Microbiological monitoring
  • Cleaning and disinfection
  • Common areas and residences: Homeowners
  • Special considerations for health and care homes
  • Appendices: Risk assessment, written control plan, actions in outbreak situations, sample points
  • Glossary, references, and additional information sources

Introduction

This guide provides practical guidance to duty holders on assessing and controlling risks from legionella bacteria. Any water system with suitable environmental conditions for legionella growth is a potential risk source. Your water system has a reasonably foreseeable legionella risk if the following conditions exist:

  • Water is stored or recirculated in your water system,
  • Water temperature can be between 20–45 °C in all or part of the system,
  • There are deposits such as rust, sludge, scale, and organic matter that support bacterial growth,
  • Water droplets can form and spread,
  • There is a possibility that employees, contractors, visitors, or others may be exposed to contaminated water droplets.

Health and Safety at Work Act

Risks arising from legionella bacteria fall under the Health and Safety at Work Act 1974. The Management of Health and Safety at Work Regulations 1999 provide a general framework, while the Control of Substances Hazardous to Health Regulations (COSHH) 2002 impose specific duties for assessing, preventing, or controlling risks from hazardous substances including biological agents.

The key elements of COSHH are:

  • Risk assessment,
  • Prevention of exposure or substitution with a less hazardous substance or method where possible,
  • If prevention or substitution is not possible, control of exposure,
  • Maintenance, examination, and testing of control measures,
  • Provision of information, instruction, and training to employees,
  • Health surveillance of employees where necessary.

Other Relevant Legislation

  • Notification of Cooling Towers and Evaporative Condensers Regulations 1992: Employers operating cooling towers or evaporative condensers must notify the local authority in writing.
  • Reporting of Injuries, Diseases and Dangerous Occurrences Regulations (RIDDOR) 2013: Employers must report work-related accidents and diseases to the HSE. Cases of legionellosis are reportable when relevant conditions are met.
  • Health and Safety Representatives and Committees Regulations 1977 and Safety Representatives and Safety Committees Regulations 1996: Employers must consult with employee representatives or employees on health and safety matters.

Identification and Assessment of Risk Sources

Conducting and keeping up-to-date a legionella risk assessment is a legal requirement under health and safety laws. The duty holder must appoint a competent responsible person or persons to carry out this assessment and manage the control plan. These persons should have a good understanding of the water systems, associated equipment, and all components.

The following should be considered during the risk assessment:

  • Water storage or recirculation in the water system,
  • Water temperature between 20–45 °C,
  • Presence of deposits such as rust, sludge, scale, organic matter, and biofilm that support bacterial growth,
  • Possibility of water droplet formation and spread,
  • Potential exposure of employees, contractors, visitors, or the public to contaminated droplets.

The risk assessment should include a site inspection of water systems and relevant health and safety precautions (working at height, confined spaces, work permits, etc.).

Schematic Diagram: A simplified and accurate representation of the water system that helps quickly and easily understand the system structure. It is not a technical drawing but shows equipment, valves, filters, and unused parts in the system.

If the risk assessment concludes there is no reasonable risk or risks are properly managed with controls, the assessment is complete. However, existing controls must be maintained. Risk assessment is an ongoing process and should be reviewed especially in the following cases:

  • Changes in the water system or its use,
  • Changes in building use,
  • New risk or control information,
  • Reduction in effectiveness of control measures,
  • Significant personnel changes,
  • Occurrence of a legionnaires' disease case.

Communication is critical during the risk assessment process. Risks should be shared with management and prioritized.

Risk Management

Poor management, lack of training, and poor communication are contributing factors in legionnaires' disease outbreaks. Persons responsible for risk assessment and implementation of controls must be competent, trained, and aware of their responsibilities.

The duty holder must appoint a competent responsible person to control risks. This person should have authority, knowledge, and experience, receive regular training, and understand their role well. If the duty holder is competent, they may appoint themselves. If there are multiple responsible persons, duties and responsibilities must be clearly defined.

The duty holder may obtain external expert support but retains ultimate responsibility. The adequacy and compliance of external services must be ensured.

Prevention or Control of Risk

First, it should be assessed whether legionella risk can be prevented. If not, effective control measures must be applied to manage the risk. The written control plan should be specific to the risk assessment and appropriate for the systems.

Measures should include:

  • Proper control of water spray formation,
  • Prevention of conditions that support growth of legionella and other microorganisms,
  • Prevention of water stagnation in the system; regular water movement, shortening pipe lengths, removal of unused pipes and dead legs,
  • Use of materials that do not harbor bacteria or support microbial growth (compliance with the UK Water Fittings and Materials Directory, BS 6920 standard),
  • Keeping the system and water clean,
  • Water treatment to control or limit microbial growth,
  • Monitoring of applied control measures,
  • Keeping records of maintenance, repair, and other activities.

Record Keeping

Duty holders must keep regular and complete records of risk assessments, control plans, applied measures, monitoring results, and maintenance activities.