Legionnaires' Disease: Technical Guide Part 1 - Control of Legionella Bacteria in Evaporative Cooling Systems

This guide is prepared for duty holders such as employers, persons in control of premises, and others responsible for health and safety. It provides practical advice to help them fulfill their legal obligations, including identifying and assessing risk sources, preparing a plan to prevent or control risk, implementing, managing and monitoring measures, keeping records of measures, and appointing a manager to take responsibility for others.

Contents

  • Introduction
  • Evaporative cooling systems: Types, design and operation
  • Cooling water treatment programme requirements
  • Inspection, cleaning and disinfection procedures
  • Monitoring water quality and understanding water treatment analysis reports
  • Appendix 1: Legionella risk assessment
  • Appendix 2: Legionella written control plan
  • Appendix 3: Actions in the event of a legionellosis outbreak
  • Glossary
  • References
  • Additional advice
  • Acknowledgements
  • Further information

Introduction

This guide provides practical guidance to duty holders on assessing and controlling risks from legionella bacteria. Any water system can be a potential source of legionella bacteria if suitable environmental conditions exist. Legionella risk is reasonably foreseeable if:

  • Water is stored or recirculated in your water system,
  • Water temperature in one or more parts of the system can be between 20–45 °C,
  • There are deposits such as rust, sludge, scale and organic matter that support bacterial growth,
  • Water droplets can be formed and dispersed,
  • Employees, contractors, visitors etc. can be exposed to these contaminated water droplets,

there is a risk of legionella.

Health and safety legislation

Risks from legionella bacteria are covered by the Health and Safety at Work etc. Act 1974 (HSW Act). The Management of Health and Safety at Work Regulations 1999 and the Control of Substances Hazardous to Health Regulations 2002 (COSHH) provide a framework for assessing, preventing or controlling these risks. The key elements of COSHH are:

  • Risk assessment,
  • Prevention of exposure or substitution with a less hazardous substance or process where possible,
  • Control of exposure where prevention or substitution is not possible,
  • Maintenance, examination and testing of control measures,
  • Provision of information, instruction and training for employees,
  • Health surveillance of employees where there is a risk of identifiable disease or adverse health effect from exposure.

Duty holders must take appropriate measures to ensure the health and safety of their employees and others who may be affected. They must appoint a competent person who can identify, assess, manage, control, keep records of risks and fulfill other legal duties.

Other relevant legislation

Employers must also comply with the following legislation:

  • The Notification of Cooling Towers and Evaporative Condensers Regulations 1992,
  • The Reporting of Injuries, Diseases and Dangerous Occurrences Regulations (RIDDOR) 2013,
  • The Safety Representatives and Safety Committees Regulations 1977,
  • The Health and Safety (Consultation with Employees) Regulations 1996.

The Notification of Cooling Towers and Evaporative Condensers Regulations require employers to notify the local authority in writing. RIDDOR requires reporting of legionellosis cases associated with water-using cooling systems at workplaces. Employers must also consult safety 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 to carry out this assessment and manage the control plan. This person should understand water systems, equipment such as pumps and heat exchangers, and all system components. The following should be considered during the risk assessment:

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

The risk assessment should include a site survey of all water systems and relevant health and safety measures. Appendix 1 summarizes risk assessment requirements for evaporative cooling systems. BS 8580:2010 and The Water Management Society’s risk assessment guide are also useful resources.

The risk assessment should include the following elements:

  • Clear definition of management responsibilities,
  • Competence and training status,
  • Description of the water system and up-to-date schematic diagram,
  • Risk assessment,
  • Safe operating procedures and control measures,
  • Monitoring, inspection and maintenance procedures,
  • Monitoring and inspection results,
  • Limitations of the risk assessment,
  • Plan for regular review of the risk assessment.

Schematic Diagram: A simplified but accurate representation of the water system. It is used to 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 by controls, the assessment is complete. However, existing controls must be maintained. Risk assessment is an ongoing process and should be reviewed especially when there are system changes, new information, ineffective controls, personnel changes or a legionnaires' disease case.

Risk management

Poor management, lack of training and poor communication can contribute to legionnaires' disease outbreaks. It is important that persons responsible for risk assessment and implementation of controls are competent, trained and aware of their responsibilities.

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

The duty holder may obtain external expert support but retains ultimate responsibility. External service providers must be competent and perform their duties to required standards. Codes of conduct recommended by organizations such as the Legionella Control Association can be helpful.

Prevention or control of risk

First, it should be assessed whether legionella risk can be prevented. For example, using a dry system instead of a wet cooling tower may be possible. If a wet system is necessary, effective control measures must be applied to manage risks. The written control plan should be appropriate to the risk assessment and specific to the systems.

Measures should include:

  • Proper control of water spray emissions,
  • Prevention of conditions that support microbial growth including legionella,
  • Prevention of water stagnation in the system; regular water movement, keeping pipe lengths short, removal of unused pipes and dead legs,
  • Use of materials that do not harbor bacteria or provide nutrients for microbial growth (compliance with Water Fittings and Materials Directory, BS 6920 standards),
  • Keeping the system and water clean,
  • Treatment of water to control or limit microbial growth,
  • Monitoring of applied control measures,
  • Keeping records of maintenance and other operations.