Derry City & Strabane - Environmental Health
Health & Community Wellbeing




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CIEH - Legionnaires COVID-19 Guidance

This guide will help duty holders and enforcement officers to understand and minimise the risks of Legionnaires’ disease following COVID-19.  Legionnaires’ disease is a type of pneumonia which can cause serious illness in susceptible individuals. It is caused by the growth of Legionella in building water systems which are not adequately managed. When tiny droplets of water (aerosolised water) containing the Legionella bacteria are breathed into a susceptible persons lungs, Legionnaires disease can result. 

When buildings re-open after lockdown, it is essential that water systems are not simply put back into use. This is because there is potential for increased levels of Legionella and other waterborne pathogens to be present in the system due to low water usage. 

During the COVID-19 pandemic there is also potential for an increased number of people to have susceptibility to Legionnaires’ disease due to a compromised respiratory system during or after infection with the Coronavirus. Extra care is required. 


The law

It is a legal requirement under the Health and Safety at Work etc. Order 1978 for employers, business owners and landlords to manage the risks of exposure to Legionella.  It is very important that dutyholders manage and keep all water systems safe whilst closed or during partial shutdowns for the health and safety of guests, visitors and staff on re-opening. 


Who is this guidance document aimed at?

This guidance is aimed at duty holders i.e. individuals responsible and/or accountable for managing and maintaining buildings.  The type of buildings covered include retail outlets, offices, hairdressers, beauty salons, hotels, pubs, clubs, restaurants, sports centres/clubs, gyms, residential buildings as well as campsites and cruise ships.


How do I re-open my business safely?

The first step prior to re-opening is reviewing your risk assessment. By law, it is necessary to review your Legionella Risk Assessment when there is a significant change. The ACOP L8 states a significant change is;

  • When there is reason to be assume it is no longer valid
  • Changes to the water system or its use
  • Changes to the use of the building in which the water system is installed

Building shut down and or low usage during COVID-19 is a significant change. 


How do I review my Legionella Risk Assessment    

Your “competent person” must review your risk assessment.  

Under the Approved Code of Practice The control of Legionella bacteria in water systems (ACOP L8) a “competent person” is required to manage your water system and ensure the system is safe when you re-open your business.  This should be someone with sufficient authority, competence, knowledge of the system, and experience. Where necessary, identify a competent water treatment consultant to assist.  It is recommended that you assess a potential contractor to ensure their competence for your water system. The Legionella Control Association can assist in finding competent contractors.  


How can I re-open safely immediately after shut down?

There are numerous different water systems with differing operational levels. To re-open safely, your “competent person” must first review the current risks, appraise the site's water system and determine the control measures. 

However, consider the following scenarios to determine the necessary measures to safely re-opening. 

  1. Have you maintained your normal control regimes? 

If you have been safely flushing the water system and the water heater has been kept running during the building shutdown or during low usage and you have records to demonstrate this, you can usually re-open safely. As an added precaution, you could organise your water treatment consultant to carry out a full disinfection (mains injection clean and pull through to all outlets) to achieve 50 ppm free chlorine or equivalent biocide for at least an hour. This can be followed by legionella sampling 48 hours post disinfection treatment. This would be especially important if there are problems with temperatures during weekly flushing or problems with biocide levels. 

Example of a normal control regime;

  1. Hot water is circulating throughout all parts of the system and any stored water is maintained at ≥60 °C and flow temperature is maintained at ≥50 °C and the return on all loops is at ≥50 °C. If using a biocide, maintain target levels throughout all of the system.
  2. Weekly flushing of all hot and cold outlets (showers and taps) to ensure temperature of hot reaches ≥ 50 °C within one minute and temperature of cold reaches ≤20 °after running the outlet (normal flow, avoid splashing) for 2 minutes.
  3. Where thermostatic mixer valves (TMV) are installed, the hot water and cold water supply to the TMV are tested weekly.
  4. All WC cisterns, urinals, by-passes and any other points on the network are being flushed daily.
  5. Drinking water storage tanks remain at 0.2 - 0.5ppm of free chlorine

Note: When flushing, it is important to minimise aerosol production. For example, if a person is tasked with flushing shower heads, it is good practice to flush into a part filled container of water in order to reduce aerosol generation. You should ensure the showerhead is submerged under the level of the water in the container. 


2.  Did you stop or partially shut down your normal control regimes? 

If you closed your building or part of your building for more than a month and or, no-one has been using the building and or you made a decision to not to heat your hot water to conserve energy, there is increased risk of legionella growth. It is therefore necessary BEFORE your return to your normal control regime to carry out a full system disinfection of the cold-water system, flushing through to all outlets to achieve 50 ppm free chlorine or equivalent biocide for at least an hour. This can be followed by legionella sampling 48 hours post disinfection treatment. 


3.  Did you drain your system when closing your building?

If you drained your system before closing your building, there is a potential risk when restarting that there will be water and condensation present. This will allow microorganisms including Legionella to grow. It is also therefore necessary to carry out a full system disinfection (mains injection clean and pull through to all outlets) to achieve 50 ppm free chlorine or equivalent biocide for at least an hour. This can be followed by legionella sampling 48 hours post disinfection treatment. 

Only when you are satisfied that the hot and cold and water systems are under control you can re-open the building. You should ensure you keep all documentation for inspection including the review and update of your risk assessment and cleaning and monitoring records. Always ensure good record keeping practices by evidencing who carried out monitoring and include times, dates and signatures. Remember, when accessing the various parts of the water system ensure other health and safety risks are minimised to prevent harm for example, working at height and manual handling.  


Reference Advice 

HSE Legionella and Legionnaires' Disease Advice

HSG274 Part 2 - The Control of Legionella Bacteria in Hot and Cold Water Systems

HSE Legionella & Legionnaires' Disease FAQs

The Legionella Control Association

HSE Advice on Legionella Risks in Your Workplace

Advice on the investigation of notifications of Legionnaires’ Disease : Environmental Health and Public Health England. 

The Law

The Health and Safety at Work Order (Northern Ireland) 1978

Management of Health and Safety at Work Regulations (Northern Ireland) 2000

Control of Substances Hazardous to Health Regulations (Northern Ireland) 2003

L8 Approved Code of Practice and guidance on regulations



CIEH is grateful to the following for assistance in providing this guidance:

Angeline Wolfe, Chartered Environmental Health Practitioner, Co-founder My Compliance People Contact for advice:

Pete Tyson, Primary Water Solutions, Contact for advice; 01454 501 818