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National shutdowns increase the risk of Legionnaires’ Disease

Legionellosis is the collective name given to the pneumonia-like illness caused by the legionella bacteria, including the most serious Legionnaires’ disease. Infection is caused by breathing in small droplets of water contaminated by the bacteria, which are commonly found in most water sources.

When water systems are in normal use, the risk of infection is diminished because the bacteria cannot multiply as effectively in water that is regularly agitated.

With water systems in many UK workplaces standing idle or operating on reduced capacity, it will be important to make sure that your premises don’t become a breeding ground for trouble when they are reoccupied – because Legionnaires’ disease can have serious or even fatal, consequences.

  • If you haven’t done so already, you should conduct a risk assessment to identify potential legionella hazards and appropriate control measures in the workplace.
  • If you already have a Legionella risk assessment, it will need to be reviewed to ensure it protects people when supplies are reinstated or returned to use.
    If the water system is still used regularly, maintain the appropriate measures to prevent legionella growth.

There are different types of water systems and these will require different actions.  The exact control measures should be detailed in your risk assessment – they will also depend on factors such as whether you have sole occupancy or work in a shared building, or if the premises are subject to any form of the external building management agreement.

Infrequently used hot and cold-water systems-

should be flushed weekly to prevent water stagnation – if you cannot do this and decide to flush out infrequently used outlets (including showerheads and taps) before a return to work then do so before the building is occupied and prevent exposure to the person(s) conducting the work, as they could inhale the bacteria from airborne droplets. 

Temperature is the main form of control used in hot and cold water systems; the bacteria are dormant below 20°C and cannot survive above 60°C, but will multiply where temperatures are between 20-45°C and nutrients (such as rust or pipe sludge) are available.

Hot and cold water systems may also use biocides (a chemical substance or microorganism intended to destroy or otherwise control a harmful organism) or other chemicals (e.g. corrosion or scale inhibitors, anti-foams, algaecides, etc.) as part of a water treatment programme.

A period of restricted working may present the ideal opportunity to have a suitably competent person review your water system – all cold-water storage tanks should be cleaned periodically and water should be drained from hot water cylinders to check for debris or signs of corrosion; water systems can then be cleaned (if required) and disinfected before the building is reoccupied.

If commercial spa pools and hot tubs are not being used, you should drain, clean and disinfect them – you should also clean and disinfect them before reinstatement.

Businesses with cooling towers and evaporative condensers should have reviewed operations in advance – and should also have plans in place to ensure safe systems of work continue during any shutdown. This includes ensuring that;

  • adequately trained personnel are available to carry out essential checks and monitoring.
  • chemical supplies are maintained and dosed appropriately.

If cooling towers and evaporative condensers are likely to be out of operation for up to a month, you should isolate fans but continue to circulate biocidally-treated water around the system for at least an hour each week.

Cooling towers and evaporative condensers that will be out of use for more than a month should be drained down and the systems cleaned and disinfected. Clean and disinfect the systems again before refilling and returning to operation.

If you need help to stop operating any of your systems, speak to your water treatment company for advice and guidance.

Regardless of what type of water system your building has, if you make significant changes to your control methods or operating strategy, workers may be exposed to additional or different risks, and you will need to;

  • review the controls in your legionella and associated COSHH (Control of Substances Hazardous to Health) assessments.
  • increase the level of monitoring during the commissioning of any new controls.
    If you need to clean water systems or handle water treatment products, it is likely that respiratory protective equipment (RPE) will be needed – any RPE provided must be suitable for the task/operator (s) that will use it and provide an assigned protection factor of at least 20.

During the current pandemic, some disposable RPE (such as FFP3 respirators) may be in short supply – especially if they are of a type also used by health and care workers.  if your usual type(s) of RPE are unavailable, you can source alternatives as long as your risk assessment demonstrates they are suitable and adequate for workers and the task; additional fit-testing will need to be undertaken for operatives using any new piece of RPE that relies on providing protection by means of tight fight forming a seal with the wearer’s face.

View our Legionnaires’ Disease White Paper to find out more information.


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