With many offices and workplaces preparing for staff returning to work over the coming, managers will be anxious to manage the risks associated with this.  A hazard that may be overlooked by workplaces is that of Legionella.  Legionella can cause Legionnaires disease, a potentially fatal form of pneumonia. The elderly, young, people with immunosuppressed systems and persons with underlying respiratory conditions are most at risk.  Outbreaks over the years have resulted in numerous deaths.


Legionella & Covid-19

Legionella bacteria thrives in water that is left stagnant between temperatures of 20 – 45 oC and the areas that are most at risk legionella proliferation are:

  • Hot and Cold water systems
  • HVAC systems
  • Spa pools
  • Cooling Towers
  • Humidifiers
  • Spray wash units
  • Fire suppression systems

The current Covid-19 pandemic and the addition of the recent warm weather have resulted in conditions that offer legionella a significant opportunity to grow and proliferate within water systems. Businesses that have reduced staff numbers or have temporarily closed will have had water systems used less frequently, therefore creating stagnant areas and dead legs.

With the correct conditions, for example, warm water, the presence of microorganisms and nutrients in the water or materials such as rust, the bacteria can grow and multiply to high levels, which increase the risk of exposure. The bacteria tend to grow in biofilms (slime). Biofilms are likely to form on surfaces where there is low water flow or water is allowed to stagnate. Low or no water flow and stagnation can occur during temporary water system closures.

Control of legionella within a water system is primarily tackled by temperature control together with a flushing regime of water outlets.

Companies need to have a legionella control plan which will identify key risk areas, identify personnel whose responsibilities are to monitor water systems.

Companies who are reopening in the coming weeks will have to:

  • Identify key workers who carry out safety-critical activities and plan for what should happen if they become ill or have to self-isolate. This may involve providing additional instruction, information and training to other employees and familiarizing them with the Legionella control plan and the required controls and checks to be carried out.  
  • Ensure that the controls identified in the Legionella control plan are adhered to, so far as reasonably practicable, for example, flushing of outlets, continued chemical dosing of evaporative cooling systems and so on. Controls may need to be adapted due to changing circumstances. Changes to control should be proportionate to risk and based on a review of the risk assessment.
  • For premises with simple water systems, which have had to shut down, such as small shops and hairdressers, if access is still permitted, then extended weekly flushing of all outlets will assist in maintaining microbiological control.
  • In the event it is no longer feasible to continue ongoing control, water systems should be safely shutdown. In general, water systems should be left filled with water and not drained down. With large water systems, residual water or moisture will remain within the system if drained and biofilm can develop where there are pockets of water or high humidity. The water in the system helps to avoid other problems associated with systems drying out, including failure of tank joints and corrosion in metal pipework.
  • Where wet cooling systems are being shut down, competent advice should be obtained prior to shut down. Proper decommissioning (draining, sealing and addition of desiccant) may be required in order to minimise the Legionella risk when put back into service.


Legionella Risk Assessment

Environmental Efficiency Consultants provide a full Legionella Risk Assessment and control plan together with legionella testing of the water systems to provide picture of the bacterial health of the systems.  This service offers a structured support to businesses with clear and easy to follow steps on how to control the risk associated with Legionella.