Legionella risk following lockdown

Legionella risk following lockdown

  • Date: Friday 29th May 2020
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With buildings looking to reopen after a prolonged period of closure, and during a warm weather period, there may be another hazard waiting around the corner.  

Legionella is a harmful bacterium which is within most water supplies. In certain percentages it is hazardous to occupants. Most premises will have completed a legionella risk assessment and put into place controls called ‘the scheme of control’. 

Many business premises will have not been used during this lock down period, and the current warm weather provides the ideal conditions for legionella growth. These include water temperatures between 20°C – 45°C, stagnant water and deposits that can support bacterial growth, such as rust, sludge, scale, organic matter and protozoa-rich biofilm.

To control the risk from legionella, building occupants have two choices:

  1. Maintenance of the scheme of control (as derived from the legionella risk assessment) during the lockdown period - maintaining appropriate records; 


  1. When reoccupying the building the water system should be reinstated via a mixture of the following methods:
  • Flushing through the entire system (this process may not be adequate by itself);
  • Carry out a water system disinfection, using biocides or reheat the hot water vessel to >60°C and flush through all outlets – avoid scalding risk;
  • Monitor temperature levels for at least 48 hours, then take legionella water samples from sentinel points in the system. Water samples should be sent to a UKAS accredited laboratory for analysis;
  • Reintroduce the ‘scheme of control’ once the water system is back under control
  1. If in doubt, consider a legionella re-assessment of the premises by a competent person.   

  To ignore the risk from legionella may place the occupants of the premises at risk.  

Source: Ian Tagg

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