As of Monday (13^th December), Government has once again advised that people work from home where possible as the UK braces for the more transmissible Omicron variant of Covid 19. Hopefully less footfall in our busy city centres and work spaces will be enough to quell yet another wave of coronavirus and save Christmas plans for everyone who was hoping for a more ‘normal’ festive period.

What this means for places of work, particularly large commercial offices, is that yet again they are faced with low occupancy and with it, an enhanced risk of Legionnaire’s disease. For most of these establishments, the Christmas break meant closure for a week or so anyway, but now this empty period has been abruptly extended and who knows what will happen in the New Year.

Why do empty buildings mean increased legionella risk?

Water systems, including potable water and water used for heating and cooling, are designed to be used, specified for a particular application based on occupancy. Legionnaire’s disease is spread by the inhalation of water droplets containing Legionella bacteria, so particular care must focus on hot and cold-water outlets, wet air conditioning plant and cooling towers.

Without people using these water systems, flushing water through pipes and taps, stagnation occurs, creating the ideal environment for Legionella and other bacteria to thrive.

What should you do if you’re building is going to be empty?

According to the Health & Safety Executive (HSE), operations should be reviewed, and plans made in advance of a period of shutdown. In the case of the lockdowns we have experienced over the past two years, including this most recent advisory one, this has not always been possible, however.

If you do know that your water systems are going to be unused for a significant period of time (7 days or more), then you need to make sure you have a flushing programme in place or a suitable maintenance programme in place to ensure that systems stay clean and ready to use when the workplaces open back up again. It is advisable to speak with your water consultant or legionella contractor to discuss your concerns.

A supplementary risk assessment in accordance with ACoP L8 should be carried out, based on the specifics of your building. This should include the temporary measures that are required to maintain a healthy water system, based on the reduced capacity and be focused on potential areas of risk such as aerosol generation that could expose stagnant water particles to the building users on their return to the office.

Stopping the operation of large water-based plant, such as cooling towers and evaporative condensers, can lead to particular risk, as these systems contain large volumes of water and during operation can expose a large number of people to aerosols. You should consult with your water treatment supplier regarding safe shut down and start up procedures.

Steps to prevent legionella in unoccupied buildings:

• Stop stagnant water: Think about locations where water collects and is unmoving, such as tanks and tap outlets which will only be used during normal building use.
• Increase testing regimes: If the period of in-occupancy is significant, consider ramping up water testing activities.
• Flush underused water outlets regularly.
• Turn off water heaters and store water at less than 20˚C. Legionella bacteria thrive in warm water between 20˚C and 45˚C.
• Consider water sampling if control procedures as mentioned above have not been fulfilled
• Disinfect water systems prior to reoccupation if considered necessary.

When offices are reopened, a legionella risk assessment must be completed again to ensure that the new building occupation levels have not affected the risk. If we are put in a position where full occupancy is not an option, then consideration should be given to the water systems that will remain unused in relation to further control measures that may be required.

Need help keeping your buildings legionella free?

GMS provides a range of Legionella Risk Assessment and Water Treatment services, contact us to see how we can help.