Air conditioning and ventilation during the COVID-19 pandemic

In light of the COVID-19 pandemic, and with workplaces and offices slowly returning to site following the easing of lockdown restrictions, the Health and Safety Executive has issued guidance around the safe operation and maintenance of air conditioning systems in the workplace.

The risk of COVID-19 spreading through air conditioning systems has been deemed to be very low and the continued use of most types of air conditioning systems is not discouraged however it is recommended that the use of centralised ventilations systems which remove and re-circulate air to different rooms is adapted to avoid recirculation of air between spaces, rooms or zones occupied by different people. Instead, it is recommended that the recirculation function is disabled, and a source of fresh air is utilised instead. Air conditioning systems which mix some extracted air with a fresh air supply and redirect it to the room do not need adjusted as this will still increase the fresh air ventilation rate and increase air disturbance. “Dilution” of internal air with fresh air supply should reduce any risk of potential airborne viral transmission by reducing exposure time to any airborne viral particles, and also reduce risk of these particles settling on surfaces. Evidence shows that the virus can survive on surfaces for up to 72 hours and as such, any action that can be taken to reduce this risk is recommended.

Additionally, CIBSE have published guidance which states that buildings with mechanical ventilation systems should increase the operational times of the systems. Even if buildings are unoccupied, it is not recommended that ventilation systems are shut off, rather they should continue to operate continuously at reduced speeds.

Portable units or units in individual rooms do not need adjusted as these operate on total recirculation.

Employers have a legal duty to ensure an adequate supply of fresh air in the workplace and this obligation remains unchanged in light of COVID-19. In fact, the importance of this obligation has been enhanced by the spread of the pandemic as good ventilation can help reduce the risk of the COVID-19 infection by enhancing air disturbance. To facilitate this, windows and doors should remain open where safe to do so to ensure a steady supply of fresh air (fire doors and safety windows should remain closed). Employers should consider if there are any ways to prevent accumulations of “stagnant” air, for example by using ceiling fans as the risk of transmission through such fans is considered very low. Partial recirculation of air within designated areas through, for example, a local fan coil unit may also be recommended in order to help maximise the air exchange rate with outside air and to minimize the risk of any pockets of stagnant air.

It is recommended that, if employers have any concerns surrounding the safe operation of heating, ventilation and air conditioning systems (HVAC) that they contact their HVAC engineer.