The importance of Ventilation in the fight against COVID-19

Good ventilation is a very important way of diluting any airborne pathogens (viruses and bacteria) and there is good evidence that demonstrates room occupants are more at risk of catching an illness in a poorly ventilated room than in a well-ventilated room.

This is because, in a poorly ventilated room, occupants are exposed to a higher concentration of airborne pathogens, and the risk will increase the longer people stay within the room.

The ventilation rate (the flow of air into a room) and effectiveness play a role in both airborne exposure and deposition rates.

Evidence is that Covid-19, can spread by aerosols – which are released by an infected person when they cough, sneeze, talk and breathe, as well as the larger droplets that are released. Larger droplets, as we know, will fall by gravity and influences the 2m social distancing measures (in Wales) to reduce spread. However, these fine aerosols can remain airborne for several hours.

To minimise the risks of airborne transmission, the current advice is to increase the air supply into a room and exhaust ventilation (ways that air can leave a room) and to ensure as much outside air is brought into the room, as is reasonably possible. By doing this the idea is that any airborne pathogens e.g. COVID-19 are diluted as much as possible and then using an extract system that they are carried outside. This reduces the chances that they can become deposited on surfaces or inhaled by room users. This can be done via mechanical (some form of built in air system) or natural ventilation - doors and windows.

Using mechanical ventilation

If you have mechanical ventilation systems you will need to find out whether they supply air from outside or recirculate air. Some air conditioning systems form part of the mechanical ventilation system whereby the outside air is first ‘conditioned’ before being moved along ductwork to the room. This conditioning can include warming or cooling of the air, as well as adjusting the humidity of the air. Some systems that are commonly known as 'air conditioning', only condition the air in a room. These systems take air already in a room and warm or cool it before releasing it back (recirculate it) into the room. It is important to understand that these systems are not delivering outside air and are therefore not diluting any airborne pathogens.

Ventilation systems should be run at a higher volume flow rate – approx. 2 air changes per hour, as a guide. Ventilation systems should be turned on a minimum of 2 hours before building usage and should remain on, at a lower flow rate post use for around 2 hours.

Recirculation/transfer of air from one room to another should be avoided unless this is the only way of providing adequately high ventilation to all occupied rooms. Recirculation of air within a single room where this is complemented by an outdoor air supply is acceptable.

Not all buildings will have a form of mechanical ventilation and you will rely on natural ventilation (windows and doors).

Natural ventilation

For small buildings with limited ventilation, openings external doors may be used to increase ventilation as long as care is taken over security. Propping open internal doors may be appropriate where it delivers a significant increase in air movement and ventilation rate. It is important to note that fire doors should not be propped open unless fitted with approved automatic closers so that they function as fire doors in the event of an alarm or fire.

If possible, windows should be open at least 15 minutes prior to room occupation. As the weather is beginning to warm opening windows is a typical behavioural response, however it is important to ensure that windows are open even if it is cooler outside. If it is windy, cold or raining then it may not be practical to fully open the windows/vents, however they should be open as far as reasonably possible without causing too much discomfort.

In rooms and zones where there is no direct supply of outside air then consideration should be given to prohibiting access to these spaces by people, especially where it is likely that they would be occupying such a space for considerable lengths of time (longer than 30 minutes). This may include basement rooms or storage areas which rely on infiltration of air from other spaces.

Some spaces may not have an identifiable ventilation system. For example, it is common for there to be no ventilation in corridors or staircases as these are deemed to be transient spaces and they rely on air infiltration from neighbouring spaces. However, rooms/zones that are occupied routinely without any obvious ventilation strategy are going to be a significant risk and the ventilation provision should be addressed.

Action – check the ventilation systems in your work place, refer to the CIBSE guidance and speak to your ventilation engineer for further advice.

Alium Health, Safety & Wellbeing can support you in keeping your workplace safe and healthy. If you need any advice or would like to discuss our services in more detail please contact us.


Tel: 07974 341852/ 07816 765111

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