Better ventilation - the forgotten transmission route of COVID-19

Ventilation advice - how to go back to work safely

Lib Dem Councillor John Milne says, "Horsham Liberal Democrats are calling on West Sussex County and Horsham District Councils to ensure that all non-domestic buildings in the area, including schools, shops and offices, are properly assessed to ensure ventilation systems are working effectively to circulate outdoor air, so that the risk of infection is reduced as much as possible."

The government’s latest policy for dealing with the COVID-19 emergency is now shifting away from total social distancing to a policy of partial back-to-work[1]. This means we face a new challenge, which is how to minimise the risk of picking up infection in shared spaces in offices and shops.

According to Professor Alan Penn, one of the government’s senior scientific advisers, the virus can be transmitted in three main ways:

  • From droplets (which is where the two-metre rule comes from)
  • By touch (which is prevented by hand washing and protective clothing)
  • From fine particles (aerosols) created by coughing, sneezing, talking and breathing[2]

It’s the third route that must not be forgotten as we go back to work and potentially spend hours in the company of other people. Viruses shed in fine droplets that can remain airborne for several hours, but quickly disperse outdoors. However, in an enclosed space with poor ventilation, they could continue to build up increasing the risk of cross-infection. The best way to minimise this risk is to maximise ventilation as recommended in the Government Covid-19 recovery strategy[1].

Although anyone with visible symptoms is likely to self-isolate, we know that some people aren’t even aware they have the virus. If they share an office for hours on end, with no ventilation, the concentration of viral aerosols will continue to increase. However, with proper ventilation, the build-up in the atmosphere will be minimised.

How to stop infection

For many buildings this simply means opening as many windows as possible and, if it is safe to do so, trying to keep entrance doors open. If you have mechanical ventilation the settings should be changed to give the maximum volume of outdoor air.

Florence Nightingale is championed as the pioneer of modern nursing, but a read of her seminal work “Notes in Nursing” will leave the reader in no doubt that her principle focus is the improvement of indoor ventilation to prevent spread of diseases.

The Chartered Institution of Building Services Engineers have produced a guidance document which recommends how to get the best out of your ventilation system[3]. For more complex ventilation systems advice should be sought from a qualified engineer and the system manufacturer.


[2] A series of tweets from Prof Marr helps explain 


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