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The Part that Good Ventilation Plays in Controlling the Risk of COVID-19

Whilst masks and social distancing measures are highly visible signs of Covid controls, the role of ventilation, which is largely unseen, plays a hugely important part in controlling the risk of infection which will be especially important as we begin to open up our event spaces and offices as the lockdown is lifted. 

The acts of breathing, talking, coughing and sneezing all produce droplets and aerosols that may, if the host is infected, contain pathogens.  Larger droplets fall by gravity within 2m from the source, hence the need for social distancing.  The droplets land on surfaces and can therefore get onto hands – hence the importance of regular hand washing and avoiding touching the face.  Smaller aerosols, however, can stay airborne for hours, which enables them to travel longer distances where they could infect secondary hosts, particularly in poorly ventilated spaces.  It should also be remembered that high levels of chemicals in enhanced cleaning regimes can themselves create a hazard if the areas in which they are used are poorly ventilated.

The law says employers must make sure there is an adequate supply of fresh air (ventilation) in enclosed areas of the workplace1. This has not changed during the pandemic.  It applies equally to offices and public spaces in event venuesHSE Guidance2 states that employers should be maximising the fresh air in a space and this can be done by:

  • natural ventilation which relies on passive air flow through windows, doors and air vents that can be fully or partially opened3 
  • mechanical ventilation using fans and ducts to bring in fresh air from outside4 
  • a combination of natural and mechanical ventilation, for example where mechanical ventilation relies on natural ventilation to maximise fresh air. 

It is important to distinguish air ventilation which brings in fresh air from air circulation which merely circulates the air and whilst it can have a cooling effect, it actually increases the problems because it spreads the infectious aerosols further.   

The government and SAGE have published detailed guidance on the use of ventilation in controlling risk5&6.  Broadly government advice is that ventilation should be considered as part of a package of measures in the event or office risk assessment process with the following considerations: 

  • nature and type of ventilation (mechanical, natural or both) 
  • identify areas that are not ventilated or are poorly ventilated 
  • consider the number of people who occupy the area and for how long 
  • the size of the area and whether it allows for social distancing
  • the activities take place in the area that would increase the production of aerosol transmission such as physical exertion, shouting or singing 
  • workplace features that could prevent air circulating (e.g., confined space such as lift shafts or meeting rooms that are not ventilated) 
  • the presence of desk or ceiling fans which circulate the air and therefore contribute to the problem. 

Event spaces have a natural advantage of high roof spaces and during the construction phases the fact that open cargo doors will often provide very effective natural ventilation.  Both in venues and offices, however, it is vital to recognise that increasing air flow by opening doors must not be at the expense of fire separation measures and fire separation doors must remain shut or on release mechanisms linked to the fire alarm system.  Fire risk is still by far the greater risk. 

The safe and effective operation of ventilation systems will be on a long list of building system inspection criteria that event venues have to consider as they open up again especially if it has not been possible to maintain them with the same regularity or thoroughness during the pandemic.  Even dormant systems can be compromised for example with erosion due to water ingress or water content in the air, the accumulation dust and detritus or activities of vermin such as rats and mice.  Event companies and venue owners are strongly advised to ensure that ventilation systems, as well as being effective, are maintained and therefore safe and fit for purpose.  Venues may have workshops with local exhaust ventilation for specific functions like dust extraction.  These must be considered in the overall ventilation plan for operation and maintenance.  This does not apply to portable systems used in event construction although clearly the contractor has a responsibility to ensure that they are also maintained and operated safely. 

There is wide recognition that ultimately Covid-19 cannot be entirely defeated and that once the population has achieved herd immunity through vaccination it will probably remain endemic just like colds and flu.  It remains to be seen the extent to which this acceptance will lead to the stripping away of infection controls like social distancing and the wearing of masks as we restore our normal working lives.  Good ventilation, however, which is shown to reduce the risk, does not require intrusive controls such as one-way systems or established behaviour norms like social distancing and is known to improve the healthy working environment.  Event companies should review their provision in both event spaces and offices not just for the immediate return to work but to ensure provision of healthy working environments and public spaces going forwards. 


  1. Workplace (Health, Safety and Welfare) Regulations 
  2. www.hse.gov.uk/coronavirus/equipment-and-machinery/air-conditioning-and-ventilation/
  3. HSE Guidance - natural ventilation 
  4. HSE Guidance  - mechanical ventilation 
  5. Government guidance ventilation of indoor spaces to stop the spread of corona virus (Covid-19), March 4th www.gov.uk/government/publications/covid-19-ventilation-of-indoor-spaces-to-stop-the-spread-of-coronavirus  
  6. Government environmental modelling group  - Role of ventilation in controlling SARS-CoV-2 transmission, 30 September 2020 www.gov.uk/government/publications/emg-role-of-ventilation-in-controlling-sars-cov-2-transmission-30-september-2020  


Disclaimer: The information and opinions expressed on this webpage are those of the author and not necessarily those of the Institution of Occupational Safety and Health (IOSH).