Workplaces & COVID-19

Orla Hegarty , 10 September 2021

Orla Hegarty, Assistant Professor at University College Dublin, has been advocating and educating on the important issue of ventilation in buildings for the last 18 months. Here she shares some clear, simple advice and watchpoints.

COVID-19 is a respiratory virus, it is caught from breathing. In the open air, the virus is diluted and dispersed in the air, but inside buildings, aerosols – the particles small enough to remain in the air – can linger, spread and build up to dangerous levels, similar to cigarette smoke. Ventilation is key to prevention. In one study, risk was shown to be 20 times higher indoors.

Air quality in buildings can be measured, managed and monitored, so improving ventilation reduces or eliminates these risks.

Active and targeted prevention of specific high-risk conditions, such as in meat plants, overcrowded housing and schools, is key to both keeping buildings open and people out of hospital, without compromising the health services or the economy.

Also see the Ventilation Resource Round-up.

Advice & watchpoints

COVID-19 is predominately inhaled in infected air. It is rarely caught from surfaces and normal cleaning is adequate.

Precautions for aerosol transmission are masks and clean air. Masks and clean air can reduce virus risk up to 90%… so these are TOP priority.

Ventilation & clean air
  • Clean Air can be achieved with ventilation (diluting with fresh air) or filtration (cleaning air) or both. A CO2 monitor shows if ventilation is inadequate (<800 is recommended). At 800ppm, about 1% of every breath is air breathed out by someone else… at over 800ppm, the risk rises.
  • Natural ventilation (windows/doors/wall vents) – keeps air moving with cross-ventilation. Calm days and cold days are higher risk.
  • Mechanical ventilation – get an engineering check on operation of system/settings/filters. Consider plug-in HEPA filtration (many brands available).
  • HEPA is recommended and it’s cheap. Avoid ‘air purifiers’ using: ionisers, ozone systems or plasma systems. These systems may be ineffective and may be unsafe. UVG (ultraviolet germicidal irradiation) has some specialist applications, so get independent specialist advice.
Masks – everywhere at all times
  • In buildings and shared vehicles, rooms, offices, lifts, toilets, corridors and stores. Delta is highly transmissible. People have been infected in poorly ventilated unoccupied rooms.
  • Consider arrangements for eating/drinking (outside, in separate rooms, in cars) to reduce risk of break-room outbreaks. If no space/no time, consider no talking, while masks are off for eating (yes, it makes a difference to virus spread).
  • Two-metre distance is NOT a protection in shared indoor air. Perspex screens are NOT a protection. Cubicle partitions are NOT a protection. Poorly fitting masks are NOT a protection. Vaccines are sun-block, not a bullet proof vest.
  • A good mask makes a big difference – comfort (so you keep it on), filtration (so fabric blocks aerosols) and fit (so no gaps). An N95/FFP/KN95 mask is better than a surgical mask. A cloth mask over a surgical mask is also effective.

Clean air protects from every new variant, respiratory virus (including flu) and pollution, pollen and odours. People who work in clean air perform better and are ill less. Better ventilation is part of building energy upgrades for climate change… so bring it forward?

Final word

Finally, distancing is NOT a protection when people share indoor air. Infected air can spread to fill a room, it can be trapped and linger for hours after someone has left. The following two-minute video by Holt Architects shows how the virus can spread indoors. Stay safe.


Orla Hegarty is an architect and assistant professor at the School of Architecture, Planning & Environmental Policy in University College Dublin. Her area of research is the built environment, housing and the construction industry, with particular interests in building safety, sustainability and quality. In the last year she has been actively collaborating in cross-disciplinary research into Covid-19, and understanding how the environmental science of pandemic is key to suppression and using buildings at low risk. She is a member of a new expert group advising NPHET.