…to reduce Covid-19 cases Building ventilation is always an important part of a healthy building environment as it ensures that a steady stream of outside air is brought into the building whilst stale air is exhausted. Stale air includes bioeffluents (body odours and exhaled breath), airborne pollutants (such as smells from cleaning products and furniture), amongst others. Ventilation is also a very important way of diluting any airborne pathogens 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 with a greater amount of time spent in such an environment.
Risk = exposure x time
The risk of airborne infection to the individual can therefore be reduced by:
- Reducing time spent in the location
- Reducing airborne exposure concentration of infectious material
- Reducing risk of contact spread through regular handwashing, surface cleaning and reducing deposition of infectious particles.
Ventilation rate and effectiveness play a role in both airborne exposure and deposition rates. The risk for SARS-CoV2 transmission will be from asymptomatic or pre-symptomatic individuals who occupy a building without knowledge that they are shedding viral particles. Current government advice should be consulted with regards to reducing risks posed by symptomatic individuals. 1.1 Covid risks Evidence is beginning to emerge that SARS-CoV2, the virus which causes Covid-19, can spread by very small particles – called 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 will fall by gravity and influences the 2m social distancing measures to reduce spread. However, these fine aerosols can remain airborne for several hours. Although it can be difficult to definitively prove airborne transmission, our knowledge of other similar viruses and the emerging evidence showing high rates of infection in poorly ventilated rooms suggests that we should consider this as a potential transmission route and undertake measures to reduce that risk. These small droplets may be breathed in and cause infection. As our understanding of the significance of the various transmission routes of SARS-CoV2 develops, we recommend increasing the rate of supply of outside air to occupants wherever it is practical as a pre-cautionary measure. This is particularly important in poorly ventilated areas. Increasing the ventilation rate helps dilute any airborne contamination and reduces the risk of exposure for building users. This guidance is subject to change as SARS-CoV2 transmission routes become more clearly defined. Until then this takes a risk averse approach to reduce indoor pollution without significant capital expenditure
