Ventilation and indoor transmission of airborne infections

Many were infected at home

During the pandemic, experience has shown that many people became infected in their own homes. Our existing buildings and ventilation systems are not built to protect us from the spread of airborne infections. To reduce the spread of indoor infections in the future, the situation needs to be improved.

The project aims to improve ventilation

The project is based on refurbishing and supplementing existing ventilation and the overall practical aim of the project is to develop measures that will provide greater protection against the spread of infection. The spread of infectious agents is reduced both within and between rooms by changing the airflow pattern. The effect of the measures is reported as a reduced risk of infection after the measures have been implemented.

Existing systems are not sensitive enough

At present, there are no precise models for estimating the risk of becoming infected indoors depending on how the ventilation of the building is arranged. The models are simply too insensitive to make good estimates.

Improved model

A completely new approach to how we reduce the spread of air between rooms and how pollutants are transported away is developing an improved model for estimating the risk of becoming infected. The project is a collaboration with Japanese researchers from Kasuga and Saitama Universities.

The new approach considers the air and the contaminants as two populations:

• One of the populations leaves the room never to return and is therefore ventilated away. The capacity of the removal ventilation is not always the same as the supplied ventilation airflow but equal to the purifying flow which can vary from almost zero to equal to the ventilation airflow.
• The second population consists of air and contaminants that recirculate to the room and spread the contaminants.

The risk of spread from an infected person to different parts of the room and between rooms is determined by measuring the probability of transmission. The pathway of the infectious agent between the infected person and to different parts of the building is also recorded.

By knowing the routes of infection, it is possible to identify zones where people can become infected. When the capacity of the ventilation system is not sufficient, this leads to the re-entry of infectious agents into the room. The frequency of visits is a measure of the spread of the infectious agent. When it increases, the probability of being infected is higher.

Experiments in the laboratory

Through full-scale experiments and simulations in the laboratory at the University of Gävle, the airflow has been studied in terms of different parameters. Sealing of building elements is one method to protect against spread. This measures the relationship between the probability of transmission of infection in relation to the difference in pressure in the building. This makes it possible to set requirements for the tightness of the building in order to reduce the probability that the infection will remain in the room.

The practical measures to reduce the risk of transmission can be implemented for use for a limited time and then reset. The alternative is to carry out a permanent refurbishment. The experience of the current pandemic may lead to future requirements for pandemic-friendly construction. This project can contribute to the design of such buildings.

The results of the project will be presented as a chapter in a book on ventilation.