COVID-19 and tuberculosis spread through the air. A person who sneezes, coughs or talks in an enclosed space without a mask, puts others in the room at risk of sharing the air that they have exhaled. This air contains microscopic droplets that contain the disease-causing pathogen.

So the measures we put in place and habits we adopt to deal with COVID-19 could in fact help our response to measles, influenza and tuberculosis as well.

Good ventilation has always been considered a virtue for buildings, as has copious sunlight indoors. However, builders don’t always consider improving access to sunlight and ventilation in their designs. Most office buildings today are centrally air-conditioned with large unopenable glass panes – thanks to the focus on providing thermally comfortable built-spaces. There’s no inlet for outside air; the central AC system has a provision for outside air to enter the space but due to efficiency concerns, this supply is limited.

To repeatedly cool outside air before supplying it to the inside requires more energy. A more economical way is to recirculate the same air over and over again. This saves energy, for sure, but at the risk of exposing occupants to airborne infections.

This problem is worst in rooms that use split ACs. These machines have narrow copper pipes to transport the refrigerant between the indoor and outdoor units. The indoor unit supplies cool air and keeps the occupants comfortable. But this air is also constantly recirculated. There is no provision to transport fresh air from the outside to within the room.

Our general lack of awareness also means we close the windows and the doors to seal in the cool air and reduce power consumption. A better scenario would be one where the room has some leaks – like cracks under the doors and around window frames – through which air from the outside can enter the enclosure.

Up Next: Some background on the relationship between infection probability and air diffusion