Our preference for ventilated spaces is a preference for dilution ventilation. That is, the concentration of pathogen-laden aerosolised droplets in the air will drop if we allow outside air to ‘dilute’ the air within the room and decrease the probability of infections.

In 1957, researchers established this empirical relationship between infection probability and air diffusion with guinea pigs supplied air drawn from a tuberculosis ward. This work led to the Wells-Riley equation, which researchers have tweaked and improved over the years and have used it to develop subsidiary models, like the Rudnick-Milton model. And these models together imply that a building must have appropriate opportunities for air from the outside to diffuse inside and have large volumes of space in which the air can mix.

Comfort in buildings shouldn’t, and doesn’t, have to come in exchange for a heightened risk of spreading airborne pathogens. COVID-19 has put indoor ventilation in the spotlight, among other things, and architects, urban planners and healthcare workers thus have an opportunity to use this intervention to help fight the spread of tuberculosis, measles, influenza and other airborne diseases.

Raja Singh is a PhD research scholar and Anil Dewan is professor – both at the department of architecture, School of Planning and Architecture, New Delhi.