How your breath travels

You will have heard the phrase “coughs and sneezes spread diseases”, but just how does this happen? 

In this case study, you will explore the physical processes behind how respiratory viruses spread. Fluid dynamics plays a crucial role in understanding and mitigating disease transmission, as well as our exposure to air pollution. Since breath itself is a fluid, it follows the principles of fluid dynamics. Factors such as airflow, turbulence, and droplet behaviour determine how pathogens travel through the air and interact with their surroundings.

Let’s first pose the question: What are you breathing? 

You spend up to 90% of your time indoors, so most of the air you breathe comes from inside a building. This means that the majority of our exposure to pollutants occurs indoors—at home, in schools, workplaces, transportation, healthcare facilities, and social settings. 

Take a look at the diagram below to explore some of the different pollutants that we can be exposed to daily, even just through routine activities in our own homes. A full-text description is available in the Downloads.

As well as these pollutants, there is significant evidence that many diseases are spread through the air. This includes diseases caused by bacteria, such as tuberculosis (TB), as well as viruses, including measles, influenza and the virus that causes COVID-19. 

In this case study, you’ll explore the journey of a ‘contaminated’ particle that can cause infection. You will think about how these particles are generated by human respiration and released in a sick person’s breath and how they are transported through the air to expose other people in the indoor environment of a building. You will also explore how engineering measures such as ventilation can be used to reduce the transmission of disease and how understanding the fluid dynamics of indoor airflow can improve the design of such control measures.  

Have a go:

Let’s carry out an exercise: How far does your breath go? 

Test from how far away you can blow out a candle.

• How far before you can make the candle flame flicker? 
• How does this distance change if you blow very gently or if you blow hard?

Discuss your findings with other learners in the Comments.