WASHINGTON — All over the country Americans are being told to stay safe by maintaining a six foot distance from one another in public settings. Unsettlingly, a new study finds that those suggestions may be very insufficient. There is still a lot we don’t understand about the airborne transmission of the coronavirus, but researchers have found that just a slight 2.5 MPH breeze can propel saliva 18 feet in five seconds!
“The droplet cloud will affect both adults and children of different heights,” comments study co-author Dimitris Drikakis in a release by the the American Institute of Physics. “Shorter adults and children could be at higher risk if they are located within the trajectory of the traveling saliva droplets.”
Whenever anyone coughs, saliva is inevitably released and travels through the air in a suspended state. Of course, the distance saliva travels depends on a number of factors; the size and amount of droplets, how the droplets are interacting with one another, rate of evaporation, the transference of heat and mass, and air conditions (humidity, temperature).
To study saliva movements through the air, the research team created a computational fluid dynamics simulation. That simulation is capable of analyzing the characteristics of every single saliva droplet traveling through the air via a cough. The simulation also accounts for additional factors like dispersion force, humidity, saliva / air molecule interactions, and the transition of droplets from liquid to vapor.
The simulation is displayed on a computer as a grid that represents the entirety of space in front of a coughing person. The analysis for this study encompassed 1,008 saliva droplets and roughly 3.7 million subsequent equations.
“Each cell holds information about variables like pressure, fluid velocity, temperature, droplet mass, droplet position, etc.,” co-author Talib Dbouk says. “The purpose of the mathematical modeling and simulation is to take into account all the real coupling or interaction mechanisms that may take place between the main bulk fluid flow and the saliva droplets, and between the saliva droplets themselves.”
Again, these findings are by no means conclusive, but they certainly suggest that COVID-19 is quite capable of spreading well beyond the recommended six feet distancing guidelines. Further research on this matter should focus on the possible influence of ground surface temperatures on saliva behavior, as well as differences between indoor and outdoor environments. Air conditioning in buildings and homes can significantly alter the movement of aerial particles.
“This work is vital, because it concerns health and safety distance guidelines, advances the understanding of spreading and transmission of airborne diseases, and helps form precautionary measures based on scientific results,” Drikakis concludes.
The study is published in Physics of Fluids.
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