New Indian study finds out how effective face masks can be

What are some of the things you have noticed about how face masks are worn? Possibly, the fact that they don’t always cover the mouth and nose properly. Some masks hang around the chin, others don’t even cover the nostrils, defeating the purpose of wearing one.

In new findings published in the journal Physics Of Fluids, researchers from the Indian Space Research Organisation (Isro) and Sri Jayadeva Institute of Cardiovascular Sciences and Research in Bengaluru have experimentally visualized the “flow fields of coughs" in common mouth-covering scenarios.

Padmanabha Prasanna Simha, from Isro, and Prasanna Simha Mohan Rao, from the Sri Jayadeva institute, used a technique called Schlieren imaging—a visual process that photographs the flow of fluids of varying density. They also leveraged the intricate link between density and temperature—coughs tend to be warmer than their surrounding area—to capture pictures of voluntary coughs from five test subjects. According to an official news release, by tracking the motion of a cough over successive images, the team was able to calculate the velocity and spread of the expelled droplets.

The imaging led to some interesting findings. For instance, Simha and Rao found N95 masks to be the most effective at reducing the horizontal spread of a cough. N95 masks or respirators offer one of the tightest fittings, which make them an important element in personal protective equipment for healthcare settings. “The N95 masks reduced a cough’s initial velocity by up to a factor of 10 and limit its spread to between 0.1 and 0.25 meters," the release adds.

Schlieren images of coughs with varying degrees of face covering. (Credit: Padmanabha Prasanna Simha, Indian Space Research Organisation)

On the other hand, without a mask, a cough can travel up to 3m. Even a simple disposable mask can bring this down to 0.5m, the findings show. “Even if a mask does not filter out all the particles, if we can prevent clouds of such particles from traveling very far, it’s better than not doing anything," Simha says in the release. “In situations where sophisticated masks are not available, any mask is better than no mask at all for the general public in slowing the spread of infection," he adds.

As the Schlieren images show, the experiment was repeated to visualize the spread in other scenarios: a user covering their face with a surgical mask, one hand, cupped hands, a folded handkerchief or their elbow. The findings from the elbow example were particularly striking. With the covid-19 pandemic still rampant, health organizations around the world have recommended coughing into your elbow in the absence of a mask or face covering. But the findings show that a bare arm—not covered by a sleeve—cannot form a proper seal and obstruct airflow. “A cough is then able to leak through any openings and propagate in many directions," the release adds.

While these findings reaffirm the importance of masks, and wearing them in the right manner, the researchers stress the importance of adhering to social distancing measures. “Adequate distancing is something that must not be ignored, since masks are not foolproof," Simha says in the release.