The smallest respiratory drops are filtered through a face mask constructed from a folded scarf. Despite the leak, the spread of the drops is significantly hampered compared to use without a mask. Credit: Siddhartha Verma, Manhar R. Dhanak, and John Frankenfield
Mannequin simulated coughs and sneezes show increased efficacy in well-fitting, multi-layer fabric masks.
While the use of face masks in public has been widely recommended by public health officials during the current period COVID-19 In the event of a pandemic, there are relatively few specific guidelines regarding mask materials and designs. A study by Florida Atlantic University, in the Fluid Physics, from AIP Publishing, seeks to better understand which types are best for controlling respiratory drops that could contain viruses.
Siddhartha Verma and her team experimented with different material and design options to determine how well facial masks block drops when they leave the mouth. Using a laser to detect drops while coughing and sneezing from a mannequin’s head, the group was able to trace the paths of the drops and examine how different designs and materials alter that path.
The authors point to the need for additional quantitative analysis, but were aware of the power of more direct visualization.
“While there are some previous studies on the effectiveness of medical grade equipment, we don’t have a lot of information on fabric-based coatings that are most accessible to us today,” said Verma. “We hope that the visualizations presented in the document help convey the rationale for the recommendations for social distancing and the use of face masks.”
The approach is based on a laser blade setup that is a mainstay for those studying fluid mechanics, which Verma compares to seeing dust particles in a beam of sunlight.
“The main challenge is to represent the cough and sneeze faithfully,” he said. “The setup we have used is a simplified cough, which is actually complex and dynamic.”
The group found that slightly folded face masks and bandana-style covers reduced the distance traveled by the drop jets by 1/8 to 1/2 respectively of that for an uncovered cough. However, well-fitting home masks with multiple layers of quilted fabric and standard cone style masks proved to be the most effective. Despite some leaks, these masks significantly reduced the number of drops.
When unmasked, mannequins sprayed droplets much farther than the 6 feet frequently cited in the social distancing guidelines.
Verma said the group seeks to continue studying the complex interaction that droplet evaporation, ambient air flow, and the properties of expelled respiratory fluid that lead to how droplets behave can involve.
“It is also important to understand that facial coatings are not 100% effective in blocking respiratory pathogens,” he said. “That is why it is imperative that we use a combination of social distancing, facial covering, hand washing, and other recommendations from health care officials until an effective vaccine is released.”
Read Comparison of the effectiveness of face mask in mitigating COVID-19 transmission for more information on this research.
Reference: “Visualizing the effectiveness of face masks in obstructing the breathing jets presented” by Siddhartha Verma, Manhar Dhanak and John Frankenfield, June 30, 2020, Fluid Physics.
DOI: 10.1063 / 5.0016018
