Using widely available tools, scientists have developed a simple method to visualise how effectively different types of masks prevent the spread of droplets that could contain novel coronavirus particles, an advance which could aid small scale mask producers to optimise designs, and help community outreach organisations demonstrate proper mask fitting procedures.
The technique, described in the journal Science Advances, is still in the early stages, and has so far only been tested in a small group of people, the scientists said.
According to the researchers from Duke University in the US, the preliminary, proof-of-principle findings suggest that professional-grade N95 masks, surgical or polypropylene masks, and handmade cotton masks may all block much of the droplet-spray produced when wearers speak.
However, they said bandanas and neck fleeces likely provide little protection, as the scientists observed that more droplets are expelled through these materials.
They said this is likely because the materials break up larger droplets as they pass through the material.
In the study, the scientists evaluated the effectiveness of 14 different types of masks and other frequently substituted face coverings, using a simple approach in which either one male speaker or, in some cases, four speakers wore each mask while standing in a dark enclosure.
The speaker then uttered the phrase "stay healthy, people" five times in the direction of a laser beam, which scattered light from the droplets released during speech, the study noted.
A cell phone camera recorded the droplets and a simple computer algorithm counted them, the scientists added.
The setup, intentionally designed to be simple and inexpensive, can be replicated by non-experts, according to the researchers.
They said the hardware it requires, including laser equipment, is commonly available and can be purchased for less than USD 200.
While the researchers acknowledge the need for further testing, they suggested based on the findings that N95 masks without valves blocked droplet spread best, and surgical or polypropylene masks and handmade cotton face coverings were also effective.
But the early findings suggested that bandanas and neck fleeces do not provide protection.
"Our work was a demonstration of a simple measurement method, not a systematic mask study," noted Martin Fischer, the study's corresponding author.
"More work is required to investigate variations in masks, speakers, and how people wear them. We also want to extend our method to other droplet-generating actions, like coughing and sneezing. Further, we want to explore effects of incorrect placement and moisture saturation," Fischer said.