Written By: Longjam Dineshwori | Updated : September 24, 2020 8:56 AM IST
Using face masks in combination with social-distancing and frequent hand-washing is globally accepted as the most effective way of combating the spread of COVID-19. However, many people are also using plastic face shields as an alternative to regular cloth or surgical masks. While face shields may be more comfortable than regular masks, there is a doubt over the effectiveness of these alternative options in preventing the spread of the novel coronavirus.
A recent simulation by Japanese researchers using Fugaku, the world's fastest supercomputer, found that plastic face shields are almost totally ineffective at trapping respiratory aerosols. Fugaku detected that almost 100% of airborne droplets of less than 5 micrometres in size escaped through plastic visors that are often used by people working in service industries. In addition, about 50 per cent of larger droplets measuring 50 micrometres found their way into the air, according to Riken, a government-backed research institute in the western city of Kobe.
Based on the results of the simulation, Makoto Tsubokura, team leader at Riken's centre for computational science, has cautioned against wearing face shields as an alternative to masks.
Tsubokura told the Guardian that the effectiveness of face guards in preventing droplets from spreading from an infected person's mouth is limited compared with masks.
According to Tsubokura, almost all small droplets of less than 20 micrometres can escape through the gap between the face and the face shield. But it could block droplets larger than 50 micrometres.
People who are advised not to wear masks, such as those with underlying respiratory problems and small children, could wear face shields instead, but only outdoors or in indoor settings that are properly ventilated, Tsubokura suggested.
Fugaku also found that face masks made from non-woven fabric are more effective at blocking the spread of Covid-19 via airborne droplets than those made of cotton and polyester.
Several studies have also cautioned against the use of masks equipped with valves after it was found that a large number of droplets can pass through the exhale valve unfiltered. So experts suggest using a good quality cloth or surgical masks that are of a plain design, instead of face shields and masks equipped with exhale valves to minimize the community spread of COVID-19.
Researchers from Duke University in the US recently came up with a simple method to test the effectiveness of different types of masks in preventing the spread of coronavirus particles. The technique described in the journal, Science Advances uses laser equipment, a cell phone camera to record the droplets and a simple computer algorithm to count them. Using this method, the scientists evaluated the effectiveness of 14 different types of masks and other frequently substituted face coverings, such as bandanas and neck fleeces.
They found that N95 masks without valves were best at blocking the droplets produced when wearers speak. Surgical or polypropylene masks and handmade cotton masks were also effective in blocking droplet spread. But they show more droplets expelled through bandanas and neck fleeces, suggesting that these materials may provide little protection against the novel coronavirus. One possible reason is that the materials use to make bandanas and neck fleeces can break up larger droplets as they pass through them, they explained.
