INTRODUCTION:
Global infection of SARS CoV-2 caused a disease called Corona-virus Disease 2019(CoVID-19) with a Chinese city, Wuhan as its epicenter. To attenuate the effect of SARS CoV-2 infection, the World Health Organization (WHO) issued guidelines according to which to prevent the spread of infection and for personal protection face masks are mandated. This led to a shortage of commercial supplies. To follow the guidelines and for personal protection, people started using different face covers like homemade masks, bandanas, hankies, etc. With the use of these different face coverings, a major concern about their efficacy of filtering the droplets during cough, sneeze, and speech come into play. Fischer et al demonstrated a simple optical measurement method to evaluate the efficacy of masks to reduce the transmission of respiratory droplets during regular speech. This measurement method is cost-effective and no expert is required for it to work.
We talk of a huge range when we use the world facemask or face cover and that range varies from hankies to N95 masks and many more. The initial application of face mask was to protect the surrounding individuals from the wearer but nowadays face masks are commonly used to protect the wearer from surrounding as an example pollution mask. The government used this application and mandated the use of a face mask as a personal protection gear. But due to several reasons including availability, long-wearing duration, breathability, and physical appearances people shifted to more comfortable and convenient options of unknown efficacy. The filtering efficacy of 14 different varieties of masks(Figure 01) varying from N95 respirators to bandanas was demonstrated using this measurement method.
Figure 01: Pictures of masks used in the demonstration.
Source: DOI 10.1126/sciadv.abd3083
MEASUREMENT METHOD
Apparatus design:
The major component of the apparatus includes a phone camera, a laser source, and an enclosure with openings of different measurements. As the demonstration is light-based so to eliminate the outside light enclosure was made from black material. The enclosure has slits on two parallel sides for entry and exit of the laser. On both adjacent sides, circular holes are made, one for the camera and one for the speaker. The hole made is of the size that allows the flow of droplets without the speaker interfering with the laser. On top HEPA filters are fitted to continuously blow air and prevent the entry of unwanted particles by creating a positive pressure.
The apparatus is assembled(as shown in Figure 02), the traversed light enters the enclose from a circular mirror fitted just before it. The speaker speaks which results in exposure of droplets passed face cover. The exposed droplet then scatter the laser rays and this scattering is recorded in the phone camera till the droplets get cleared along with a few seconds before the speech and during the speech. Then the video containing the scattering by droplets is analyzed by using “Mathematica”(other commercial packages can also be used). This demonstration performed repeatedly for every face cover to get a better result.
FINDINGS
The demonstration yields the information(Figure 03) that the best face cover to use is fitted N95 masks with almost nil relative droplet count. And the worst face-covering in terms of filtering efficacy are Bandanas and Fleece with a relative droplet count of 0.2 to 1.0 and 0.7 to more than 1.
The other good and effective face coverings are surgical masks, Poly/Cotton masks, and Polyprop masks.
The valved N95 mask stood 8th in the demonstration with a relative droplet count of 0.1 to 0.2.
DISCUSSION
There are few limitations to this demonstration including the number of repetition performed, the number of individuals with which the demonstrations performed as mask fitting and size may vary individually, the size of the enclosure as the opening used for the speaker can alter the droplets exposure and lastly the video recording device as this limits the visuals of the scattered light a better device might show variation in the observation. But using the apparatus mentioned the results came out to be satisfactory.
I will conclude by suggesting to wear a fitted N95 mask or surgical masks because wearing a bandana and fleece is exactly similar to wearing nothing.
REFERENCE
Emma P. Fischer, Martin C. Fischer, David Grass, Isaac Henrion,Warren S. Warren and Eric Westman Low-cost measurement of facemask efficacy for filtering expelled droplets during speech DOI: 10.1126/sciadv.abd3083