New research reveals additional guidelines for wearing masks- WHO
—masks must have three layers for effective protection
DPI, Guyana, Saturday, June 6, 2020
The World Health Organization (WHO) on Friday updated its guidance and recommendations on the wearing of masks in public for protection against the novel coronavirus (COVID-19).
Director-General of WHO, Dr. Tedros Adhanom Ghebreyesus said the updated guidelines are based on new research carried out by the organisation.
“WHO has developed guidance through a careful review on who should wear a mask and what it should be made of […] through careful review of all available evidence and extensive consultation.”
According to the study, when it comes to non-medical fabric masks three main factors were considered and tested: initial filtration, breathability and filter quality.
Researchers found that cloth fabrics have filtration of 0.7-60 percent. The higher the filtration efficiency, the better the protective barrier. While breathability, which can be measured in Pascals (Pa) should be below 100 Pa.
Materials with the highest initial filtration were cotton, polyester and bonded tissue paper. Knitted cotton fabric was found to have a higher filtration efficiency than woven cotton, while bonded toilet tissue paper made of cellulose proved to be higher than cotton.
Depending on the fabric used breathability and filtration can complement or work against each other when determining the overall filter quality of cloth masks. The least overall filter quality recommended by the experts was said to be 3.
Cotton has an overall filter quality of 5.4-7.6 percent, while polyester was 6.8 percent and polypropylene 16.9 percent.
Among its recommendations for wearing masks, WHO stated that cloth masks should have no less than three layers to prevent transmission of the virus.
Masks made of cotton handkerchiefs with 4 layers only achieved 13 percent efficiency, and porous materials such as gauze, even with multiple layers will only provide 3 percent filtration efficiency.
According to the WHO’s layout for the three-layered masks, the innermost layer should be made of a hydrophilic (attracted to water) material such as cotton or cotton blends.
The second or middle layer should consist of a hydrophobic (repelling water molecules) synthetic non-woven materials like cotton or polypropylene to enhance filtration or retain droplets.
Finally, the outermost layer should be made of hydrophobic material such as polypropylene, polyester or their blends which can limit contamination from penetration to the nose and mouth.
Masks should be flat-fold or duckbill shaped or designed to closely cover nose, cheeks and chin for adequate protection.
While contents such as wax, may increase barrier protection, the WHO is heavily against it, as it can block pores, decreases breathability and cause unfiltered air to escape at the sides when exhaling.
Dr. Ghebreyesus also called on governments to “encourage the public to wear masks where there is widespread transmission and physical distancing is difficult, such as on public transport, in shops or other confined or crowded environments.”
The WHO also recommends a medical mask to be worn by all clinical and healthcare workers even when there is no COVID-19 confirmed case. Persons over 60 should wear masks to prevent community and other forms of transmission.
Persons must also remember that masks on their own will not offer protection and to follow all other guidelines including social distancing.