With the continuous increase in the number of active COVID-19 cases in many countries, the inflow of patients in hospitals has been rising. Doctors and the healthcare staff are not only struggling to provide treatment to each and every patient but are also coping with the shortage of personal protective equipment (PPE) and N95 respirators. Once a PPE kit is removed, it cannot be used again, which leaves healthcare professionals with no choice but to wear the PPE kit for eight or more hours.
Amid the shortages in PPE and N95 masks, some healthcare systems have started adopting non-standard practices such as using expired N95 masks or decontaminating the masks to prolong their use.
Testing the effectiveness
PPE and N95 respirators are known to filter around 95% of the particles which are tinier than 0.3 micrometres. To test the quality of the masks, scientists from the University of North Carolina Health Care conducted a study between April and June 2020, where they tested the fitted filtration efficiencies (FFEs) of 29 different fitted face masks worn by a male and female candidates in a custom-built chamber with an aerosol generator in it. FFE refers to the efficiency with which the masks filter aerosol particles.
The study was published in the journal JAMA Network on 11th August 2020.
The temperature of the chamber during testing ranged from 23 degrees Celsius to 29.5 degrees Celcius and the relative humidity was 10 percent to 50 percent. The scientists used different masks such as Controlled Air Purifying Respirator system (MAXAIR), N95 masks (both expired and non-expired), surgical masks and other masks approved by the US Centers for Disease Control and Prevention (CDC).
The expired masks were treated with three respirator sterilisation methods: ethylene oxide, steam (at 121 °C temperature for 15 minutes) and vaporized hydrogen peroxide.
During the study, the candidates were asked to repeatedly move their torso, head, and facial muscles to recreate the typical occupational activities of the mask wearer.
Results of the evaluation
The result of the study showed that MAXAIR along with a face shield prevented more than 99 percent of particles from entering the candidate’s breathing space, while the N95 masks were able to reduce the entry of particles by more than 97 percent.
The expired N95 respirators (up to 11 years past their expiration date) which had intact elastic straps and were sterilised with ethylene oxide and hydrogen peroxide showed more than 95 percent FFEs. However, this ability reduced to 90 percent to 95 percent when the person was given a wrong sized N95 respirator.
The researchers further found that after steam sterilization, 3M 1860 N95 respirators (a type of N95 mask) got distorted and could not be used again, while 3M 1870+ Aura face masks were able able to retain more than 95 percent FFE. Moreover, none of the imported respirators approved by the CDC achieved 95 percent FFE.
The scientists concluded that expired N95 respirators and sterilised old N95 respirators can be used in the absence of new N95 respirators. However, the use of other alternatives such as surgical masks and other respirators may not be able to provide equivalent protection from the aerosols.
For more information, read our article on How useful are masks against COVID-19 and how to use them.
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