What is the optimal time for face coverings to mitigate transmission?

Respirator masks have been hailed the go-to face covering to mitigate COVID-19Respirator masks have been hailed the go-to face covering to mitigate COVID-19.

Researchers at the University of Surrey recommend the masks are worn between 3.2 and 9.5 hours for ‘maximum effectiveness’ – suggesting a level of around 97% effectiveness against virus-laden particles.

Medical face masks provided between 2.6 and 7.3 hours of usage time, with around 81% effectiveness.

They also revealed that handmade masks are effective for around four to 8.8 hours. However these are only 47% effective.

Respirator mask usage

Carried out by Surrey’s Global Centre for Clean Air Research (GCARE), they wanted to answer two questions:

  1. How long a mask should be worn
  2. When it should be discarded, recycled or washed to optimise its usage time.

The team carried out a thorough laboratory investigation on 11 masks*, and found that over time the filters of a face covering start to get clogged by aerosol particles.

Breathing resistance also increases with mask usage. It is the crossover point between particle penetration and breathing resistance estimates an ideal usage duration.

Clear and accurate

Professor Prashant Kumar is a senior author of the paper and founding director of GCARE at the University of Surrey.

He said: ‘It is important to reiterate that while vaccination is key to the fight against COVID-19, face coverings are also essential.

‘Donning a face mask is not only about protecting yourself but all those around you.

‘While any face mask is better than no face mask, our research aims to give the general public clear and accurate information so they can make informed decisions as we continue in our fight against COVID-19.’

*A simplified description of 11 types of face protective equipment – four respirators; three medical; and four handmade in the submicron range.


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