Delft researchers unmask millions of unsafe face masks

News - 16 September 2021 - Webredactie 3mE

Since the beginning of the coronavirus crisis, large numbers of medical face masks for healthcare workers have been imported. As there have been many different suppliers, the quality of these face masks has varied greatly. At the request of medical professionals, researchers at TU Delft developed a test method to check whether imported face masks met the safety requirements. And that was necessary, as it turns out, because in total only one-third of the 140 million face masks tested in 19 hospitals passed the safety test. The study and the results were published this week in the scientific journal PLOS One. 

Left Tim Horeman and right Bart van Straten

Test method

In March 2020, Delft researchers Tim Horeman, John van den Dobbelsteen and Bart van Straten, in collaboration with Greencycl, developed a method to sterilise face masks for reuse. Their method also proved to be a good way to check imported masks. It wasn’t long before the PFE test became the unintended standard for Dutch hospitals, which required providers to have this test performed. 

As a result of our research results, fears of false safety grew among medical professionals. Because the certification did not match the quality, doctors said they would rather reuse used face masks than the new batch of imported masks.

Tim Horeman, assistant professor at the Department of BioMechanical Engineering TU Delft

Unreliable certification

In Horeman and Van Straten’s study, they randomly tested 140 million face masks at 19 hospitals. This revealed that, despite being new, a very high percentage of imported face masks from 471 different suppliers fell far short of the PFE standard. In some batches, the quality of the filters in a portion of the face masks was sufficient, whereas in another portion the quality was far below the legal guideline. This means that some new masks offer little or no protection against virus particles and the certification often does not match the real quality.

Repackaging face masks after being sterilised. Copyright: TU Delft

The fear among healthcare workers increased rapidly because this is precisely the group that came into contact with COVID-19 patients. Soon, there were face masks with initials of doctors, with the request to return the same mask after sterilisation because they no longer trusted new masks.

Bart van Straten, PhD student in the Department of BioMechanical Engineering

Global Impact

The scope of this study and the startling results have led to rectifications, policy changes and new standards regarding the purchase of face masks. Based on this data, a new NEN standard is in the making for the safe reuse of disposable devices in times of crisis, and the test method has been adopted by healthcare institutions worldwide. In addition to the many hospitals in the Netherlands, healthcare institutions in South Africa were warned not to purchase half a million bogus face masks.

For questions & information

Tim Horeman: +31 15 27 85097,
Bart van Straten:
Dimmy van Ruiten, press officer TU Delft: +31 15 27 81588,


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