TU Delft: Delft researchers unmask millions of unsafe face masks

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.

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.


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.

Global Impac
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.

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