Thread by @claire_horwell

Short🧵on healthcare facilities insisting on the public swapping #N95/#FFP2 #masks with surgical masks on entry. I have heard of this happening in @NHSuk too. Is it a ridiculous request? 1/

https://twitter.com/DavidElfstrom/status/1470568048562159616

2/ I assume that the reason healthcare facilities insist on this is to ensure that people do not enter the facility with contaminated masks and that, for the majority of the public, who are wearing cloth masks, or don't have a mask, a surgical mask will provide better protection.

3/ Let's look at filtration efficiency: #N95/#FFP2 masks are certified to be 95% efficient at capturing particles of 0.3 micron diameter. Surgical masks do not have that certification.

4/ However, surgical masks are also made of non-woven material and our filtration tests (using PM2.5, not virus particles) showed #N95 masks had ~99% efficiency and surgical masks had ~88%. Not as good but not terrible. sciencedirect.com/science/articl…

5/ The other major factor in mask effectiveness is fit. If a mask with excellent filtration efficiency is loose on your face, it may offer no better protection than a well-fitting surgical mask. sciencedirect.com/science/articl…

6/ One problem is that #N95 masks come in many shapes. The best ones - used in occupational settings - have head straps rather than ear loops and these are much more likely to tightly seal to the face. So, if your mask fits badly, it won't be very effective.

7/ Surgical masks are designed to capture large droplets emitted from healthcare workers' respiratory systems. They are not designed to prevent inhalation of airborne aerosols so they are not designed to seal around the face, but they can fit some faces well. #COVIDisAirborne

8/ Back to the original question - is it wrong for healthcare facilities to insist on the public swapping #N95 masks for surgical ones? Ethically, I think it is wrong to ask people to swap a more effective public health intervention with a less effective one.

9/ Maybe it's about equality - ensuring everyone has the same opportunity for protection. I could understand that.
Maybe it's about preventing contamination? I don't think so as the public are not asked to put on full PPE so their clothes etc. could also contain a viral load.

10/Maybe it's not an evidence-based decision. Unfortunately, it's not easy to find that out. My advice is that you ask if you can retain your #N95 but, if the answer is no, fit the surgical mask as best as you can to your face. The level of protection may not be vastly different.

11/ Our research showed that fit of surgical masks can be improved by adding an additional layer of thin cloth, tied around the head. Consider taking a thin scarf with you? sciencedirect.com/science/articl…

12/ Note: these are my personal opinions, without having information behind the decisons by healthcare facilities. I hope maybe healthcare facilities can comment on why they insist on the public swapping their own industry-certified masks for the facility's surgical ones.

13/ If you want to learn more about #facemasks for #COVID19, and their effectiveness, please check out @trishgreenhalgh's excellent thread:

https://twitter.com/trishgreenhalgh/status/1414294003479089154?s=20

14/ Lots of people saying they've added a surgical on top of N95, when asked to remove the N95. Advice: put it on loosely; a tight fitting surgical mask on top of an N95 may substantially increase breathing resistance (how hard it is to breathe through the masks).