Thread by @claire_horwell

Short 🧵to address this comment. The public do not need to be fit tested in order to wear an FFP3/N99 or FFP2/N95 mask. Here's why: 1/

2/ Fit testing is a procedure which employers are legally obliged to undertake to ensure the safety of workers in dusty industries. It ensures that respirators fit so that workers are protected from the constant exposure to potentially toxic dusts, that they receive over a shift.

3/ Whilst it would be great to fit test the public, it is not practical or possible. Nevertheless, FFP2/3 N95/99 masks are widely used, especially in humanitarian crises, by the public and are even donated by major mask manufacturers, for public use, during these crises.

4/ It is correct that if you don't wear a certified mask properly, or if it is not a good fit to your face, then it will not be as protective as it could be. But it is not correct that it offers no more protections than a surgical mask.

5/ Pre-covid, we conducted tests on FFP2 & surgical masks, for community use during 🌋ash exposures. We found that, with no fit training or testing, FFP2 masks were still much more effective at filtering PM2.5 (tiny particles) than surgical masks. sciencedirect.com/science/articl…

6/ This is because FFP2/N95 masks are designed to make a close seal to the face, in the first place. Surgical masks are not. BUT, you may need to try on a few masks to find the one that fits your face shape best. And you need to follow instructions on how to wear it properly.

7/ For my 🌋project, we made a video to demonstrate how to fit #N95 and other masks, because it's important for these #facemasks to fit correctly.

8/ We also made a leaflet: ivhhn.org/information/pu…

9/ Until now, there was an ethical question as to whether the public should deplete resources required for healthcare etc.
18 months into this pandemic, my opinion is that there has been adequate time for governments to secure supply chains, if they choose to do so.

5.5/ Meant to add in this tweet from @trishgreenhalgh reporting lab studies with artificial respiratory aerosol:

10/ And manufacturers have hugely increased capacity.

The point is that fit testing checks fit. But, you can get a very good idea yourself by following instructions and checking if you can feal leakage of air around the edge of a mask, and adjusting fit/trying different masks.