1/ I feel a need to explain this further: All NIOSH-approved N95 NEED to be fit tested! This is an requirement of the US standard: 42 CFR 84. The standard itself is missing one crucial test that is present in all other standards - Total Inward Leak (TIL)

2/ TIL is basically a test of actually fitting the mask onto a number of subjects with different facial dimensions and then getting them to do a set of activities including moving your head, walking and talking. This is similar to the activities during fit testing...

3/ This means that N95 masks might be good at filtering particles, but do not need to actually fit anyone’s face.

In theory I could design a cup twice the size of a person’s face and it will still pass the required tests to get NIOSH approval...

4/ NIOSH tried to update the standard in 2009-2010, but this was rejected after petition by ISEA. Remember that this was a measure that would IMPROVE the safety of workers... https://safetyequipment.org/knowledge-center-items/total-inward-leakage-testing-for-respirators/

5/ Subsequent research has demonstrated that some N95 masks are simply impossible to fit. The following table was adapted from Rengasamy et al, 2014. which demonstrated that most test subjects failed in respirator designs A, C & D.

6/ This is why in the US, OSHA mandates that any worker who wears a respirator must undergo fit testing under 29 CFR 1910.

Because without fit testing, there is no evidence that your N95 mask is working to protect you. @DrJulieAMiller @rajah_mich @enenbee