A seal check (the procedure you mentioned) can’t replace a fit test. For maximum protection, full-face respirators like the Narwall seem to require a quantitative fit test to be performed (rather than a qualitative fit test which is performed using a nebulizer). Unfortunately, the Narwall isn’t designed for the quantitative test, and so, it can’t be fit tested.
A seal check (the procedure you mentioned) can’t replace a fit test. For maximum protection, full-face respirators like the Narwall seem to require a quantitative fit test to be performed (rather than a qualitative fit test which is performed using a nebulizer). Unfortunately, the Narwall isn’t designed for the quantitative test, and so, it can’t be fit tested.
https://tsi.com/getmedia/3d247f13-bb31-4ec5-921b-92aa6360cc4c/ITI-032?ext=.pdf
https://www.youtube.com/watch?v=2xyNg2s1u7c