Adding an external procedure mask in front of a filtering face-piece respirator (FFR), such as an N95, has been suggested at times, largely to protect the FFR from soiling and to extend its use. One hundred healthcare workers from Mayo Clinic in Arizona, who successfully passed quantitative fit testing of an N95 respirator (3M 1870 Aura FFR), were immediately re-evaluated to assess the effect of adding a procedure mask (Halyard 47117) in front of their N95. Thirteen out of 100 participants failed the quantitative fit test following the addition of the procedure mask. Authors review potential causes as well as limitations of the study with regard to testing a single combination of face protection devices. Guidance on the use of N95 FFRs should consider the potential risk of increased fit failure when they are worn with an overlying face mask. Further research including other FFR + face-mask combinations is needed.

https://iars.box.com/s/295vnv4nob7s9jsvsmjj4ypqpqi7cayr