Author contributions
S Darby, K Chulliyallipalil performed the experiments. S Darby, M Przyjalgowski, P McGowan built the system. S Darby, K Chulliyallipalil, S Jeffers, A Giltinan, N Smith and RD Sleator analyzed the data. S Darby and RD Sleator wrote the manuscript. RD Sleator, N Smith and L Lewis supervised the project. All authors reviewed the manuscript.

Acknowledgments
The authors gratefully acknowledge support from Andor Technology (Belfast) for the loan of the Sona sCMOS camera platform for a large field of view and low light imaging. The authors also acknowledge the ASSERT training centre of University College Cork for the loan of the dummy.

Financial & competing interests disclosure
Authors S Darby, A Giltinan, N Smith and RD Sleator are members of the National Standards Authority of Ireland (NSAI) expert advisory group on face coverings contributing to SWiFT 19 and CWA 17553. S Darby is also a member of CEN/TC248/WG38 on face coverings. This work was funded by Science Foundation Ireland under the SFI COVID-19 Rapid Response Funding Call (proposal ID 20/COV/0253). The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.
No writing assistance was utilized in the production of this manuscript.