Filter aerosol penetration. A Model 8130 Automated Filter Tester (AFT) (TSI, Inc., St Paul, MN, USA) was used to measure initial filter aerosol penetration for all post-decontamination and control FFR samples. All tests were conducted at room temperature with a continuous airflow of 85 -4 l min À1 in accordance with NIOSH certification test procedures (NIOSH, 2007) for challenging N-series filters, with two exceptions: all filters were tested for filter aerosol penetration without any relative humidity pretreatment or NaCl aerosol loading. Collecting the data in this manner allows consistency with previous work (Viscusi et al., 2007) . Filter aerosol penetration levels were determined using a Plexiglas test box as previously used and described by Viscusi et al. (2007) or an appropriately sized test fixture supplied by the respective FFR manufacturer, as was the case for models N95-C, SN95-D, and P100-H.