2.4. Filtration Test
The filtration performance of respirators was evaluated using an automated filter tester (TSI 8130, TSI Inc., Shoreview, MN, USA), using NaCl particles (mass median diameter, MMD ~0.6 µm) and paraffin oil aerosol (MMD ~0.4 µm), based on the Korean MFDS standard. NaCl aerosol with a mass concentration of 8 ± 4 mg/m3 or paraffin oil aerosol with a mass concentration of 20 ± 5 mg/m3 was passed through the respirator sample at the flow rate of 95 LPM. The aerosol penetration after 3 min of challenged aerosol mass and the initial resistance were recorded as performance criteria.