Measuring the filtration performance of breathing system filters using sodium chloride particles*

The filtration performance of 33 breathing system filters (nine pleated hydrophobic and 24 electrostatic filters) was measured using sodium chloride particles. The particles had a size distribution with a count median diameter of 0.07 microm and a geometric standard deviation not exceeding 1.83. The geometric mean penetration values ranged from 0.002 to 0.67% for the nine pleated hydrophobic filters and from 0.25 to 35% for the 24 electrostatic filters (p < 0.0001 for the difference between the two filter types). The filtration performance obtained when filters are challenged with either sodium chloride particles or microbes is compared and discussed.