Chen C C, Lehtimäki M, Willeke K
Department of Environmental Health, University of Cincinnati, OH 45267-0056.
Am Ind Hyg Assoc J. 1993 Feb;54(2):51-60. doi: 10.1080/15298669391354324.
Most filtering facepieces used today are made of electret material (material with significant electrical charges on the filter fibers). Because of the addition of this electrical removal force, the filtration efficiency can be significantly increased without increasing the air pressure drop inside the respirator; pressure drop is closely related to physiological load. However, the removal by electrical forces is reduced in time, as aerosols deposit on the filter fibers. We have studied the contribution of this electrical removal and its change in time as a function of aerosol loading. To prove the change in aerosol penetration is due to the reduction of electrical force, the electrical charges were removed from new facepieces by the application of appropriate chemicals. The dust-mist filtering facepieces tested have similar fiber diameters and packing densities, as determined by scanning electron microscopy and pressure drop data. At a face velocity of 10 cm/s (corresponding to 100 L/min through a complete filtering facepiece) and an aerosol size of 0.16 microns, electrical force removal accounts for 69% of the total filtration for the respirator found to have the best filter quality but only 25% for the respirator (from a different manufacturer) found to have the worst filter quality. Our experimental data show that the removal efficiency of these facepieces is reduced in time by as much as this amount. However, under normal wear conditions, the total aerosol particle load is not as high as shown and the filtering facepieces are likely to be discarded before the fiber charges (i.e., the electrostatic attractions) are significantly diminished.
如今使用的大多数过滤式面罩由驻极体材料制成（即过滤纤维上带有大量电荷的材料）。由于这种电去除力的存在，在不增加呼吸器内部气压降的情况下，过滤效率可显著提高；气压降与生理负荷密切相关。然而，随着气溶胶沉积在过滤纤维上，电力去除作用会随时间减弱。我们研究了这种电去除作用的贡献及其随时间的变化，该变化是气溶胶负载量的函数。为证明气溶胶穿透率的变化是由于电力减弱所致，通过施加适当的化学物质去除了新面罩上的电荷。经扫描电子显微镜和气压降数据测定，所测试的防尘雾过滤式面罩具有相似的纤维直径和堆积密度。在面风速为10厘米/秒（相当于通过一个完整过滤式面罩的流量为100升/分钟）且气溶胶粒径为0.16微米的情况下，对于过滤质量最佳的呼吸器，电力去除作用占总过滤量的69%，而对于过滤质量最差的呼吸器（来自不同制造商），这一比例仅为25%。我们的实验数据表明，这些面罩的去除效率会随时间降低多达上述比例。然而，在正常佩戴条件下，总的气溶胶颗粒负载量不像所示的那么高，并且过滤式面罩很可能在纤维电荷（即静电吸引力）显著减弱之前就被丢弃。
