Conscientious particle counting

Research was undertaken to test whether different particle counters yield t he same particle count and size distribution information, to assess the pos sibility of using particle concentration standards from other applications in the water industry, and to develop and test a concentration standard for use in the water industry. Five particle counters were used, including dup licates of each of two manufacturers' light-obscuration instruments (common ly used in the water industry) and one electrical sensing zone (ESZ) instru ment. On all types of samples (latex spheres, a commercially available line test dust used as a standard in other industries, and water treatment plan t samples), the light-obscuration instruments consistently measured far few er particles in the smallest sizes (2-5 mu m) than the ESZ instrument, and evidence is presented that suggests the ESZ instrument is more correct. Rec ommendations for standards to use with light-obscuration instruments includ e using a multimodal count standard using latex spheres of two sizes, with those sizes being in the middle of standardized size ranges; using separate sizing standards at the boundaries of the size ranges; and avoiding any us e of particle counters for regulatory purposes at this time.