The test dust used in the NFPA recommended standard for the contaminant sensitivity must be obtained by classifying ACFTD, which is stated as the standard material, into the defined particle size ranges.
This report describes the method and results of classification with test dusts ACFTD, JIS 3rd: Silica dust and JIS 8th: Kanto Loam dust into particle ranges of 0-5, 0-10, .....0-80 micrometer.
Particle diameter distribution of the test dusts classified in this study and classified dust sent from the Oklahoma State University (OSU) are analyzed and compared. With the dust from OSU, the particle frequency decreases near the upper boundaries of the higher particle size ranges (greater than 0-40μm range), hence the discrimination between the classified dusts of 0-50μm range and 0-80μm range is difficult.
It was recognized that the description of t he particle classification in the NFPA recommended standard should be revised to yield stricter definition.

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Pump contaminant sensitivity tests were performed using the test facility described in the rust report and the classified test dust described in the second report.
Three types of pumps, namely vane, gear and piston pumps, were used as test pumps. The following results were obtained through experimental verification of the test method using the above mentioned pumps;
(1) The repeatabilityo f the NFPAr ecommendedst andardc an be approved in its presents tate; however, it could be improved.
(2) The reproducibility of the test results at different laboratories is not satisfactory. A more strict definition on the particle distribution of the test dust shall be suggested to obtain better reproducibility. The item defining ability o f filter circuit, or in other words, the time for filtration, should be added to the standard.

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