OBJECTIVETo analyze the influence of experimental conditions: Distribution of particulate and the filter condition on the pyrophosphoric acid method for quantitative analysis of free silica in dust.

METHODSAccording to Method for determination of dust in the air of workplace Part 3: Distribution of particulate (GBZ/T 192.3-2007) , Part 4: Content of free silica in dust (GBZ/T 192.4-2007) , the distribution of particulate of 5kinds of dust samples were observed. Different filter conditions were used to determinate the Content of free silica in the 4kinds ofdust samples: 1 filter paper, 2 filter papers, 3 filter papers, 2 filter papers with paper pulp in them.

RESULTSThe distribution of particulate of 4 kinds of dust sampleswere different. The order from high to low is defined with "I, II, III, IV, V" successively. For dust sample I, II, III, the results with different conditions increase successively (P<0.05) . The result in 2 filter papers with paper pulp were not significantly different compared with the reference value (P>0.05) . For dust sample IV, the resultin 1 filter paper were significantlylower thanthe reference value (P<0.05) . For dust sampleV, The results with different kinds of filter type were not significantly different (P>0.05) .

CONCLUSIONdifferent filter conditions should be considered according to thecontent of free silica and the distribution of particulate in dust sample. For the dust sample which has the higher content of free silica and the distribution of particulate, 2 filter papers with paper pulp in themis the better filter condition compared with the traditional way.