Twenty personal samples and one bulk samples have been collected
and tested. It was found that the bulk sample contained silica
and 93% of silica existed as quartz. Therefore, only the quartz
was tested during the X-ray analysis.
Twenty respirable samples have been collected and eighteen of
them were valid. They show in Table 2, the results indicated that
none of the measurements exceeded the exposure limits for the
respirable dust concentration (5 mg/m3) and seven samples
exceeded the respirable quartz limit (0.05 mg/m3). Since there
are not more than half of respirable quartz concentration values
(samples) that were below LOD, the non-detectable values were
replaced as follows: LOD=ð
ffiffiffi 2
p
volumeÞ (since the GSD were less
than 3).
The hypothesis of normal distribution could not be rejected for
logarithmically transformed respirable dust (p = 0.745 > 0.05) and
respirable quartz (p = 0.236 > 0.05) concentration values (Kolmogorov–
Smirnov test), so the GM is a better way to describe
the central tendency of lognormal distributions.