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 (Kol-
mogorov–Smirnov test), so the GM is a better way to describe
the central tendency of lognormal distributions.
A non-parametric statistical comparison (Wilcoxon Test) was
conducted to investigate whether there were significant differ-
ences between the respirable dust and respirable quartz dust con-
centrations of operators with DustBubble and without DustBubble.
The results showed that there were significant differences between
the exposure levels to total respirable dust (p = 0.025 < 0.05). The
workers using DustBubble exposed to low level of respirable dust,
which meant the use of DustBubble could reduce the respirable
concentrations by 63% (GM: from 0.27 mg/m
3
to 0.10 mg/m
3
; esti-
mated reduction = (1 0.09/0.29) 100% = 63%).
For respirable quartz dust, the estimated reduction of respirable
quartz by DustBubble is 43% ((1 0.04/0.07) 100%). However, the
results of statistical comparison indicated that there were no signif-
icant differences between the exposure levels to total respirable
quartz dust (p = 0.144 > 0.05), which suggested that the use of Dust-
Bubble could not significantly reduce the quartz exposure level of
workers when drilling concrete. Moreover, both the GM of quartz
concentration values of two groups (0.07 mg/m
3
and 0.04 mg/m
3
respectively) were over or close to the exposure limit, which sug-
gested the concrete drilling process can generate high level of
quartz dust and DustBubble is inadequate to protect workers. Other
dust control measures (e.g. wet methods, and LEV) should be taken
to reduce the quartz exposure level to below the limit. The workers
should also wear appropriate respirators.
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 (Kol-
mogorov–Smirnov test), so the GM is a better way to describe
the central tendency of lognormal distributions.
A non-parametric statistical comparison (Wilcoxon Test) was
conducted to investigate whether there were significant differ-
ences between the respirable dust and respirable quartz dust con-
centrations of operators with DustBubble and without DustBubble.
The results showed that there were significant differences between
the exposure levels to total respirable dust (p = 0.025 < 0.05). The
workers using DustBubble exposed to low level of respirable dust,
which meant the use of DustBubble could reduce the respirable
concentrations by 63% (GM: from 0.27 mg/m
3
to 0.10 mg/m
3
; esti-
mated reduction = (1 0.09/0.29) 100% = 63%).
For respirable quartz dust, the estimated reduction of respirable
quartz by DustBubble is 43% ((1 0.04/0.07) 100%). However, the
results of statistical comparison indicated that there were no signif-
icant differences between the exposure levels to total respirable
quartz dust (p = 0.144 > 0.05), which suggested that the use of Dust-
Bubble could not significantly reduce the quartz exposure level of
workers when drilling concrete. Moreover, both the GM of quartz
concentration values of two groups (0.07 mg/m
3
and 0.04 mg/m
3
respectively) were over or close to the exposure limit, which sug-
gested the concrete drilling process can generate high level of
quartz dust and DustBubble is inadequate to protect workers. Other
dust control measures (e.g. wet methods, and LEV) should be taken
to reduce the quartz exposure level to below the limit. The workers
should also wear appropriate respirators.
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