Personal respirable dust samples were collected using pumps
(GilAir-3) connected to 10 mm nylon cyclones, as shown in
Fig. 2. Each set of sampling equipment was calibrated to a recommended
flow rate of 1.7 l/min using an airflow calibrator. The sampling
medium was a 37 mm, 5.0 lm pore size PVC filter, supported
with backup pad in a two-piece cassette filter holder. This 10 mm
nylon cyclone with its attachments was a light weight, size-selective
particulate collector recommended by NIOSH (1998a,b).
The duration of sampleswere determined by the limit of detection
(LOD) parameters of laboratory analysis and the actual operational
time of each work process/trade. From LOD perspective, the duration
of samples should be longer enough for the laboratory analysis to detect
the presence of silica, which gives the duration a lower duration
limit (LDL). The LDL could be calculated by the following equation:
LDL ¼ LOD=RELðNIOSHÞ=flow rate ¼ 118 min
ðLOD : 0:01 mg; REL ðRecommended exposure limitÞ by NIOSH
: 0:05 mg=m3; flow rate : 1:7 l=minÞ
Therefore, the duration of samples should be more than
118 min. In order to reduce the variability and narrow the confident
limit, all the respirable samples during the study were taken
for approximately 180 min. During the experimental study, trials
of the block-drilling controls were conducted in two rounds consisting
of 10 trials in each round. Total 20 samples have been collected
with ten samples for each situation: with and without
DustBubble. In addition to the personal respirable samples, other
related variables were also collected and recorded, including filed
blanks, and environmental variables.