4. Experimental methods
The main research methods taken during this experimental
study were NIOSH 0600 and 7500 methods. Following these meth-
ods, personal respirable samples were collected and analysed to
determine the respirable dust and silica dust exposure of workers
during the process of concrete drilling.
4.1. Sampling methods
4.1.1. Personal respirable samples
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 recom-
mended flow rate of 1.7 l/min using an airflow calibrator. The sam-
pling 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-selec-
tive particulate collector recommended by NIOSH (1998a,b).
The duration of samples were 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 de-
tect 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=m 3
; flow rate : 1:7 l=minÞ