to collect dust passively (i.e. no pump operation) during a sampling
period in the onsite sample and worker preparation area, and (4)
returning the cassette to the sealed shipment bag with the other
air samples. Therefore, the field blanks acted as quality control
against potential contamination during preparation for sampling
and shipment, as well as extended cassette exposure to ambient
field conditions. Two filed blank were taken for the twenty samples
during the study.
4.1.4. Environmental and other variables
Environmental variables, e.g. temperature, humidity, wind
direction and velocity, will affect the dust exposures. In order to
control the environmental variables, an indoor area was designed
as the test area to minimise the effects of wind. The two workers
(with or without DustBubble) started the drilling simultaneously
to make sure they were conducted in the same environmental
situations.
As a quality assurance, the environmental conditions were also
measured using a 5-in-1 weather metre (MODEL: AZ 8910).
Humidity, temperature, wind direction and velocity were recorded
at the beginning, middle and end of each sampling processes. The
results indicated that the environmental variables recorded for the
paired samples were the same, which meant that the environmen-
tal variables need not be considered during the comparison.
During the experimental study, the workers’ comments on the
operation and effectiveness of DustBubbles were also collected to
reflect the workers’ perceived satisfaction towards the use of
DustBubble.