Laboratory analysis
Two different analysis methods were used for personal samples
and bulk samples. All analyses were conducted at the laboratory of
Hong Kong Polytechnic University. The LOD and LOQ (limit of
quantification) were 0.01 mg and 0.03 mg respectively.
4.2.1. Personal samples
All personal samples were firstly analysed for total weights
according to NIOSH 0600 method using Mettler-Toledo XP 26 balance,
which gave the concentration of total respirable dust. The
samples were then analysed by X-ray following NIOSH 7500
method.
4.2.2. Bulk samples
A quick qualitative analysis on the bulk samples using X-ray in
accordance with NIOSH 7500 method was conducted to determine
the presence of silica and the relative levels of the three silica
forms. If the presence of silica was confirmed and the major percentage
of silica is quartz, the personal respirable samples collected
during this experimental study were only analysed for
quartz.
4.3. Testing materials and tools
Significant basis of this experimental study was the fact that all
samples should be carried out under comparable conditions. In order
to obtain reproducible results to compare drilling process with
or without Dust Bubble, only a study in a test room was taken into
consideration. With measurements taken at a real-life workplace,
environmental impacts like air change rates, teat area sizes or
changes in material mixtures can seldom be eliminated sufficiently.
However, conditions of the experimental study should be
set up as close as possible to those in practice. Therefore, all the
materials used were kept the same as the practice.
It was estimated that it would take around 1 min for 1 hole