ABSTRACT
Asbestos has been extensively used to insulate boilers and associated heated pipe work
throughout the world. Managing human health risks posed by asbestos during the
removal of lagging poses many challenges. For this reason, acquiring a better
understanding of factors that lead work tasks to produce high airborne fibre
concentrations is important for the development of improved control methods.
Aim: The aim of this study was to link observed work tasks and work practices with
measured airborne concentrations of fibres in order to identify those factors contributing
to high airborne concentrations generated during boiler de-lagging. The investigation was
based on a study of two employees working on a boiler de-lagging contract lasting
twenty-one days and resulting in a total of 79 measurements of airborne asbestos fibres.
The primary form of asbestos dust control for the duration of the contract was the
application of non-amended water.
Objectives: To definitively identify the presence and type of asbestos lagging as well as
quantify airborne fibre concentrations for two work tasks i.e. Stripping (removing
lagging) and Bagging (placing removed lagging into bags as well as cleaning spills), in
order to demonstrate how they may influence airborne fibre concentrations.
Methodology: The type of asbestos was confirmed by Scanning Electron Microscopy.
Phase Contrast Microscopy (PCM) was selected as the primary measure of airborne
asbestos fibres. A Work Practice Checklist was developed to link observed daily Work
Tasks and Work Practices with the concurrent airborne fibre concentrations. The
geometric mean was a useful measure of central tendency for the data since it was highly
skewed to the right (positively skewed). However, for public health purposes the
arithmetic mean was also considered because it provides some idea of health risk where
the human respiratory system is assumed to accumulate fibres linearly with
concentration.
Results: Bulk sample analysis confirmed the presence of both chrysotile and amosite
asbestos lagging. Work Practices such as Wetting, Stripping and Bagging asbestos, were
undertaken in a relatively uncontrolled manner during the first three days of the project
resulting in mean airborne fibre concentrations of 1.171 f/ml for the Stripper, ranging
from 0.612 to 1.236 f/ml and 0.315 f/ml for the Bagger, ranging from 0.107 to 0.631f/ml.
These means were 4.5 times and 2.3 times respectively, greater than the means calculated
for the entire project. The overall mean fibre concentration was approximately five times
greater for personal samples, 0.198 f/ml (± 1.647) than for the concurrent static samples,
0.039 f/ml (± 0.129).
The analysis of log transformed data revealed several strong tendencies for airborne fibre
concentrations when related to Work Tasks and Work Practices. The difference between
stripping asbestos in small manageable as opposed to larger unmanageable pieces was
highly significant (p < 0.001). Smaller manageable pieces resulted in much lowerconcentrations. The manner with which asbestos was bagged was also highly significant
(p < 0.001). Bagging in an uncontrolled manner resulted in much higher airborne
concentrations. Surprisingly, the degree of wetting was not as important as expected:
working dry did not generate significantly more fibres than working with saturated
insulation but did generate significantly more fibres (p < 0.005) than working with
partially wet insulation (which lead to the highest concentrations). A limitation to
interpreting the Wetting work practice was the low number of samples taken within the
dry category (n = 5).
The difference in mean sample concentrations between personal and static samples for
this study demonstrates the importance of spatial and temporal proximity as a
determinant for airborne fibre concentrations. It also showed clear associations between
what can be described as rushed, reckless Work Practices, and the resulting high levels of
airborne fibre concentrations (exceeding the OEL). Within the context of this project,
these findings demonstrate the utmost importance of providing the appropriate training
and supervision of employees, not only for protecting themselves against airborne
asbestos fibres, but for removing asbestos in manner that results in the generation of the
least amount of airborne fibres possible
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/6063 |
| Date | 11 February 2009 |
| Creators | Randolph, Robert Winston |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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