A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
subsequent water leakage during operation, retightening the bolts is
carried out some time latter after initial tightening.
15. After the construction of watermain, prior to hydrostatic pressure
test, swabbing is carried out. What is the purpose of swabbing?
(DW7)
Pipelines should be tested before commissioning to check the strength of
watermain and the absence of leak. Before carrying out hydrostatic
pressure test, swabbing is conducted to clear out rubbish and dirt left
inside the pipeline during construction. Swabbing is required for pipes less
than 600mm diameter because for larger size of pipes, they can be
inspected internally to ensure cleanliness.
After carrying out of hydrostatic pressure test, test for water sterilization is
then conducted which involves collecting water sample from the pipeline.
The purpose is to check the water quality like colour, turbidity, odor, pH
value, conductivity etc. and is compared with the quality of water drawn
from water supply point.
16. What are the controversial health issues of using asbestos
cement pipes for watermain? (P2)
There are suspected health hazard for using asbestos cement pipes for
watermain. In drinking water the gastrointestinal tract cancer risk depends
on the amount of asbestos swallowed. When asbestos cement pipes are in
good condition, there should be little safety problem. However, when the
pipes become aged so that some may break down, it then become a great
hazard. When someone takes a little asbestos which are distributed to
other parts of the body so that no single parts of the body have excessive
amount of asbestos, the risk should be theoretically on the low side. The
harmful effect of asbestos is its ability to accumulate in human body. The
microscopic fibers lodged in tissues can act like time bombs and cause
cancer years later. Since asbestos exposure is cumulative, adults have
three or four decades to develop cancer after exposure while youngsters
have six or seven.
However, according to the findings of WHO, asbestos fibres are too large
to be absorbed during the digestion. Therefore, the chance of significant
transmission of asbestos fibres would seem to be low. Some evidence
suggests that high density asbestos-cement products pose no detectable
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