|
Asbestos is a naturally forming mineral,
which has been commercially mined
for its useful properties of heat resistance,
chemical inertness, low thermal conductivity,
flexibility and high tensile strength.
There are three main types of asbestos
used commercially in significant
quantities:
Chrysotile (white asbestos) Amosite
(brown Asbestos) and Crocidolite (blue asbestos).
It is estimated that over 5 million
tonnes
of asbestos was imported into the
UK from countries such as Canada and South
Africa.
| Where is
Asbestos it Found? |
Asbestos was manufactured in many forms
with the most common including thermal
insulation for pipe work, insulation
board for boxing and panelling and
cement sheeting for roofing. Given that asbestos
fibre acts as an excellent bonding
agent,
asbestos fibre may also be found
in many materials that in the past have been
utilised in the construction industry.
-
Chrysotile is commonly associated
with cement products and given its softness
and strength was also often woven into
rope used in sash windows and heat seals.
-
Amosite is most often associated
with insulation board and pipe lagging.
-
Crocidolite is widely considered
to be the most hazardous of all of the
asbestos minerals and was commonly used
in spray materials and pipe lagging.
Fibre Counting:
REC Asbestos Limited is UKAS accredited
for asbestos sampling and asbestos fibre counting of samples
to MDHS 39/4: November 1995, Membrane
Filter Method using Phase Contrast Microscopy.
This method is the HSE’s approved
method of determining the number of fibres
in the ambient air and can be applied to
-
Compliance Sampling - to asses
whether workers are in compliance with
the four hour, 10 minute and 12 week action
levels specified in CAWR
-
Background Sampling – Conducted
to establish background fibre levels prior
to any activity that may lead to airborne
asbestos contamination.
-
Leak (enclosure check) Sampling – This
is performed outside the enclosure while
asbestos is being removal work is in progress
and is in progress to check that the environmental
control systems are adequate.
|
-
Assessment of the
Suitability of respirator protection -
This is monitoring inside the enclosure
while asbestos removal is in progress and
is conducted to assess the effectiveness
of the dust suppression measures and the
suitability of respiratory protection
-
Clearance Indicator Sampling – This
is monitoring in a cleaned and visually
examined enclosure from which asbestos
has been removed or encapsulated.
-
Reassurance Sampling – This is
monitoring which may be conducted in
certain circumstances (such as when the
enclosure has been removed) to confirm
that the residual fibre concentrations
are <0.01f/ml.
Principle of the
method:
A measured volume of air is drawn through
a membrane filter, which is subsequently
mounted on a microscope slide and rendered
transparent. Fibres on a measured area
of filter are counted using Phase contrast
microscopy and the number concentration
of fibres is calculated.
|
