|
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.
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.
There are over 2500 different products ranging
from paints textured coatings through floor
tiles and flooring systems to sanitary ware
and roofing materials. Where there was a need
for a long lasting material which can deaden
sound in or insulate an area or used as a
binder in a material asbestos was a good
choice up until legislation prohibited the
use.
-
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 sampling and fibre counting of samples
to ISO 17025.
This method is the HSE’s approved
method of determining the number of fibres
in the ambient air and can be applied to
the new :-Determination of airborne fibre
number concentrations: A recommended
method, by phase-contrast optical
microscopy (membrane filter method) World
Health Organisation 1997 ISBN 92 4154496 1
-
Compliance Sampling - to asses
whether workers are in compliance with
the four hour and 10 minute control
levels specified in the CAR
-
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 removal work 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
-
Reassurance Sampling – This is
monitoring which is conducted in
certain circumstances to confirm
that residual fibre concentrations
are <0.01f/cc.
-
4-Stage
Clearance
Certificate of
Reoccupation –
Independent
testing to
ensure that the
area is suitable
for future use.
This is a
legislated
necessity to
ensure that
anyone entering
an area where
asbestos
containing
materials have
been worked on
or removed is
kept safe
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.
|
