sampling of dust of an airborne nature is not only the internationally
acceptable method of determining dust concentrations but is in general
use in South Africa.
While the Department of
labour advocates the sampling method, they do not have their own
sampling guidelines or established method and use that devised by the
Department of Minerals and Energy whenever dust of an ore or coal is
As an alternative the NIOSH
guidelines are used.
The method and procedure
outlined below thus relates directly to the guidelines for gravimetric
sampling published under the auspices of the Department of Minerals and
Energy – GUIDELINES FOR THE COMPILATION OF A MANDATORY CODE OF
PRACTICE – No. 1 PERSONAL EXPOSURE TO AIRBORNE POLLUTANTS.
and Measurement Criteria Used
sampling is undertaken using sampling pumps having the Government Mining
Engineer Approval certificate GO8 together with one of two standard
on the requirement for either total dust or respirable
dust monitoring or both, the sampling train will differ as follows:
respirable dust constitutes dust of a particle size below about 7,0µm
an approved make fixed duty separating cyclone is used in circuit to
separate particulate of a size greater than 7,0µm.
particulate is collected in a grit pot below the cyclone and can be
discarded or retained for bulk sample purposes.
The cyclone design permits peak efficiency at the pump setting of
1,9 litres/second, a rate which closely equates the metabolic breathing
rate of a normal healthy adult human being.
Should the rate vary by more than 5% at the conclusion, the
sample is discarded.
dust constitutes all dust that can be collected as an airborne
particulate and as no respirable dust has to be separated, an impinger
section replaces the cyclone to allow a uniform distribution of dust on
the capture media filter. Calibration is undertaken in the same way as outlined above.
is undertaken before and after each sample.
Filter Media for use in the
advocated filter used for the sampling is the cellulose filter media
approved in terms of the same guidelines outlined.
weighing of filters is undertaken in our own laboratory using weighing
equipment, a digital
micro-balance capable of reading to the nearest 10 micrograms in terms
of the guidelines, with our balance reading to 0,1 microgram.
the weighing, determinations are made to correct the filter for moisture
content by permitting it to stabilise in a compartment together with
reference filters, which are always kept in the laboratory clean room. The minimum stabilisation period is 12 hours.
analyst wears laundered cover clothing including gloves, mask and hair
cap in non-static materials. The
analyst is tethered using a static line to the clean room earth
mass determinations are undertaken using statistical averages of masses. Our facilities are constantly inspected by the Department
Inspectorate, approved and accredited, and a periodic cross-laboratory
assessment is undertaken with other laboratories.
following things are considered on site
Positioning of Filters
trains are located on personnel as required by the code of practice.
trains are secured at a height consistent with the normal breathing zone
of an adult worker.
our assessment procedure differs from the guidelines, is the assessment
of working areas where the duration of the operation does not equate an
8 hour shift.
such conditions we move the sampling train from time to time, remaining
well within the positions normally taken by operators to achieve a more
balanced and representative result as long as the operation occurs.
are time weighted to an eight hour shift.
Respirable or Total Dust?
we suspect the existence of a toxic dust with a Threshold Limit Value
(TLV) in respect of respirable dust we sample for respirables.
we consider that there is a necessity to establish a total spectrum, we
sample for both. Normally
we only sample for total dust for dust-control
analysis of dust filters can be undertaken to establish the elemental
composition of the collected samples.
To achieve this as a representative sample we combine various
filters from an area into one composite sample for analysis.
on the requirements of the original specification, or Act/guideline the
compliance can be accurately determined.
specifications call for a nominal “no visible dust requirement”,
which becomes a very subjective requirement as not even the
internationally accepted standards call for “no dust”.
stipulation is further complicated by the presence of dust in any
building, plant or even offices, as only the best of clean rooms are
totally devoid of particulate. To
then assess which of the dust measured has resulted from the operation
is an impossibility.
– Threshold Limit Value
– Time Weighted Average
– Particles not otherwise classified