Questions and Answers (Click the
Questions to read the Answers)
- How
fast do particles of different sizes settle?
- The speed at which particles
settle depend on many variables. The following page will
allow you to determine settling velocities for different sized
particles. Click
here
- What
is meant by "import dust" and "export dust"?
- Import dust is the term used
to describe dust coming from a source other than the main
source being monitored by DustWatch.
Export dust is dust that is coming from the main source being
monitored. It does not matter where the dust is going
the important thing is that the dust is being exported from
the main source.
- What
is meant by "nett export" dust?
- Nett export dust is the term
used when two DustWatch units are used on opposite sides of a
dust source. The import dust from the one unit is
subtracted from the export dust from the unit on the opposite
side. This ideally provides a nett export.
We say ideally because there are other factors that influence
this, such as heat generation over a dust source, water in the
area of the DustWatch and incorrect positioning of the
DustWatch units, either too far or too close to the dust
source.
- How
long is it recommended for the company to carry out the sampling if
the levels are constantly in the slight dust category?
- Following international and
South African trends, we recommend dropping the frequency of
sampling to one sample every quarter. Sample for one
month in the middle of each of the four seasons.
This will continue the sine curve trend data so that the
company will be able to have an up to date history of their
fallout data. So long as the results remain in the
slight dust category, we don't see how any inspection
authority could have a problem with this.
It would even be reasonable to only sample in the dry season,
but from our experience we have found that to have a yearly
trend going back a number of years is very valuable.
- How
far must the DustWatch unit be placed from the dust source?
- From our experience if the
unit is positioned too close to the source then the unit will
get inundated with dust and all the buckets will be
loaded.
As an example the unit should not be positioned within 100
meters of a dusty road.
Much depends on what the client requires from the DustWatch,
and in most cases we are asked by the client to recommend
positions for the units. Each unit's position should be
considered taking both the dust source and the potential
problem areas, such as towns, farms, and other mines.
When using more than one DustWatch, all the units should be
positioned in such away that nett export values can be
determined.
- What
are the options with regards to the Laboratory work and report
writing?
- In short the process of
Fall-out monitoring is as follows, the mine can choose at what
stage they would like to contract the work out.
- Purchase DustWatch
units (required)
- Install DustWatch
units (required)
- Prepare and
change buckets every 2 weeks. (Optional, Could be
contracted out, either to GKEHE or a site agent
subcontracted by GKEHE, or the company could do it
themselves.)
- Filter the
contents of the buckets on to filters using standard Lab
methods. (Optional, the company could do it or they
could contract it out.)
- Weigh the filters
containing the dust. (Optional, normally done by GKEHE or
by the company)
- Use our excel spreadsheet
or make your own, for doing some simple
calculations. Draw up tables and trends and write a
short report every month. (Optional, usually done by GKEHE
or the company)
- How
are samples couriered to GKEHE if the company does the bucket changing,
but contracts the rest out?
- Once the buckets have been
collected, the contents are transferred to 2-litre
bottles. The bottles are then crated and sent to GKEHE
using the company's preferred courier. The bottles take
up less space than the buckets and are less likely to leak
during transportation.
We receive bottles from Botswana, sent to South Africa across
and international border. GKEHE then filters the water,
weighs the samples and writes the reports.
When there is enough demand in an area, a site agent will be
appointed, and the site agent will be able to do the bucket
changing and the filtering of the buckets. Leaving only
the dried filters in petri dishes to courier to GKEHE. A
much cheaper solution.
- How far do dust
particles of different sizes travel?
- There are many factors that
influence the distance traveled by particles.
Our diagram
showing how vegetation affects fall-out dust also gives a good
indication of the different particle sizes and how wind is
able to blow them around.
- How
do you determine the dust concentration in the monthly reports?
- The open area of the buckets
used to catch the dust is 0.0254 m2 and the time
period is usually 14 days, depending on when the buckets are
changed.
The dust that collects in the water in the bucket over the 14
day period is filtered through 8 micron filter paper.
The filter paper then weighed to determine the mass of dust
collected in the bucket.
The mass of dust is divided by the number of days, and then
divided by the area of the bucket to yield a result in units,
mg/m2/day.
Click
here to see an example of the tables being referred to.
www.safetyhealthtraining.com
is a site that sells induction training material.
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