Q – How fast do particles of different sizes settle?
A – 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
Q – What is meant by “import dust” and “export dust”?
A – 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.
Q – What is meant by “nett export” dust?
A – 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.
Q – How long is it recommended for the company to carry out the sampling if the levels are constantly in the slight dust category?
A – 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 fall-out 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 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.
Q – How far must the DustWatch unit be placed from the dust source?
A – 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 cline to recommend positions for the units. Each units 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 a way that nett export values can be determined.
Q – What are the options with regards to the Laboratory work and report writing?
A – 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 DustWatch or a site agent subcontracted by DustWatch, 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 DustWatch 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 DustWatch or the company)
Q – How are samples couriered to DustWatch if the company does the bucket changing, but contracts the rest out?
A – Once the buckets have been collected, the contents are transferred to 2-litre bottles. The bottles are then crated and sent to DustWatch 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 an international border. DustWatch then filters the water, weights the samples and writes the reports. When there is enough demand in an area, a site agent will be appointed. 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 DustWatch. A much cheaper solution.
Q – How far do dust particles of different sizes travel?
A – 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.
Q – How do you determine the dust concentration in the monthly reports?
A – 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.
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Dust Monitoring Equipment – Environmental & Hygiene Engineering. Legislation. Dust fallout. Dust watch. Dust monitoring. Dust particles. Occupational health and safety. Hygiene engineering. Environmental engineering