Isokinetic sampling is very tedious and we, as people who try to serve our clients best interests are looking for ways to minimise costs, and in doing this we are having a serious look at the benefits of doing isokinetic sampling.
Questions we ask
Is it worth the expense?
What useful information is obtained?
Is there not an easier way to get similar information?
These comments are based on the South African Industry, and experience is predominantly on mines falling under the Department of Minerals and Energy, Mine Health and Safety Act.
The British Standard Test method for Isokinetic sampling is BS 3405. This standard is unfortunately only available to be purchased and cannot be published on a web site.
Isokinetic sampling for some reason seems to have become over complicated and technical.
The main question to answer is : What are the reasons for taking "Isokinetic samples"?
As mentioned already it is usually done to calibrate instrumentation or just to determine the dust load in a stack.
From our experience the latter is less common, and almost always isokinetic sampling is required when the load in the stack or duct is very low, i.e. when the instrument is reading at the bottom of its range, or the dust plant is working well.
Any mine needs to weigh up the costs versus the benefits of isokinetic sampling. Very often the benefit side of the scale is a bit on the light side.
The main difficulty with isokinetic sampling is to try and make the sample as representative as possible of the dust in the stack or duct, without excessive costs.
The arguments are that the perimeter of the sampling tube will effect the air flow quite drastically in and around the tube unless the flow is very similar past the outside and into the tube.
The above problem is very significant if the area of the perimeter is similar to that of the area of the sample.
However if the sample area, i.e. the diameter of the tube is larger, then the disturbance caused by the perimeter is less significant because more dust is collected.