Troubleshooting Projects - The Art of Isokinetic Sampling
Dr Roger S Brown, Oakwood Environmental Services, Feltham, Middlesex. Tel: 07799 623891
Earlier this year I wrote an article on how to sample for gases and as promised I am writing again but this time the focus is on Isokinetic Particulate Sampling.
Over the years I have conducted, commissioned, run training courses and audited Source Emission testing in many countries working with local and foreign teams. It is true to say that the poorest particulate testing I have experienced has been here in the UK mainly due to lack of understanding and lack of time allowed for valid tests to be undertaken and lack of charging a true commercial rate for the work.
I don’t plan to reiterate all the points I made in the earlier article but planning and discussion with clients and regulators is essential in obtaining the correct sampling methods and obtaining the desired result for the client.
The measurement of particulates is often seen as a routine sampling requirement, but it is a complex procedure and needs careful thought as to what the objective is. Whether it is compliance, research or product development, all will require different applications of the Standards.
Standards to be Followed
There are differences in the philosophical approach to particulate sampling in the EU/UK and in the USA and this can lead to issues.
In the USA a particulate method and the conditions they are sampled by are essentially defi ned by the Federal Register as a “proscriptive document” defi ning the procedure in detail. Legislation is effectively enacted against this method and the levels of particulate that are determined by it. What is key is that the method is followed to determine a known result. The requirements for uncertainty budgets are hence not inherently required as everyone will essentially use the same equipment, same method and same procedures; and the fi eld is hence levelled. However, remember this may not be the actual level of particulates emitted but the levels emitted under a defi ned set of conditions and specifi c temperatures, and these can be different in the stack to that which are emitted.
In Europe and the UK, we have allowed a range of equipment to be used and provided the method conforms to the specifi cation in BS EN13284-1 or EN 9096 and the performance criteria are met, then the samples are valid. However, this then leads to variations and obviously now the uncertainty of the measurements becomes more important. Regulators now must compare results obtained by differing pieces of equipment applied in very slightly different ways.
Remember the results obtained by following one method do not necessarily equate to the same answer using a different method because the nature of the particulates will vary with the temperature the fi lter is held at. Is the fi lter in stack and hence at stack temperature or external (out of stack fi ltration) and at the fi lter box temperature (120o
C, 160o C or 180o C)?
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