Hello Mr. Potter:

You ask about the most appropriate type of testing. The concept of “testing” especially laboratory testing or “sampling” is a bit misunderstood in the mind of the general population, not least of all because of what I call “The CSI Effect” (1) wherein there is a misplaced belief by the general public that “laboratory tests” represent truth, and can just generally answer questions.

However, that is not the case, and often, sampling and testing actually misleads the recipient of a lab report and directs decision making in the wrong direction.(2) Laboratory results are worthless, except within the context of a set of interpretive rules called “Data Quality Objectives (DQOs);” without DQOs, one doesn’t have data on a laboratory report, one has numbers and units that may be entirely uniterpretable, and are usually useless and untenable, and you could end up looking as looney as Mr. Gerhart.

So when you begin to seek the best testing method, you first have to ensure that you have actually defined your question in a manner that can be answered by “testing,” and then develop a set of DQOs that will answer that question.

In this case, you probably have one of three objectives:

1) Determine the variance (limits) associated with specific activity for numerous batches of granite.

2) Develop an academic database of surface measured activities of randomly selected batches of granite.

3) Determine the contribution of exposure from granite for either your workers or a specific home.

In any case, your data quality objectives will need to address “PARCC” parameters:

Precision:
How reproducible are measurements?

Accuracy:
How close is the value to the true value?

Relevancy:
Do the data speak to the a priori question being asked?

Comparability (Points of reference for decision making process):
This is not needed for an academic database, but is imperative for everything else. Can decisions be based by comparing the results against regulatory or nationally accepted guidelines or at least arbitrary guidelines that are established specific to the case, all before we sampled?

Completeness:
Have the DQOs been met?

These are the foundation of producing tenable data, instead of mumbo-jumbo numbers and useless labreports, and these are the defining character between good defensible data and junk-science. As I have explained elsewhere, (3) it is also the foundation that will permit your data to stand-up in court, if necessary, or withstand scientific rigor.

In your case, you mentioned “exposure,” and that may be putting the cart before the ass, because until you have something against which to compare your “test,” you may only be measuring total exposure, and not be able to make a statement as to what was the contribution of the exposure from the granite. If you want me to address this kind of “testing” in detail, I will do that for you.

Measuring specific activity for batches of granite would not provide any information about exposure. In this type of testing, you would select, from a batch of granitic materials a representative portion that would be submitted to the laboratory. The lab would then prep the materials by ultimately pulverizing the stone. In one of the labs I used to work (Hazen Research), we could easily handle several tons of rock and stone, that would slowly be prepared for analysis – the sample I would eventually receive for analysis would typically be about 300 grams, and it would be representative of say, a five ton sample.

The prep stage goes through a series of stages wherein the sample prep lab ensures that the total mass of material is reduced to a manageable size, whilst ensuring that a representative sample is maintained. Pulverizing the material in imperative since this is how you will reduce sampling error. Then from the final material, samples will be analyzed for a variety of parameters, and most appropriately for your needs would probably include total alpha, beta and gamma. This allows one to confidently speak to the issue of specific activity. By looking at the gamma spec, then we can also speak to the issue of what is decaying.

Developing an academic database is both the easiest, (and least expensive) and also the method which provides the least useful and least tenable information. In developing an academic database, you decide that you don’t really care about exposure, and you don’t really care about confidence in the results (accuracy or precision), and you select any particular type of radiation (alpha, gamma or beta), and you then employ any kind of real-time field instrumentation for that type of radiation. You try to maintain the same reading protocol for each piece of material (raw material or even finished product), and then after thousands of readings, a picture will begin to emerge that will allow you to make certain statements about both composition and intensities (but not a lot else.)

All investigations begin by properly defining the “question.” The question needs to be very specific, and it then is put into the form of an hypothesis; and it is the hypothesis that really gets tested. So begin here by telling me as specific as possible what question are you are really trying to answer, and then on this board, I will walk you through the development of the hypothesis, the establishment of DQOs, and selecting the best “test method.”

Cheers!
Caoimhín P. Connell
Forensic Industrial Hygienist
Forensic Industrial Hygiene

References:
Connell CP, Forensics by Any Other Name, The Monitor, American Society of Safety Engineers, Vol 6, No.2, December 2006

Connell CP, Sample results… What do they really tell us? Presented to the IAQ in Schools and Commercial Buildings seminar, Corpus Christi, Texas, March 2003

Connell CP Sample Results: IAQ Sampling Myths, 13th Annual AIHA/ASSE OEH&S Conference, “Exchanging Knowledge – New Times, New Ideas” Denver, CO October 2007

(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)

AMDG