LCS Laboratory Inc., offers laboratory services to Health and Safety professionals around the globe. We also offer training of field personnel, and we are always happy to answer your professional  questions. Feel free to leave your comments below this article.   Today’s topic is: “What is the Difference Between Different Types of Blank Samples?”

In Air Quality Testing, consultants rely on laboratories to provide good quality sampling media  such as filter cassettes, adsorbent tubes,  IOM samplers and so on. On another hand, the laboratory relies on the client and proper shipping so as samples arrive safely without being contaminated in transit.  The only way to confirm the quality of the sampling media, in shipping, and field handling is to test a BLANK SAMPLE.

For the sake of this discussion, we will be using an air sampling cassette as an example of the sampling media (the same applies to any media used in air testing).

A BLANK SAMPLE or Blank Cassette is a cassette, from the same batch that were used on a project. What makes it different from the rest, is that it was never used to collect the sample, it is used as a control. There are number of different type of blank samples.

Field Blank Sample

This is the best quality blank sample. The next paragraph explains how it should be taken.

You receive the cassettes from our laboratory, you check them while you are in the office, and you bring them to your client’s workplace. After you start air sampling, you take several unused cassettes, you open them and close them as if they would be used for sampling.  Those cassettes are your FIELD BLANKS. Please label them with a marker and write down their information on a request form. Return the field blanks with the rest of your samples to our laboratory for analysis.  We analyze the samples and the blanks and report our findings back to you.  This is when you need to check what the reading is on the blanks. You may have different situations.

  • Laboratory results for Blank Sample(s) are below the Reporting Limit. This is the best outcome. No contamination was detected on the blank cassettes and results are reliable.
  • Laboratory results for Blank Sample(s) are readable but only slightly above the method sensitivity. This does not affect quality of the results, but indicates to you that there is minor contamination in ALL samples  with a chemical either on field or during transportation.
  • Laboratory results for Blank Sample(s) are high and comparable with the results found on actual samples. The results are unreliable and likely overestimate the true concentration of chemicals in the air.  All your samples were contaminated on one of the stages: shipping to you-> trip to your client-> cassette handling (the most common cause) -> return shipping to our laboratory.

Travel Blank Sample

This is a widely used technique, but it does not tell you the full picture.

You receive the blank cassettes from our laboratory, you take them to your client and back, but you actually never open them or even take them out of the case.  If we detect any contamination on them, this indicates contamination during the shipping. But you would not know about contamination which may occur during handling.

Laboratory Blank Sample

This kind of blank is added by a laboratory and analyzed with your field samples.

This is done to show your client that you actually care about having blank samples, but may have run out of spare cassettes, and could not provide a field blank.

LCS Laboratory Inc., is here to help you to build a dependable air sampling procedure for you and your clients.   Please email us to discuss your project. To learn about how many blank samples you will need to take, please check our article. To learn more about Industrial Hygiene techniques and our services, please check our IH page.

 

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