EBT Calibration: The most misunderstood term in breath alcohol testing

EBT Calibration: The most misunderstood term in breath alcohol testing

One of the most important responsibilities of a Breath Alcohol Technician (BAT) is to ensure that the Evidential Breath Tester (EBT) they use gives accurate results that can be relied upon.  Every student that we train as a BAT receives training in how to check and document that the EBT gives correct readings.  What’s the name of that procedure that checks the accuracy of an EBT?

If you answered “Calibration,” you are wrong.  The correct answer is any one of the following terms: Accuracy Check, Calibration Check, External Calibration Check, or Calibration Verification, to name some of the most commonly used terms.  The terminology used to describe the procedures to maintaining an EBT in accurate condition can be confusing, so we start every discussion on this topic by untangling the confusing terminology.

First of all, there are two distinct procedures necessary to maintain an EBT in accurate condition. One procedure is called “Calibration.”  The term DOT uses in CFR Part 40 to describe the second procedure is “External Calibration Check.”  That fact that the word “calibration” appears in both procedures causes people to confuse one term for the other.  In order to minimize this confusion, we’ll use the term “Accuracy Check” to refer to what DOT calls “External Calibration Check.”

You may think to yourself, “But isn’t Calibration the same thing as an Accuracy Check? “  It’s not unheard of for personnel to use the term “Calibration” as a catch-all word to refer to both procedures.  If you use “Calibration” as a catch-all term for both procedures, you’ve got some un-learning to do.  The Calibration procedure is not the same as the Accuracy Check Procedure.

Calibration and Accuracy Check explained

So what’s the difference between Calibration and Accuracy Check?  The Calibration procedure makes an adjustment to the instrument to make it read more accurately.  When doing training we will frequently use the term “Calibration Adjustment” to emphasize this point.  We use the example of adjusting an older model bathroom scale as an example of a Calibration Adjustment.  The old model analog bathroom scale has a needle pointer or a dial that moves when you step on the scale to show your weight.  The process of turning a knob on the scale to make the scale read higher or lower is a Calibration Adjustment.

The Accuracy Check procedure, on the other hand, documents how accurately an instrument is reading.  The Accuracy Check procedure does not make any adjustment to the device; it simply documents whether the device is giving results within the acceptable range of accuracy.  Back to our example of a bathroom scale: we can perform an Accuracy Check on our scale by placing a known weight – say a 25 pound bag of dog food – on the scale and observing the reading on the scale.  We haven’t changed anything about how the scale reads, but we now know if the scale is reading high, low, or right on the money.

To check the accuracy of an EBT, instead of a weight we use what’s called an “ethanol standard,” which is an ethanol gas with a known ethanol concentration.   There are two types of ethanol standards:  compressed ethanol gas tanks, and wet bath simulators.  Compressed ethanol gas tanks are the most widely used because of its portability and ease of use.  The ethanol concentration of each ethanol gas tank is printed on the label of the tank; for DOT testing typical ethanol concentrations are .038 or .040 BrAC.  When performing an Accuracy Check, we use the EBT to test the ethanol gas, and compare the reading on the EBT to the known concentration of ethanol gas.  We now know if the EBT is reading high, low, or exactly correct.  (See Ethanol Gas Calibration Standards for Breath Alcohol Testing Devices: Making the Complex Easier, DATIA Focus, Winter 2016, Vol 9 Issue 1, for a detailed discussion of ethanol gas standards.)

Which is more important:  Calibration Adjustment or Accuracy Check?

It may be counter intuitive, but in terms of choosing which procedure best supports the defensibility of an alcohol test result, we make the argument that the Accuracy Check procedure has more importance than the Calibration Adjustment procedure.  Here’s our reasoning:  DOT regulation 40.267(c)(5) states that if an EBT fails an accuracy check immediately after a positive confirmation test result (.020 or greater), then every test performed on that EBT since the last valid Accuracy Check is cancelled.  In other words, a successful Accuracy Check procedure validates a confirmation test result, and a failed Accuracy Check Procedure invalidates the confirmation test.

That is why BATs are trained to perform an Accuracy Check as soon as possible after a positive confirmation test, before dismissing the employee.  If the EBT fails the Accuracy Check, the BAT has the opportunity to calibrate the device, perform another Accuracy Check, and re-test the employee to obtain a successful test result.

Conclusion: Accuracy Checks document a quality breath testing program

Understanding the basic concepts of Calibration and Accuracy Checks, and getting the terminology right, is essential to ensuring the quality of a breath alcohol testing program.  And that’s what an Accuracy Check does:  it documents that an EBT gives results that can be relied upon. There is no better way to demonstrate the quality of a breath testing program than a properly completed logbook that lists every Accuracy Check result, and that shows the device gives consistently accurate readings.