FOCUS ON ALCOHOL TESTING BY JACK SINGLETON, PRESIDENT, ALCOPRO, INC.
Ethanol Gas Calibration Standards for Breath Alcohol Testing Devices: Making the Complex Easier
O
ne of the first questions asked when disputing a positive breath alcohol test is, “How do you know the
breath alcohol testing device was reading accurately?” Te answer should be easy: “Here’s a copy of the calibration log for the instrument that shows all the accuracy checks and calibration adjustments performed on this instrument, including the accuracy check done right aſter the positive test in question.” In addition to the operator’s diligence
in performing and documenting accuracy checks and calibration adjustments, the calibration standard used to perform the accuracy check is critical to supporting the evidential accuracy of test results. Tis article will focus on ethanol gas calibration standards because they are so widely used in workplace alcohol testing programs.
What is an Ethanol Gas Standard? An ethanol gas standard is a compressed gas mixture that contains a precise amount of ethanol gas and an inert gas, typically nitrogen. Ethanol gas standards go by a variety of names: “dry gas,” “gas tanks,” “alcohol gas tanks,” and “gas canisters,” to name a few. We’ll use the name convention of “ethanol gas standards” to be as clear as possible.
What’s on the Label? An ethanol gas standard is labeled with the BrAC level of the tank as well as the margin of error allowed by the manufacturer of the gas, e.g., 0.038 ± 0.002 BrAC. (See Figure 1) For every practical purpose the operator disregards the margin of error and uses only the stated value of the tank. In other words, the operator does not add or subtract the margin of error from the results of
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an accuracy check. Most manufacturers also include the ppm (parts per million) ethanol concentration. Te manufacturer uses ppm to calculate the amount of ethanol required to produce the desired BrAC concentration.
Evidential Quality = N.I.S.T. Traceability A calibration standard that is “NIST traceable” has the highest level of evidential quality. Te National Institute of Standards and Technology (NIST) is the ultimate authority for every measurement standard in the USA, including breath alcohol calibration standards. NIST produces and sells reference standards that manufacturers and laboratories purchase to ensure the highest level of accuracy in their quality assurance and manufacturing processes. “NIST traceable” means that the
manufacturer of an ethanol gas standard can document the specific NIST reference standards used in the manufacture of each gas tank. Manufacturers can provide that information in a Certificate of Analysis for a particular ethanol gas tank. Te issue of NIST traceability may not come up oſten in defending workplace alcohol test results, but it is very important in supporting alcohol testing performed by law enforcement for DUI enforcement. (See Figure 2)
Corrected vs. Uncorrected? “Uncorrected” ethanol gas is manufactured using a scientific formula based on the Ideal Gas Law and Dalton’s Law of Partial Pressures1
to produce the desired ppm (parts
per million) ethanol vapor concentration. Te scientific formula that predicts the ppm of ethanol to generate the desired BrAC works
Winter 2016
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