IAFTC Newsletter. Volume 2. Issue 1. February 24, 2026
Guy Oldaker III, J.D., Ph.D1
1guyoldaker3@yahoo.com; 467 Heritage Drive, Lewisville, NC 27023
This is an open-access article under the CC BY-NC-ND license.
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Abstract
In North Carolina, the admissibility of results from testing for breath-alcohol in driving while impaired (“DWI”) cases depends upon results from checks of the accuracy of Intox EC/IR-II evidentiary analyzers. Accuracy checks use dry-gas standards of known alcohol (technically, ethanol) concentration. By regulation, an analyzer is deemed accurate if the result of the accuracy check either agrees with the expected result or is 0.01 less than the expected result. Expected results depend upon atmospheric pressure, which varies with altitude above sea level. Because of this, expected results must reflect adjustment for altitude when accuracy checks are done at elevations above sea level. Defendants receive test tickets that document the results of accuracy checks. However, test tickets do not report the expected results that are needed for comparison to the accuracy check results printed on test tickets. Consequently, defendants cannot independently assess whether accuracy has been demonstrated. This article shows how analyzer accuracy can be assessed in spite of the lack of information on test tickets. Actual data from a test ticket issued in Yancey County, North Carolina, is used. The assessment demonstrates that, contrary to what normally would be claimed, the analyzer is not accurate. Therefore, the breath alcohol result for this defendant should not be admissible in evidence. In addition, accuracy check records from preventive maintenance of the analyzers used in Yancey County were reviewed. None of the test results for 2023 and 2024 should have been admissible. The forensic reliability of past and present breath-alcohol test results from analyzers used in the Mountain and Piedmont Regions of North Carolina requires scrutiny.
Introduction
The subject of this article is the accuracy check of the Intox EC/IR-II analyzer [1] when used in North Carolina for DWI prosecutions. Forensic scientists dealing with breath-alcohol measurements in North Carolina need to be aware of a potential question of forensic reliability when measurements are done at elevations above sea level in the Piedmont and Mountain Regions. Here, forensic reliability means whether measurements satisfy legal rules dealing with evidentiary admissibility.
This article identifies the statute and regulations defining forensic reliability; the data supplied to defendants; the application of the Ideal Gas Law and the Barometric Formula; and procedures for assessing whether reported results are, in fact, forensically reliable. The article is written for a broad audience. Forensic scientists are the main group. However, forensic scientists often will be serving as expert consultants or witnesses in assisting attorneys. Because of this, the article tries to bridge the gap between science and law. At times, concepts are presented in a manner reflecting direct examination as well as legal analysis. In addition, an attempt has been made, to the extent practicable, to simplify so as to make the concepts easier to understand by factfinders, who, in North Carolina, can be either judges or laypersons serving on a jury.
Brief Description of the Analyzer
In North Carolina, the Intox EC/IR-II is the evidentiary analyzer used for DWI prosecutions [2]. In certain respects, this analyzer is unique to North Carolina. This uniqueness is because Intoximeters, the manufacturer of the Intox EC/IR-II, configures the analyzer to an individual state’s requested specifications. Consequently, although many of the basic functions of the Intox EC/IR-II remain the same from state to state, the operation and outputs can differ substantially. To take one example, in Arkansas, the Intox EC/IR-II prints results to three decimal places [3]. By contrast, for North Carolina, the analyzer reports all alcohol concentration measurements truncated to two decimal places. For example, 0.079 truncates to 0.07.
The main components of North Carolina’s Intox EC/IR-II analyzer are an infrared sensor, an electrochemical sensor, a flow sensor, and an atmospheric pressure sensor (a barometer) [4]. The infrared sensor and flow sensor operate together. Their two functions are to alert to mouth alcohol and to determine when an appropriate sample has been obtained for analysis. With an appropriate sample acquired, a small portion (about 1 mL) is directed to the electrochemical sensor. The analysis of alcohol takes place at the electrochemical sensor.
A key function of the barometer is to account for the effect of atmospheric pressure on the alcohol concentration of the dry-gas standard when the analyzer’s calibration is checked [3, 5]. The check uses (as a reference material) a mixture of alcohol (specifically ethanol) with a known concentration in nitrogen gas. This mixture is contained and compressed in a small tank. North Carolina calls the tank a “gas canister”[6]. The gas canister is located in a locked compartment within the analyzer and cannot be seen during normal operation. North Carolina refers to these calibration checks as “accuracy checks” [7].
North Carolina’s Rules for the Accuracy Check
One statute and two regulations govern forensic reliability and acceptance criteria for the accuracy check, respectively. North Carolina General Statutes § 20-139.1(b)(1) addresses forensic reliability, that is, whether results are admissible in evidence: “A chemical analysis of the breath administered pursuant to the implied-consent law is admissible in any court or administrative hearing or proceeding if . . . [i]t is performed in accordance with the rules of the Department of Health and Human Services.”
The pertinent rules are contained in two regulations. One regulation supplies the criterion for forensic accuracy: the analyzer “shall be deemed accurate” if the result of the accuracy check is either “obtaining the expected result or 0.01 less than the expected result as specified in Item (10) of this Rule” [7]. The other regulation, Item (10), stipulates that the sample provided by the gas canister “corresponds to the equivalent concentration of 0.08” [6]. (Units of g/210 L are implied for the 0.08 value. This article follows this convention.) No statute or regulation supplies guidance on the interpretations of the terms “expected result” and “equivalent concentration.”
Critically, in court proceedings throughout North Carolina, an accuracy check result of either 0.08 or 0.07 is presently assumed to establish that an analyzer is accurate, and therefore, its results are forensically reliable and admissible in evidence.
Operation of the EC/IR II
The Forensic Tests for Alcohol Branch (“FTAB”) of the North Carolina Department of Health and Human Services has general responsibility for the analyzers. Based upon the absence of published documentation, it appears that FTAB uses the analyzers “as received.” With the sole exception of the accuracy check, there is no indication that FTAB checks the calibration of any of the analyzer’s sensors, including the barometer. FTAB reports no quality assurance plan that would include checking the output of any sensor over its expected measurement range [8].
Ordinarily, law enforcement officers, who, by regulation, are termed “chemical analysts,” [9] operate the analyzers when a subject’s breath-alcohol is tested.
Figure 1 is a copy of an actual test ticket that a defendant received when breath alcohol was tested. With the exception of identifying information, which has been redacted, this test ticket is representative of all test tickets currently issued in North Carolina. The test ticket is the sole source of information about the breath-alcohol analysis and accuracy check, which is abbreviated ACCY CHK on the test ticket. This defendant received nothing else. Noteworthy is the fact that Yancey County is located in North Carolina’s Mountain Region. Burnsville, the county seat, is at an elevation of 2,749 feet above sea level.
The result of the accuracy check was 0.08. Based upon custom and a facial interpretation of the regulation, law enforcement, defendants, and their counsel would all reasonably conclude that this result demonstrates that the analyzer “shall be deemed accurate.” As will be explained below, this conclusion is wrong. Indeed, quite the opposite is true: The analyzer should be deemed not accurate. The result for this defendant’s breath-alcohol concentration is not forensically reliable. The result should not be admissible in evidence.
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