Case Study - A Personal Breath Tester
Part 1: Interpretation of a false-positive result
From - Counterpoint Volume 3: Issue 3 - Article 1 (December 2018)
An article for participants in the myCAMprogram
Jan Semenoff, BA, EMA
Forensic Criminalist
Article information:
650 words (approximately 4-8 minutes)
A Personal Breath Tester was being used for court-ordered compliance in a family law case. The father was accused of long-term alcohol abuse, and his ex-spouse demanded monitoring as a condition of his visitation rights. Two positive results were reported. If accepted as valid, they could have led to his visitation being cancelled over Christmas until he could prove compliance with a zero-consumption order.
I received the request for review on a Wednesday night, with an emergency affidavit due Friday at noon — meaning no time to request the device’s calibration and maintenance records, which would normally be essential for confirming accuracy. I had to rely solely on the transmitted breath test logs.
How Personal Breath Testers Work
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Personal Breath Testers (PBTs) are compliance monitoring breath alcohol testing device that utilizes three combined components:
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Because they uses a fuel cell sensor, PBTs cannot include a “Residual Alcohol Detection System” (RADS) or slope detector to distinguish between alcohol from recent drinking and alcohol from mouth contamination (e.g., mouthwash). The manufacturer warns about this in its guidelines and lists products that may cause false positives.
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Event timeline
Examining Non-Compliance Reports
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From months of prior random testing (>100 samples), two clear false-positive events stood out. We’ll examine the first.
Test #102 – 11:46 p.m. previous night – Result: 0.000 g/dL Test #103 – 6:48 a.m. next morning – Result: 0.114 g/dL Test #107 – 8:26 a.m. same morning – Result: 0.000 g/dL Between Test #102 and Test #103, more than 7 hours elapsed. Between Test #103 and Test #107, only 1 hour 38 minutes elapsed. |
By education, experience and training, I am primarily an investigator. Investigators should rely upon as complete a picture as possible in order to arrive at an investigative conclusion. This involves a complete data set from the breath testing device, including any calibration and error logs. I would really have liked to examine these calibration and error logs so that we could verify or refute the data to examine the reliability of the reported breath alcohol test results. Unfortunately, due to the time constraints, we couldn’t get access to the calibration logs. The transmitted results of the device itself would have to suffice.
The first event
By looking at these transmitted breath test results, in log form going back several months prior to the incident before the court where the subject had provided more than 100 random breath samples, I could tell there were two specific instances where the device had clearly provided false data. We will discuss the first event in this article, and the second in Part 2.
An Important Note:
I want to make clear that this first event does NOT indicate a mistake, failure, or error on the part of the PBT device, but rather, identifies sub-standard conditions that created a false-positive reading that were dependent upon proper analysis and understanding of the circumstances. This is a failure of interpretation of the readings, not the device itself, of the reported BrAC readings.
I want to make clear that this first event does NOT indicate a mistake, failure, or error on the part of the PBT device, but rather, identifies sub-standard conditions that created a false-positive reading that were dependent upon proper analysis and understanding of the circumstances. This is a failure of interpretation of the readings, not the device itself, of the reported BrAC readings.
What happened?
Circumstances leading up to a false-positive result:
The subject had just brushed his teeth in the morning then was summoned by the device for a breath sample. His reported reading was 0.114 g/dL which promptly disappeared by the time of his next breath test 90 minutes later. This yields a physiologically impossible elimination rate of 0.070 g/dL per hour, therefore had to be a false positive due to fresh mouth alcohol from the toothpaste. Obviously, the device didn’t know the toothpaste contained mouthwash, and therefore an amount of ethanol. The assumption made was that the reading reflected beverage alcohol consumption. However, the data supports a different conclusion…
Here is an excerpt of the disclosed logs:
Here is an excerpt of the disclosed logs:
The night before, a breath test (#102) was obtained at 2346 hours with a reported reading of 0.000 (zero) grams. Slightly more than 7 hours then elapsed before the next required breath test (#103), which was obtained at 0648 hours the next morning with a reported value of 0.114 g/dL.
Reported reading: what could explain it?
If we assume the 0.114 g/dL at 6:48 a.m. was accurate, only one of three scenarios must be true:
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Scenario 1 and 2 represent the extreme possibilities. Let’s look at each in turn to see if they make sense...
First, why did I use 0.117 g/dL in my calculations above? It has to do with his weight...
First, why did I use 0.117 g/dL in my calculations above? It has to do with his weight...
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The test subject is an adult male who weighed about 220 pounds and stands 6’2” in height. A male of that height and weight will receive the BAC equivalent of 0.017 grams/100ml of blood for each Standard Drink consumed.
Standard Drinks are defined as follows:
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Why these scenarios are implausible
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In all scenarios, the follow-up test 1 hour 38 minutes later is the problem.
His BAC dropped from 0.114 g/dL to 0.000 g/dL — an elimination rate of 0.070 g/dL/hr. This is 3.5–7 times faster than any documented physiological rate (normally 0.010–0.025 g/dL/hr, with an extreme upper bound of 0.045). Such a drop is impossible through metabolism alone. What happened? Stay tune for Part 2… |
Logical conclusion:
Because the drop was too fast to be real, the most reasonable explanation is mouth alcohol contamination. The subject reported brushing his teeth shortly before the test. Toothpaste containing mouthwash (and thus ethanol) could leave residual alcohol in the mouth that a fuel cell detects as beverage alcohol. With no slope detector, Soberlink cannot distinguish this.
The 20-minute wait time before testing (per the manufacturer’s guide) was not met here — a sub-standard condition that renders the reading forensically unreliable.
Takeaway:
In forensic alcohol testing, reliability is digital — either a reading meets all procedural and environmental standards, or it must be considered unreliable. In this case, the facts point clearly to contamination, not consumption.
Send me your questions or comments:
Comments and questions will be posted here with their responses:
Comments and questions will be posted here with their responses:
For further study:
- Dubowski, K.M., Acceptable Practices for Evidential Breath-Alcohol Testing, Center for Studies of Law in Action, Borkenstein Course Materials, Indiana University, May 2008.
- Dubowski, K.M., Quality Assurance in Breath-Alcohol Analysis, Journal of Analytical Toxicology, Vol. 18, Oct 1994.
- Gullberg, R. G., Breath Alcohol Measurement Variability Associated with Different Instrumentation and Protocols, Forensic Science International 131 (2003) 30-35.
- Jones, A. W., Concerning Accuracy and Precision of Breath-Alcohol Measurements, Clinical Chemistry, 33/10, 1701-1706 (1987).
- Jones, A. W., Evidence-Based Survey of the Elimination Rates of Ethanol from Blood with Applications in Forensic Casework, Forensic Science International 200, 1-20 (2010).
- Soberlink Cellular Device Quick Start Guide, Soberlink Healthcare LLC, 2016.
- Sterling, Kari, The Rate of Dissipation of Mouth Alcohol in Alcohol Positive Subjects, The Journal of Forensic Science, 2011.
