How Breathalyzers Work (and Why They Don’t)
Posted by Lawrence Taylor on May 6th, 2005Did you ever wonder how breathalyzers work? There is a website which will give you a pretty fair idea. But first, let’s clear up some confusion….
There are many different kinds of “breathalyzers” — or, more accurately, there are many kinds of breath testing devices. The first of the modern breath testers, manufactured by Smith and Wesson many years ago (yes, that Smith and Wesson), was called the Breathalyzer. Since then, various manufacturers have recognized the growing market and come out with their own models, bearing such names as Intoxilyzer, Intoximeter, DataMaster, AlcoSensor, Alcotest and so on; most of these products have been produced in different model versions, such as the Intoxilyer 4011, 5000 and 8000.
To deal with the confusion, the term “breathalyzer” came to be used as a generic term for any breath testing instrument. (To confuse things further, a German company — Draeger — bought the rights to the Breathalyzer brand and have sometimes used that name in some of their models.)
Most of these are evidentiary machines — that is, larger machines generally kept at the police station whose test results are used in evidence. Others are smaller, handheld units carried by officers in the field; generally called PBTs (preliminary breath tests) or PAS (preliminary alcohol screedning), these are less accurate and are usually used as a field sobriety test to help determine whether to arrest a suspect.
The original Breathalyzer operated using a wet chemical method of analysis, employing a disposable glass ampoule of chemicals. Although still occasionally found in law enforcement, this relatively primitive technology was replaced in later machines by infrared spectroscopy, gas chromatography or, mainly in handheld units, fuel cell analysis; a couple of the more recent machines use a combination of infrared and fuel cell.
Now that this has been cleared up, you might want to visit the following sites to understand the actual workings of these gizmos:
Chemical (the Breathalyzer)
Infrared spectroscopy (the Intoxilyzer)
Fuel cell (the Alcosensor)
Note: Gas chromatography is rarely encountered anymore, as it was primarily used in the discontinued Intoximeter 3000.
Note #2: To further understand why these machines aren’t nearly as accurate as law enforcement would have you believe, visit a few of my previous posts:
Breathalyzers — and Why They Don’t Work
Breathalyzer Inaccuracy: Testing During the Absorptive Stage
Breathalyzer Inaccuracy: Post-Absorptive
Breathalyzer Inaccuracy….It Gets Worse
“Close Enough for Government Work”
Why Breathalyzers Don’t Measure Alcohol
How to Fool the Breathalyzer
Breathalyzers and Radio Frequency Interference
Breathalyzers: Why Aren’t They Warranted to Measure Alcohol?
[…] tests, even though most criminal defense lawyers will tell you the technology is unreliable and not worth risking your liberty over. (Even police officers routinely refuse breathalyzer tests when stopped for […]
In an unpublished opinion issued by the Minnesota Court of Appeals on March 3, 2009 entitled State v. Thompson, Judge Stoneburner affirmed the district court’s denial of an accused drunk driver’s request to obtain and review the source code for the Intoxilyzer 5000 EN.
In Thompson, the driver challenged his conviction of misdemeanor driving while impaired, arguing that the district court abused its discretion in denying his motion to discover the source code for the Intoxilyzer 5000EN. Under the Minnesota Rules of Criminal Procedure, in misdemeanor cases, any discovery beyond police investigatory reports is by consent of the parties or motion to the district court. Under the rule, the district court may exercise its discretion and require the prosecution to disclose material and information if the defendant shows that the information may relate to the guilt or innocence of the defendant or negate the guilt or reduce the culpability of the defendant as to the offense charged.
Thompson argued that the Intoxilyzer was “the State’s only witness†and asserted that he is entitled to “conduct a full examination†of this witness. He argued that he cannot assess the reliability of the testing method without access to the source code. He asserted that he has shown the relevance of the source code to his guilt or innocence in a manner sufficient to make the district court’s denial of its discovery an abuse of discretion. The Court of Appeals, however, disagreed, relying on the State’s expert, who stated:
In the field of forensic toxicology, validation of analytical methodologies for analyzing alcohol and other drugs in the human body is performed exclusively without access to analytical instrument software source code . . . . I have never heard or read of a validation of a toxicological analysis method that was performed with access to the software source code of the analytical instrumentation. I also am unaware of any articles in peer review journals describing the necessity for access to source codes for any validation tests.
Judge Stoneburner opined:
Thompson has not shown the existence of any validation method that requires the source code; has not explained why existing reliability testing (that does not require the source code) is insufficient to establish the reliability of the instrument used in his test; and has not explained how the source code could invalidate existing reliability testing. On this record, we cannot conclude that the district court abused its discretion by denying Thompson’s request for discovery of the source code.
Why do we defense lawyers continue to push for the disclosure of the Intoxilyzer source code? It’s actually pretty simple. The code is the hub between a breath sample and the method by which those samples are afforded a numerical value. Remember your math teacher demanding that you “show your work?” The Intoxilyzer manufacturer (obviously intending to protect what it believes to be valuable intellectual property) continues to refuse to show its work. How, then, can the court understand whether the results offered by a machine are inherently reliable?
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