One of the most common causes of falsely high breathalyzer readings in DUI cases is the existence of mouth alcohol.
The breathalyzer’s internal computer is making a major assumption when it captures a breath sample and then analyzes it for blood alcohol concentration (BAC): It assumes that the alcohol in the breath sample came from alveolar air — that is, air exhaled from deep within the lungs. Since we are trying to measure how much alcohol is in the DUI suspect’s blood, rather than in the breath, the computer applies a formula to translate the results. This formula is based upon the average ratio of alcohol in the breath to alcohol in the blood. This so-called partition ratio is 1 to 2100 — that is, in the average person there will be 2100 units of alcohol in the blood for every unit measured by the breathalyzer in the breath. Put simply, the machine’s computer multiplies the amount of alcohol detected in the drunk driving suspect’s breath sample by 2100 and reports that as the blood alcohol level.
But what if the alcohol in the sample is not from the lungs?
Too bad: the breath-testing machine doesn’t know any better. If there is even a tiny amount of alcohol in the DUI suspect’s mouth or throat, it will be tremendously magnified by the breathalyzer and it will report a much higher breath alcohol concentration than the true one.
Alcohol can be found in the mouth for a number of reasons. The most obvious is that the individual has recently consumed some alcohol; it usually takes 15-20 minutes for the alcohol to dissipate through the rinsing action of saliva. Or the DUI suspect may have recently used mouthwash or breath freshener (most contain fairly high levels of alcohol) — possibly to disguise the smell of alcohol when being pulled over by police. See my post, Breath Fresheners and Breathalyzers.
The most common source of mouth alcohol in DUI cases is from eructation (burping or belching). This causes the liquids and/or gases from the stomach — including alcohol if it is there — to rise up into the soft tissue of the esophagus and mouth, where it will stay until it has dissipated. For this reason, police officers are required to keep a DUI suspect under observation for at least 15 – 20 minutes prior to administering a breath test (in reality, however, many if not most officers are unwilling to stand around watching a suspect for a quarter of an hour).
Acid reflux can greatly exacerbate this problem. As I discussed in another post, GERD, Acid Reflux and False Breathalyzer Results, the stomach is normally separated from the throat by a valve. When this valve becomes herniated, there is nothing to stop the liquid contents in the stomach from rising and permeating the esophagus and mouth. The contents — including any alcohol — is then later breathed into the breathalyzer. Since it has not yet been absorbed through the stomach wall and into the blood and eventually into the lungs, this alcohol should not be read as breath from the lungs and multiplied by 2100. Of course, the breathalyzer doesn’t know this. See the article by Kechagias, et al., “Reliability of Breath-Alcohol Analysis in Individuals with Gastroesophageal Reflux Disease”, 44(4) Journal of Forensic Sciences 814 (1999).
The mouth alcohol problem can also be created in other ways. Dentures, for example, will trap alcohol for much longer than 15-20 minutes. Periodental disease can also create pockets in the gums which will contain the alcohol for longer periods. And so on….
As the American Medical Association’s Committee on Medical Problems warned in its Manual for Chemical Tests for Intoxication (1959): “True reactions with alcohol in expired breath from sources other than the alveolar air (eructation, regurgitation, vomiting) will, of course, vitiate the breath alcohol results.”