Mouth alcohol is one of the leading causes of false blood alcohol concentration readings in breathalyzer tests. To understand why mouth alcohol can produce false breathalyzer readings, we have to understand a little about how a breathalyzer works.
How Breathalyzers Work: the breathalyzer internal computer makes a major assumption when measuring blood alcohol content (BAC). It assumes that the breath sample that is tested consists of uncontaminated alveolar air – that is, that the sample is air from deep within the lungs and does not contain anything else. Since we are trying to measure how much alcohol is in the blood (rather than in the breath) the breathalyzer applies a formula to translate the input into BAC. The formula is based upon the average ratio of alcohol in breath to alcohol in blood. This ratio is 1 to 2,100, i.e. in the average person there will be 2,100 units of alcohol in the blood for every unit detected by the breathalyzer in the breath. In other words, the machine multiplies every unit of alcohol detected by 2,100 in order to give the readout of blood alcohol concentration.
But how does the breathalyzer know that the alcohol detected came from the lungs? It doesn’t. Any alcohol detected is assumed to be from the lungs. This means that even if there is even a miniscule amount of alcohol in the suspects mouth or throat, it will be tremendously magnified by the breathalyzer formula and report a much higher BAC than the the true one.
Mouth Alcohol: this is simply residual alcohol in the throat or mouth that may contaminate the breathalyzer sample. So what are some causes of mouth alcohol? The most obvious is that an individual has recently consumed some alcohol. Typically, it takes 15-20 minutes for alcohol to dissipate through the rinsing action of saliva. Alternatively, the individual may have recently used breath freshener or mouthwash (perhaps in an effort to conceal the smell of alcohol after being pulled over by the police). Most mouthwashes and breath fresheners contain fairly high levels of alcohol.
The most common source of mouth alcohol is eruction (burping or belching), where liquids and/or gases from the stomach (including alcohol and alcohol vapors) to rise up into the throat and mouth where they will stay until they have dissipated. Acid reflux can exacerbate this problem. Further, mouth alcohol can be created by other means. For example, dentures or caps can retain small amounts of alcohol. Thus, it is important that you tell your DWI attorney of any relevant medical or dental history. Depending on how the test was administered to account for the possibility of mouth alcohol, your DWI attorney can challenge the admission of the breathalyzer test results at trial.
