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One of the most common causes of falsely high breathalyzer readings is the existence of mouth alcohol.

A breathalyser assumes is that the alcohol in the breath sample came from alveolar air (air exhaled from deep within the lungs). However, alcohol may have come from the mouth, throat or stomach for a number of reasons.

Passive testing devices are extremely susceptible to these issues. To help prevent mouth-alcohol contamination, certified breath-test operators are trained to observe a test subject carefully for at least 15-20 minutes before administering the test. Additionally, all professional breathalyzers require the subject to blow throw a tube or mouthpiece to produce a specific sample size from which the concentration is devolved.

The problem with mouth alcohol being picked up by the breathalyzer is that it was not alcohol absorbed by the stomach and passed through the blood to the lungs. In other words, the machine’s computer is mistakenly applying the partition ratio and multiplying the result. Consequently, a very tiny amount of alcohol from the mouth, throat or stomach can have a significant impact on the breath-alcohol reading.

Other than very recent drinking, the most common source of mouth alcohol is from belching or burping. This causes the liquids and/or gases from the stomach, including any alcohol, to rise up into the soft tissue of the oesophagus and oral cavity, where it will stay until it has dissipated. For this reason, police officers are supposed to keep a drink driving suspect under observation for at least 15 minutes prior to administering a breath test.

Mouth alcohol can also be created in other ways.

  • Dentures, for example, can trap alcohol.
  • Periodontal disease can create pockets in the gums which will contain the alcohol for longer periods.
  • Recent use of mouthwash or breath freshener containing fairly high levels of alcohol.

The only approved instrument currently available that is certified to detect mouth alcohol is the Draeger 7510, released in 2010.