This phenomenon is known as residual mouth alcohol. And it can affect the reliability of an approved screening device (or, roadside breathalyser) test. But it can also affect the reliability of a breathalyser at the police station, even where the instrument has a mechanism designed to eliminate it.
The video above shows how mouth alcohol falsely skews the results. I do not want to spend much time on the process, but more on what I have seen and where mouth alcohol can come from in affecting a breath test.
What is Mouth Alcohol
Put simply, mouth alcohol is residual alcohol remaining in the mouth and lining of the oesophagus following recent consumption of alcohol. Generally speaking, it takes fifteen minutes from the time of last drink to eliminate residual mouth alcohol, though in certain circumstances it has been demonstrated that contamination by residual mouth alcohol can last significantly longer.
Mouth alcohol will always falsely elevate a breath test result. A person with a lawful blood alcohol level, as I have in the video above, will have their mouth alcohol result added to their underlying BAC to produce a high reading. Mouth alcohol will never produce a falsely lowered breath test reading.
Sources of Residual Mouth Alcohol
The most common source for residual mouth alcohol contamination is a recent drink of alcohol. It takes fifteen minutes for residual mouth alcohol to dissipate from the mouth, which means that if the roadside breathalyser test is conducted too quickly after the last drink then the results may produce a false positive.
This can pose a particular problem in roadside breath testing investigations. We are all aware of the phenomenon of people who drink while they are driving their vehicles. In those cases, if the officer discovers open liquor and does not take steps to address mouth alcohol, or if they do not know about it and therefore do not take the necessary precautions, then the test will be falsely high and unfair to the driver. So police are trained to exercise care when taking breath samples. That does not always happen. And often they are unaware of sources of residual mouth alcohol.
There are also cases where the police do not turn their mind to the issue. Take, for example, Mr. Bensmiller, who was stopped leaving a pub. He admitted consuming alcohol but the police did not wait fifteen minutes or ask about mouth alcohol consumption. The Court found that not waiting or even asking in those circumstances was “akin to wilful blindness.”
But mouth alcohol can also come from other sources. A recent burp, belch, or regurgitation or vomit can cause mouth alcohol contamination. This is particularly concerning in cases of GERD, commonly known as acid reflux. People who suffer from this condition may produce false positives on breathalysers because of the acid build-up in the oesophagus that contains alcohol from the stomach. Regurgitated stomach contents containing alcohol will cause false positives.
Police are trained to watch for burping, belching, vomiting, or regurgitation but this is not always visible, particularly in cases of those who suffer GERD. Burping can often be concealed and done silently, such that a less-than perfect observation can miss the occurrence of a burp, which then affects the test result.
Even still, there are lesser-known causes of residual mouth alcohol. For example, some asthma inhalers contain an alcohol-based propellant (Salbutamol 100ug HCG ventalin inhalers, for example, contain ethanol in the propellant) which can skew results if used within fifteen minutes of the test. Many smokeless chewing tobaccos contain ethyl alcohol to prevent the tobacco from drying out, and so a waiting period is required after chewing tobacco is removed from the mouth.
There are also candies and cough syrups that contain alcohol. However, fuel cell devices like roadside breathalysers are ethanol-specific. Methanol, as often found in cough drops, will not cause false readings. Alcohol can also become trapped in objects in the mouth. Chewing gum will trap alcohol, as well dentures, invisalign braces, and mouth guards. So sources an officer may not even see or know about could raise significant concerns about residual mouth alcohol.
But this Doesn’t Affect Criminal Cases, Right?
Mouth alcohol can absolutely affect criminal cases. Although most criminal impaired driving cases involve breath tests done on an approved instrument at the police station, this does not rule out the possibility of mouth alcohol contamination.
The breathalysers used at the police station in criminal investigations are designed to detect mouth alcohol. They do this using something called a “slope detector.” Essentially, a proper breath sample will form a parabola-shaped curve as the level rises while deep lung air is collected, then plateaus once deep lung air is obtained, and then tapers off as blowing tapers off. If there is a rapidly declining alcohol level detected by the instrument, the device is designed to abort the test due to mouth alcohol concerns.
However, this is not foolproof. Not only does the Intox EC/IR II manual (the current breathalyser) clearly indicate this to be the case, but I have demonstrated that it is possible to obtain pure mouth alcohol readings on the most sophisticated, newest approved instrument: the Datamaster DMT.
Last summer, I was able to obtain readings as high as 15 mg% just from a tiny sip – less than a thimble – of vodka which I swallowed a few minutes before blowing. You can download the tickets produced by the machine, graphing my results, below. And although this instrument brags that it is capable of detecting and ruling out mouth alcohol, the charts and graphs that were produced clearly showed that I was providing a sample falsely elevated by residual mouth alcohol.
The presumption of innocence is important. And protecting it begins with understanding what can go wrong in an impaired driving case. Residual mouth alcohol is a significant factor.