Police and prosecutors rely heavily on evidential breath tests, or EBTs, in Florida DUI / DWI cases. However, these tests aren’t as reliable as many people believe. A Florida attorney who focuses on successfully defending drunk driving cases can effectively challenge the results of EBTs and other chemical tests used to determine blood alcohol content (BAC).

A thorough understanding of how alcohol enters the breath is useful to understand how EBT results can be challenged. When a person takes a drink, the alcohol is not digested like other substances – it is absorbed into the stomach and small intestine.  From there, alcohol enters the bloodstream. 

Once alcohol enters the bloodstream, it is distributed to every bodily tissue and organ that contains water.  The blood is carried by the veins to the lungs, where it becomes oxygenated.  The lungs are constructed of air pockets, which are surrounded by blood-rich membranes that expose the lung tissue to alcohol. 

Once alcohol enters the lungs, it is eliminated through the breath by evaporation.  Evaporation takes place as the alcohol circulating in the blood comes in contact with the blood-rich membranes in the lung tissue. 

EBTs and other infrared breath testing instruments isolate alcohol molecules based on the way they absorb infrared light.  No other molecule absorbs radiation at the exact same wavelengths.  In this way, ethyl alcohol has a distinctive fingerprint. EBTs estimate BAC by measuring the amount of alcohol in the breath via a partition ration.

Many EBT machines have inaccurate results because they aren’t equipped with instruments known as “slope detectors” that detect the presence of mouth alcohol.   Mouth alcohol is the undetected, raw, unabsorbed alcohol in the mouth that falsely boosts the results of the breath test.  Mouth alcohol can stem from many sources, including:

1. Tobacco products
2. A substance ingested prior to the breath test, like mouthwash, breath strips, asthma inhalers, or cough drops or syrups
3. Food in the teeth, particularly bread products containing yeast
4. Burping or regurgitation
5. Gastroesophogeal reflux, also known as GERD
6. Dental work, such as dentures, braces or bridges
7. Mouth jewelry such as tongue piercings

Slope detectors collect a real-time reading of the breath sample, and mouth alcohol generates a different pattern than a normal breath sample.  If no mouth alcohol is present, the EBT device will read a continuous, though not linear, rise in breath alcohol until it reaches a plateau.  If the device detects mouth alcohol, there will be a significant and sudden drop.  A slope detector identifies and reports this drop as mouth alcohol, thus invalidating the result. 

EBT results can also be inaccurate if police don’t wait the proper amount of time before starting the test. Mouth alcohol evaporates after 15 minutes if no additional alcohol is ingested, and if none of the conditions that create it are present.  Police must continuously observe the driver for 15 minutes before giving a breath test.  This observation period cuts down on the possibility of a contaminated sample producing a falsely elevated BAC result.

If a driver is given a breath test, he or she should also be given the option of having a blood test taken for independent testing later on, because a breath sample obviously cannot be retained. When a blood sample is preserved, an independent forensic expert may be able to establish later that the driver’s BAC did not exceed the legal limit.