How Evidential Breath Tests Work

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Evidential breath tests, also known as EBTs, are breath-testing instruments commonly used in California drunk driving investigations. Police and prosecutors rely heavily on EBT results, but they are far from foolproof. A skilled DUI / DWI defense attorney from The Kavinoky Law Firm will use a proven strategy to effectively challenge the results of EBTs.

To see how EBTs can be successfully challenged, it’s helpful to understand how alcohol enters a person’s breath. When an individual takes a drink, the alcohol isn’t digested like other substances – it gets absorbed by the stomach and small intestine. From this point, the alcohol enters the bloodstream.

The alcohol is then distributed by the blood to all tissues and organs that contain water. Veins carry the blood to and through the lungs, where the blood becomes oxygenated. The lungs are made up of air pockets, which are surrounded by blood-rich membranes, thus exposing the lung tissue to the consumed alcohol.

Third, the alcohol is eliminated by the body in the breath by evaporation. Evaporation occurs because the alcohol circulating in the blood comes in contact with the blood-rich membranes in the lung tissue and evaporates. During exhalation, the air is forced out of the lungs and emerges into the breath.

Infrared breath testing instruments identify ethyl alcohol molecules based on the way they absorb infrared light. No other compound absorbs radiation at the exact same wavelengths. In this sense, ethyl alcohol has a distinctive fingerprint.

EBTs measure the amount of alcohol in the breath by a partition ratio and converts it to an estimation of blood alcohol content. The problem with EBTs is that they generally contain instruments that detect the presence of mouth alcohol, commonly referred to as “slope detectors.” Mouth alcohol is the undetected, raw, unabsorbed alcohol in the mouth that falsely elevates the results of the breath test. The sources of mouth alcohol may include:

  • A substance ingested prior to the breath test, like mouthwash, breath strips, cough drops or syrups, or asthma inhalers
  • A substance regurgitated or burped from the stomach
  • A case of gastroesophogeal reflux, also known as GERD
  • Dental work, such as dentures, braces or bridges which trap alcohol
  • Mouth jewelry, such as tongue piercings, which trap alcohol
  • Food in the teeth, especially bread and products containing yeast
  • Tobacco products

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

Another problem with EBTs is that police don’t always follow the proper waiting period before starting the test. Mouth alcohol evaporates after a 15-minute period, as long as no additional alcohol is introduced. Thus, police agencies are mandated to continuously observe the subject for 15 minutes before giving the breath test. This observation period cuts down on the possibility of a contaminated sample producing a falsely high BAC result.

Another issue with EBTs is California’s implied consent statute. According to the California Vehicle Code, a person who drives a motor vehicle is deemed to have given his or her consent to chemical testing of his or her blood or breath for the purpose of determining the alcoholic content of his or her blood, if lawfully arrested for an offense committed in violation of Section 23140 (DUI for those under 21 years of age) or 23152 (DUI) or 23153 (DUI with injury). That means that a driver is only required to consent to a chemical test if arrested. However, police often administer breath tests prior to making an arrest.

Generally, a person has the choice of either a blood or breath test. However, if drugs are suspected the person may have to submit to a blood or urine test. But if only one type of test is available, then the person must submit to the available test. For example, if the person in transported to the hospital, they may have to undergo the blood test because no breath testing machines are present at that location.

Further, according to the California Vehicle Code, the person must be told that failing to submit to a chemical test will result in a fine, suspension or revocation of driving privileges, and mandatory imprisonment.

Finally, if only a breath test is chosen, the driver must be given the choice of having a blood test done in order to retain a sample for independent testing later on, because the breath test does not retain a sample.

Because of the many variables present in EBTs and the regulations governing their use, it is possible to challenge test results in a drunk driving case. Any driver who took a breath test and is facing charges of drinking and driving should consult with a qualified California attorney who specializes in DUI / DWI defense.