Evidential breath tests, commonly known as EBT’s, are the most commonly used breath-testing instruments. These instruments detect ethyl alcohol by infrared spectroscopy.
How alcohol gets in the breath
First, a person ingests an alcoholic drink. The alcohol does not get digested like other substances, but instead gets absorbed by the stomach and small intestine. From this point, the alcohol enters the bloodstream.
Second, the alcohol is distributed by the bloodstream to all bodily 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 called alveoli. The alveoli 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 (alveoli) and evaporates. During exhalation, the air is forced out of the alveoli and emerges from the lungs into the breath.
EBT’s measure the amount of alcohol in the breath by a partition ration, converting it to an estimation of blood alcohol content.
The Science Behind Infrared Technology
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."
Infrared instruments measure energy entering a vapor-filled sample chamber inside the EBT machine. When the energy beam emerges from the sample chamber, the EBT machine measures the resulting energy loss reflecting the unique fingerprint of ethyl alcohol. The more ethyl alcohol is present, the greater the degree of absorption and the more infrared energy loss. This energy loss is then calculated to give a blood alcohol content (BAC) determination. The breath sample is calculated as a blood alcohol level by applying an average blood-to-breath partition ratio of 2100:1. The average temperature of breath as it leaves the mouth is 34 degrees Celsius. At this temperature, research has shown that 2,100 milliliters of deep lung air contains the same quantity of alcohol as one milliliter of blood. Thus, EBT’s calculate the amount of alcohol per 210 liters of air.
EBT’s 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, asthma inhalers, and many others
§ 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 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.
Required 15-Minute Observation Period
Science has proven that mouth alcohol evaporates after a 15 minute period, so 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.
Implied Consent Admonition
According to California Vehicle Code section 23612, 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).
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 Section 23612, 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 then the person 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. |
