A Breath Alcohol Test (BAT) estimates a person’s blood alcohol content (BAC) by analyzing a breath sample. This non-invasive test quickly indicates alcohol impairment.
How the BAT Test Works
When alcohol is consumed, it’s absorbed into the bloodstream and circulates throughout the body, reaching the lungs. In the lungs, alcohol evaporates into the air within tiny air sacs called alveoli.
As a person exhales, this alcohol-laden air from the deep lungs (alveolar air) is expelled. Breath alcohol testing devices capture and analyze this air, as its alcohol concentration is directly proportional to the blood alcohol concentration.
Many modern breath alcohol devices utilize fuel cell technology. In a fuel cell breathalyzer, alcohol in the breath sample reacts chemically with a platinum electrode, producing an electrical current. The strength of this current is proportional to the alcohol amount. Other devices use infrared spectroscopy, where infrared light is passed through the breath sample. The amount of light absorbed at specific wavelengths indicates the alcohol concentration, as this absorption is unique to alcohol molecules.
Different Types of BAT Tests
Preliminary Breath Tests (PBTs) are handheld devices used by law enforcement at roadside stops. They provide an immediate, less precise indication of alcohol presence, helping officers establish probable cause. PBT results are not typically admissible as direct legal evidence.
Evidential Breath Tests (EBTs) are more sophisticated instruments found in police stations. These highly accurate devices are regularly calibrated, and their results are often admissible as legal evidence. BATs are also used in workplace screening and ignition interlock devices, which prevent a vehicle from starting if the driver’s breath alcohol concentration exceeds a pre-set limit.
Understanding Test Results
The numerical result of a Breath Alcohol Test is expressed as Blood Alcohol Content (BAC), representing the amount of alcohol in a person’s blood. For example, a BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood. Although a breath sample is taken, the device converts the breath alcohol concentration (BrAC) into an estimated BAC.
This conversion relies on a scientifically established ratio, often around 2,100:1, meaning 2,100 milliliters of alveolar air contains the same amount of alcohol as 1 milliliter of blood. BAC levels correlate with varying degrees of impairment; lower BAC indicates less impairment, while higher levels suggest significant impairment of cognitive and motor skills. Different legal limits apply depending on jurisdiction and context.
Factors Influencing Accuracy
Several factors influence the accuracy of a Breath Alcohol Test result. “Mouth alcohol” can lead to falsely elevated readings, occurring when alcohol from recent consumption, mouthwash, or conditions like GERD is present in the mouth or upper airway. To minimize this, operators observe a waiting period before testing.
Certain medical conditions, such as diabetes, can also affect results; individuals might produce acetone on their breath, which some older breathalyzers could misinterpret as alcohol. Proper calibration and maintenance of the device are crucial, requiring regular checks for consistent measurements. The operator’s adherence to proper administration procedures, like ensuring a deep lung sample, also plays a role in accuracy.