The term BrAC stands for Breath Alcohol Concentration, which is the amount of alcohol present in a person’s exhaled breath. This measurement is the foundational metric used by breathalyzer devices to determine the physiological presence of alcohol in the body. The BrAC reading serves as a rapid, non-invasive method to estimate the Blood Alcohol Concentration (BAC), which is the standard legal metric for intoxication.
What Breath Alcohol Concentration Measures
Breath Alcohol Concentration is a direct measurement of the alcohol content in an individual’s deep lung air. This figure is then used to calculate the Blood Alcohol Concentration (BAC), which represents the weight of alcohol per volume of blood. BrAC is typically expressed as grams of alcohol per 210 liters of breath, a unit established to align with the estimated blood alcohol level.
The relationship between BrAC and BAC is based on a scientific principle called the partition ratio. This ratio, widely accepted as 2100:1, means that 2,100 milliliters of alveolar air are expected to contain the same amount of alcohol as 1 milliliter of blood. Breathalyzer devices use this fixed conversion rate to translate the measured breath alcohol into the legally relevant BAC percentage.
How Alcohol Enters the Breath
The presence of alcohol in a person’s breath is the result of absorption and gas exchange that occurs within the body. After alcohol is consumed, it is absorbed primarily through the small intestine and stomach into the bloodstream. The blood then circulates the alcohol throughout the body, including to the lungs.
Within the lungs are millions of tiny air sacs known as alveoli, which are surrounded by a network of capillaries. This is where gas exchange happens. Since alcohol is a volatile substance, some of the circulating alcohol transfers from the blood into the air of the alveoli through passive diffusion. This alcohol-infused air is known as deep lung air, and its concentration is measured by a breathalyzer when a person exhales.
Legal Limits and Impairment Levels
BrAC and its converted BAC are used to define the legal and medical boundaries of alcohol impairment. In the United States, the standard legal limit for operating a motor vehicle is a BAC of 0.08% in most states. At this level, a person is considered legally intoxicated, with measurable impairment in balance, speech, vision, and reaction time.
Even at lower concentrations, alcohol affects the central nervous system, causing measurable changes in behavior and coordination. A BAC of 0.02% may cause an altered mood, relaxation, and a slight loss of judgment, while 0.05% leads to lowered alertness and impaired judgment. Levels of 0.15% result in significant loss of balance, nausea, and vomiting. Beyond driving, BrAC/BAC measurements are also employed in workplace safety policies, medical diagnostics for alcohol poisoning, and in legal contexts requiring a determination of sobriety.
Variables That Affect Breath Alcohol Readings
Several factors can influence a breath alcohol reading, sometimes causing the result to differ from the actual blood alcohol concentration. One significant issue is “mouth alcohol,” which occurs when residual alcohol is present in the mouth or upper airway rather than originating from the deep lung air. This can be caused by recent consumption of alcoholic beverages, mouthwash, breath sprays, or certain medications that contain alcohol.
Physiological conditions can also alter the breath test results, such as gastroesophageal reflux disease (GERD), which can bring alcohol vapors up from the stomach and lead to a falsely high reading. Furthermore, a person’s breathing pattern immediately before the test can change the outcome; hyperventilating tends to lower the reading, while holding one’s breath can temporarily increase it. Individual metabolic rate, body temperature, and certain medical conditions like diabetes also play a role.