CMI Inc.

Breath Alcohol Testing Basics

Why Breath Alcohol Analysis?


Breath alcohol analysis was developed as an alternative to more invasive types of testing a person for a volume of alcohol consumption. More simply put, it is much easier to obtain a person’s breath sample than to perform a blood test or asking a subject to urinate into a cup. Unlike other testing methods, breath alcohol testers provide immediate results, and most importantly, breath alcohol analysis is as accurate as other means. Here’s why:

Alcohol is Unchanged into the Bloodstream

Unlike most foods, alcohol requires no digestion by the human body. About 80% of consumed alcohol is absorbed unchanged directly into the bloodstream, primarily through the small intestine. The other 20% is absorbed directly through the mouth, throat and stomach walls. The most significant effect on how the body absorbs alcohol is the quantity of food eaten with or just prior to the consumption of alcohol. A large amount of food in the stomach slows the absorption of alcohol into the body. Conversely, if no food is present in the stomach, the rate of absorption is much faster. Complete absorption of one alcoholic beverage takes about 50 minutes after being drank.

Alcohol is Moved through the Body by the Bloodstream

After being absorbed, alcohol is distributed through the human body by the bloodstream. Blood carries alcohol molecules to the liver, to the right side of the heart, to the lungs, and then to the left side of the heart where it is distributed through the entire body, including the brain. The concentration of alcohol is directly proportional to the body water content of each person. This means that alcohol concentration will vary according to a person’s body weight. As a general rule, the heavier a person, the greater the amount of alcohol that must be consumed to reach a specific alcohol concentration in the body.

Coffee Doesn’t Work!

Alcohol is eliminated by the body in three ways: metabolism, excretion and evaporation. The rate at which these three occur varies from person to person. Roughly 80% of alcohol is eliminated through metabolism in which the liver breaks down the complex alcohol to its basic components of oxygen, hydrogen and carbon. These are then eliminated by the body. Despite the popular belief that coffee will "sober up" someone, it does not. Only time will remove alcohol from the human body. A good rule of thumb is to allow one hour for each drink—characterized as one 12-ounce beer, one glass of wine or one "shot" of hard liquor—consumed.

Alcohol Merges with Breath

Part of the ingested alcohol is evaporated into the breath and then exhaled from the body with every exhalation of breath. This process of eliminating alcohol from the blood works the same way as the body giving off carbon dioxide during the breathing process. The exchange of alcohol from the blood to the breath occurs in the alveoli of the lungs. This is called the deep lung region. The alveoli are small tissue sacs which are richly supplied with blood from the heart. The thin tissue layer between the alveoli and blood capillaries is permeable to certain molecules—the alcohol molecule being one. By diffusion, some of the alcohol molecules in the blood evaporate into the breath.

Henry’s Law

According to Henry’s Law, the concentration of a volatile substance in the air above a fluid is proportional to the concentration of the volatile substance in the fluid. Applying this law, the volatile substance is alcohol, the air above is the alveoli or deep lung air, and the fluid is blood.

Blood Test = Breath Test

The blood:breath ratio of 2100:1 has been widely accepted for use in computing blood alcohol concentration from breath. This means that 2,100 milliliters of deep lung air will contain the same amount of alcohol as one milliliter of blood.

Therefore, a Breath Alcohol Concentration (BrAC) is as accurate as a blood test or a Blood Alcohol Concentration (BAC). A breath alcohol analysis expresses alcohol concentration by indicating a weight by volume relationship. Specifically, the instrument found a weight of alcohol expressed in grams per 210 liters of breath from the person who was tested.

Going Deep

In performing a breath alcohol test, it is important to analyze an alveolar or deep lung air sample. If a deep lung sample in not obtained, the sample analyzed could be diluted with breath of a lower alcohol concentration from the upper respiratorty tract. This would result in a lower than optimum test result. When correctly operated, all results from an Intoxilyzer® breath alcohol instrument will be obtained from a deep lung sample. The instruments require the test subject to blow for a minimum time which ensures that the analyzed sample came from the alveolar air region of the lungs.

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