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How Long do Breathalyzers Detect Alcohol?

By Dyna Whiting - Updated December 17, 2018
Happy friends toasting wine

A breathalyzer is a standard device for measuring blood alcohol content, or BAC. The more you drink, the longer you must wait for the alcohol to clear your bloodstream. On average, a bottle of beer, a glass of wine, or approximately one shot of vodka or whiskey all contain about half an ounce of pure alcohol, and it takes about one hour for each serving to be eliminated from your body.

Blood Alcohol Level

Alcohol is absorbed into the body at a much quicker rate than food. On an empty stomach, 20 percent of alcohol is absorbed immediately into the bloodstream. Measured scientifically in milligrams and deciliters, the average person's body breaks down alcohol at a rate of 20 to 30mg/dL per hour.

The standard rate of alcohol excretion is 0.015 BAC points per hour. Breathalyzers use BAC to show the current measure of alcohol in your body via a breath analysis.

How Breathalyzers Detect Alcohol

Alcohol is either metabolized by the body or excreted via breath, sweat or urine. Breathalyzers work by measuring the concentration of alcohol in the air exhaled by an individual.

Alcohol concentration of the breath is at around a 2100:1 ratio in relation to the concentration in the blood. Breathalyzers utilize either electrochemical fuel cell sensors, semiconductor oxide sensors or infrared spectrophotometers to identify the alcohol content of an individual's breath and calculate it into a reading as a percentage of blood alcohol content.

Types of Breathalyzers

Electrochemical fuel cell sensors are accurate in addition to being conveniently handheld. A fuel cell in the device measures alcohol levels through a chemical reaction that oxidizes the alcohol present and produces an electrical current. More alcohol equals a greater current and the readings are shown accordingly.

Breathalyzers using infrared spectrophotometers are large, tabletop devices that identify alcohol by the way light is absorbed by the breath sample being examined. These are often only found in research centers or at police stations, because of their size.

Semiconductor oxide sensors are the most recent development in breathalyzer technology. They use an ethanol-specific sensor to measure BAC and are growing in popularity due to their low cost, small size and extremely accurate readings.

The Time Frame for BAC Detection

Breathalyzers are able to detect alcohol for varying lengths of time. For the most part, they can detect even the smallest amount of alcohol in a person's system. However, the concern for most people is that their blood alcohol levels be under the legal limit for being considered intoxicated. In the U.S., 0.08 is considered drunk.

Alcohol leaves the body at the standard rate of 0.015 BAC, so you can determine the number of hours necessary for your body to be free of alcohol by simply taking a breathalyzer reading and dividing it by the standard. For example, if a breathalyzer gives you a BAC reading of 0.150, divide 0.150 by the standard 0.015, which will equal 10. This means that it will take 10 hours for the alcohol to clear your body.

How Accurate Are They?

Breathalyzers are prone to error because they don't measure blood alcohol content directly. Various factors such as body temperature, blood composition, the presence of blood in the mouth or even acid reflux can play a role in creating inaccurate readings. There are also many compounds found in the body, such as ketones, that are chemically similar to alcohol. High levels of such compounds can produce a falsely high reading.

Devices using semiconductor oxide sensors have proven to be the most accurate, with accuracy levels of ±0.01 percent at 0.10 percent BAC.

About the Author

Dyna Whiting has been writing and editing health, science and technology related material for nine years. A lot of her experience was established in producing articles and business documents for organizations that are not proficient in English. She holds a Bachelor of Arts in psychology with a pre-medical background.

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