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Understanding BAC and breathalyzers

On Behalf of | Sep 9, 2020 | DUI

Law enforcement in Minnesota uses breathalyzers to check Blood Alcohol Content, or BAC. A higher amount of alcohol takes longer to get expelled from the bloodstream. It commonly takes one hour for an ounce of alcohol to leave the body. An ounce of pure alcohol equals one shot of whiskey or vodka.

Understanding blood alcohol content

The body absorbs alcohol faster than food, absorbing 20% on an empty stomach. The average person breaks down alcohol at a rate of 20-30 mg/dL per hour. Alcohol excretes at an average rate of 0.015 BAC points each hour.

How breathalyzers work

The breathalyzer records the amount of alcohol in the bloodstream by having the person blow into it. The BAC between the breath and the amount absorbed by the bloodstream has a ratio of 2100:1. The device measures BAC by semiconductor oxide electrochemical fuel cell sensors, or infrared spectrophotometers.

Infrared spectrophotometers is a large table device that measures BAC by using the amount of light energy that passes through the breath sample. Due to the size, they are more often seen in police stations.

Electrochemical sensors are handheld devices that measure the BAC by oxidation of the alcohol with an electrical current. Semiconductor oxide sensor devices are the latest breathalyzer technology that uses an ethanol sensor.


Though breathalyzers can detect small amounts of alcohol at various time periods, they don’t directly measure BAC, which could lead to errors. Many factors can impact the reading, such as blood structure and body temperature. Acid reflux, blood in the mouth, and ketones may also affect readings. Semiconductor oxide conductors are considered to be the most accurate.

The allowed BAC level in most all states in .08. A BAC reading over .08 could lead to a DUI. If the driver feels the breathalyzer is incorrect, a DUI attorney may be able to help prove their case.


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