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Problems with Proving Impairment by Machine

Posted Wednesday, June 13, 2018 by Andrew Charles Huff

There are several ways a person may be found guilty of Driving Under the Influence (DUI) in Washington. First, when a driver’s blood alcohol content (BAC) was .08 or above within two hours of driving. Also, when it’s shown their ability to drive was effected to an appreciable degree by alcohol or drugs.

For years, Washington has measured a person’s Blood Alcohol Content (BAC) with a machine called the DataMaster breath machine. However, this has changed and now the state is switching over to the Draeger Alcotest breath machine manufactured by a German company. In all breath test machine cases including the DataMaster and Draeger Alcotest machine, these machines are located at the station and cannot be used at the arrest scene to obtain a breath sample. Therefore, the time it takes to obtain a sample can take anywhere from 30 minutes to several hours after the person was driving, proving the that the BAC sample does not tell us exactly what the person’s alcohol level was at the time of driving.

When we consume alcohol, it must be absorbed by the body in order to enter a person’s blood system and affect their mental and physical faculties. Once the alcohol is absorbed, it will dissipate, or eliminate, from the blood system and therefore works like a “bell-curve” in a person’s body. But it’s not a perfect bell-curve and the rate at which alcohol absorbs and stays in the blood system varies by the person. This can affect how quickly the alcohol absorbs as well as if there is a plateau period, or time for which the alcohol content remains the same. The average dissipation rate ranges from .015-.020% per hour.

This leads to so many variables, and merely knowing a person’s BAC at a specific time does not tell us exactly what that person’s BAC was at any specific time in the past. This obviously is important because it means, without more information, knowing a BAC at some point in time after a person was driving does not give us enough information to know what that person’s BAC was at the time that person was driving. The fact that blood alcohol dissipates is notable for what it does not tell the court. It does not, for example, by itself inform the court whether at any given time, a person’s blood alcohol is dissipating or increasing. After all, it is also a matter of common knowledge that, before a person’s blood alcohol can dissipate, alcohol must accumulate in the blood.

This is all to say that, just because a person blows .08 or above, it does not necessarily mean that person is guilty of Driving Under the Influence. Much more goes into this question and the prosecutor must present more evidence to the jury to suggest what that specific person’s BAC was at the time that person was driving.

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