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How Do The Machines Actually Measure The Level Of Alcohol?

The machines are fairly accurate, but what they are not necessarily telling you is what the blood alcohol level was at the time when you were driving. If someone blows into this machine, and minutes or hours pass, that does not tell us what the blood alcohol level was of the driver at the time they were driving, and that is precisely what we are trying to do. These machines cannot accurately tell us that number. Now, what they are telling us is what the result is at the time that the person is blowing into the machine, say it is an hour after driving. Someone could have absorbed, or burned off the alcohol by the time they take the test.

In regards to accuracy, you will hear expert witnesses, such as forensic toxicologists that typically say there is a ten percent margin of error some may say less, some may say more. Many different things can go into the accuracy of these machines. They can be anything from body temperature, along with the fact that someone may not be fully absorbed of alcohol at the time that they were blowing into the machine. If that is the case, they would have more alcohol in their core instead of their extremities, and that is a false positive, that could make the result much higher than it actually was at the time of driving.

Therefore, you can have false positives, because the alcohol is not fully absorbed at the time of the test. Full absorption is important, it tells us when someone is fully impaired, or the alcohol they drank is affecting their brain. When it goes to extremities, those are the fingers, toes, and head those are your extremities. So, someone may get pulled over at 10 o’clock at night after having had some drinks, and after they eat, the alcohol has not fully absorbed, and it is more in their core, not their intestines, but it has not reached their bloodstream, which can cause an impairment. Therefore, you have more alcohol in the lung area, which is in your core, which gives you a higher result on a breath test.

When that alcohol has fully dissipated, and it is in the bloodstream, the blood going through the brain affects the brain. When someone takes a breath test, the alcohol is absorbed, and someone might show a 0.06% alcohol level in regards to how much alcohol went through their brain at the time they were driving. Nevertheless, later on, they show a 0.08% alcohol level absorption, because that alcohol has been transported to the extremities.

I am trying to make it as simple as possible, but the bottom line is this, while a machine may give us a number, and have a margin of error, there may be things that affect that number. It still does not tell us what the blood alcohol level was at the time you were driving. We definitely need to know how accurate that number is, and it is completely inaccurate unless someone can tell us that they were fully absorbed at that time.

If someone had an empty stomach, and drank two hours, an hour-and-a-half, or an hour before driving, they are more likely to be fully absorbed and burn off that alcohol at the time they are tested with this breath machine or blood test. Nevertheless, recent drinking or food in the stomach’s absorption can mess with the numbers, and that is what people need to understand. As a juror in a DUI case, we try to make them understand that this is not just black and white; there are variables here, and many defenses that need to be considered, because the burden here is proof beyond a reasonable doubt. If you cannot tell whether someone has fully absorbed, they should not be convicted.

For more information on Measuring Alcohol In Human Body, a free initial consultation is your next best step. Get the information and legal answers you are seeking by calling (415) 523-7878 today.

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Aaron Bortel
With 30 years of specialized experience in DUI defense, Attorney Aaron Bortel is a dedicated advocate for those facing DUI charges in the Bay Area. Committed to helping clients avoid jail, save their driver’s licenses and jobs, and prevent permanent criminal records, he combines deep legal expertise with genuine care for his client's welfare. Trust in a lawyer who not only defends but truly supports you through challenging times.

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