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The Unreliability of the Breath Test

The breath test is the most common test that people are asked to take once they are taken to the police station, but it is also highly susceptible to error. If the test is not taken just right, then it will not accurately measure your blood alcohol concentration and your lawyer may be able to persuade the judge to throw it out. The main reason for the test’s potential inaccuracy is that, while it is supposed to measure how much alcohol is in your lungs, any residual alcohol in the mouth will result in a mistakenly high reading. Below is a list of additional factors that can make a breath test unreliable.

The Temperature of Your Breath
The breath test works on the assumption that your breath is 34 degrees centigrade. Studies done with this equipment have shown that the real average breath temperature for people who have been arrested on a DUI/DWI is closer to 35.5, with some as high as 37. This alone would mean that the result of the test would be between 10 and 20 percent higher than it really is.

How Fast Your Body Eliminates the Alcohol
Everyone has a different metabolism, but the breath test assumes that everyone is the same. This means that a person whose body gets rid of alcohol slower will have a higher BAC than someone with a faster metabolism, even after having the same amount to drink. Breath testing assumes that the person is “post absorptive.” This means that the test assumes that the person is no longer absorbing alcohol into the blood. If you have a slow metabolism, you might still be absorbing alcohol by the time you take the test. If so, it will read your BAC as significantly higher than it actually is. If you know or suspect that you have a slower than average metabolism, you may eventually argue that your metabolism skewed the result of your test.

Belching, Hiccupping or Vomiting Prior to a Test
Time is the most important factor here. A person should not be tested for at least 15 minutes after belching, hiccupping or vomiting, as this increases the amount of alcohol on the breath. The officer is required to constantly observe you to ensure that you have not belched, hiccupped or vomited within 15 minutes of taking the test. Constant observation is a rule that the officer must follow. If it is not followed, the results of the test may be called into question.

Problems in Mouth, Such as Blood, or Dentures
If there is any blood in your mouth when you take the test, it may increase the BAC result. If you have dentures, which trap alcohol in the mouth, it may skew the test result.

Other Chemical Compounds in Your Mouth
Strictly speaking, the breath test does not detect alcohol (ethyl alcohol). It detects part of the alcohol molecule called the methyl group. The significance of this is that the breathalyzer will also register other compounds besides alcohol, other compounds that are commonly found in human breath. If any of these compounds are present, it will result in an inflated and inaccurate BAC reading.