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Are BAC Chemical Tests Accurate?

The modern Breathalyzer looks like a very sophisticated machine. It is compact, sleek, user-friendly, and fast. When police lab technicians take the stand to talk about fuel cells and electrical impulse conversions, these machines sound even fancier. It's not fair to say that these gadgets are all sizzle and no substance. But, that assessment is not too far from accurate.

Blood tests are a little different. There may be no better measurement of a person's Blood Alcohol Content than examining a blood sample. However, blood tests also involve lots of variables and moving parts.

Breathalyzer Flaws

Breathalyzers do not measure BAC levels. They estimate BAC levels based on the breath alcohol content. Prosecutors usually skip over that extra step as they explain how Breathalyzers work.

Another oft-omitted fact is that today's Breathalyzer is not much different from the 1938 Drunk-o-meter. Back then, a device which estimated blood alcohol content by measuring ethanol particles in the breath was cutting-edge technology. Now, some eighty years later, not so much.

The combination of roundabout measurement and an aging technology sets the stage for some flaws that many jurors can wrap their heads around. Mouth alcohol is a good example.

Officers have to closely monitor defendants for at least fifteen minutes prior to Breathalyzer tests. Prosecutors, who perhaps do not understand the science behind the test, often consider this requirement cumbersome but it is required pursuant to the Texas Administrative Code. Today, the "monitoring period" may be overlooked but it is still required.

Afterwards, some prosecutors patted themselves on their backs, thinking they had closed a legal loophole. But this particular approach may have backfired.

With no closely watched monitoring period, there is no way to tell if the defendant burped, vomited, or belched prior to the test. Such acts release alcohol into the mouth. The mouth alcohol produces an artificially-high result.

Flaws like this one are especially important in borderline cases, like a .09 BAC. Prosecutors will reluctantly admit that the Breathalyzer has a margin of error. Once jurors understand how this contraption works and does not work, they are usually willing to enlarge the margin of error.

Blood Test Flaws

In this case, the problem is not so much with the test itself, but the procedures surrounding the test.

Usually, either undertrained police chemists or overworked lab technicians analyze these samples. If a top expert reviews the sample in a top-flight laboratory, the results are often different.

Chain of custody is sometimes an issue as well. Many times, the blood sample goes from a clinic to a police substation to a processing facility to the district attorney's office to the courthouse. Whew. That's a lot of movement. Gaps in the chain of custody do not invalidate the evidence. However, they do make the sample's authenticity questionable. Given the high burden of proof in these cases, that could be enough to create reasonable doubt as to intoxication.

BAC chemical tests are not 100 percent reliable. For a free consultation with an experienced criminal defense attorney in Weatherford, contact Herreth Law. Home and jail visits are available.

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