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Can a Delayed Breath Test Render the Evidence Invalid?

June 28, 2016 • DUI Defense

When someone is pulled over because of suspected drunk driving, police generally want to administer a blood alcohol content (BAC) test. The purpose of the test is to obtain evidence showing that a defendant's BAC is above the legal limit of .08. 

In one recent case reported on by The Washington Times, a BAC test was administered to a defendant, but not until two hours after he had first been pulled over. This was a problem because the body metabolizes alcohol and a person's BAC declines over time.

In order to address the fact that a delay in testing can make the driver's BAC lower at the time of the test than at the time he was driving, the crime lab in the case applied a scientific formula. A benchmark rate was used to determine what the defendant's BAC would have been at the time he was driving based on what it was when his test was actually administered.

The judge, however, held that the forensic laboratory's standards for calculating BAC were too inexact to meet the burden of proof required of prosecutors in court.  While this case was just one decision of a state court in Vermont and doesn't apply to higher courts or courts in other jurisdictions, it is an important decision because it could help other defendants structure arguments that call test results into question.

If the test is not scientific enough to be used, defendants can argue either that it should not be admitted or that the jury should not consider the evidence from the test to be strong enough evidence to prove guilt beyond a reasonable doubt.

A Tallahassee drunk driving lawyer can help defendants in drunk driving cases to identify many different ways to try to undermine the prosecutor's evidence. Making an argument about the inexact nature of a BAC test may be one of the possible arguments some defendants may wish to make.

Why a Delayed Breath Test May Not Be Valid Evidence

The lab in this particular case assumed that a person's BAC peaks 30 minutes after the last drink and that a person's BAC drops at a rate of .015 per hour after consuming the last drink.  Based on this formula, someone who took a BAC test two hours after he stopped driving and had a BAC of .05 would be assumed to have been at .08 at the time he was actually driving.

The problem is, people's bodies can metabolize alcohol at different rates. Even a senior forensic chemist at the state lab where the test was conducted acknowledged in her testimony that not only can there be a difference among different people at the rate their body processes alcohol, but there could also be a difference among the same person on different dates.

With so much potential variation, the formula is far too inexact to apply as evidence that could result in a criminal conviction.

Challenging the science behind a BAC test could be useful for defendants, especially as one judge has now found problems with this type of forensic formula -- other judges may also find credence in the same type of argument.

A drunk driving attorney in Tallahassee can help defendants who are accused of impaired driving identify the different ways they can try to undermine the case against them so a prosecutor cannot meet the burden of proof.