Earlier this month, Houston police received a concerned call about a potentially drunk driver at a local fast food restaurant. The caller noted that the driver had been sitting at the restaurant's drive-through window for more than 20 minutes. While responding to the call, an officer witnessed a vehicle without a license plate driving without its lights on. The officer diverted from the original call and proceeded to pull over the driver of this vehicle. According to reports, the vehicle smelled like alcohol and the driver was uncooperative. Subsequent chemical tests determined that her blood alcohol concentration was nearly three times the legal limit. She was arrested and charged with her second DWI offense.
How Reliable Are Breath Tests?
Police actually tested the DWI suspect's breath twice. While both tests showed that she was intoxicated, the results were not identical. The first test showed a blood alcohol concentration of .227 percent. The second test showed a blood alcohol concentration of .218 percent. That's a difference of nearly one-tenth of one percent. It may not sound like much, particularly in this context where the BAC is so extremely elevated, but an additional .009 percent could be quite significant in other DWI cases.
Why would the police execute a breath test twice? Which test results should be used in a criminal case? What could cause the results to vary? These are all important questions.
Multiple Tests: Police officers may perform more than one breath test if the results of a first test are surprising or questionable. In this case, the driver's first breathalyzer result was .227 percent. That's nearly three times the legal limit of .08 percent. A second test can help to either (a) confirm the first test's accuracy or (b) secure a correct result.
Using the Results: In situations like the one at hand, officers may not have to rely on one test over another. The driver's blood alcohol concentration consistently tested well above the legal limit. In other cases, however, one test may show that a driver's BAC is .082 percent, while another test shows a BAC of .073 percent. That's a difference of .009 percent. One puts the driver over the legal limit, the other does not. Which test is most reliable? The state will want to use the first test (.082 percent) as evidence to support a DWI arrest. The driver, on the other hand, will want to use the second test (.073 percent). The driver's attorney will have the responsibility of casting doubt as to the reliability of the first test.
Varying Results: There are many reasons why breath test results may differ. These include:
- The amount of time that has lapsed between breath tests
- The amount of alcohol consumed by the driver
- Food consumed by the driver
- Errors in performing the test; and
- Performing the first test with deep lung air while using shallow breath for subsequent tests.
The fact that test results are varied can help your DWI case. The greater the difference in the results, the better. Your attorney can use this to undermine the validity and reliability of those tests. This can help you secure the best possible result.
Contact the Doug Murphy Law Firm, P.C. if you are facing criminal DWI charges in Houston. Our experienced DWI defense lawyers will review your case and help you understand your legal rights. Call today to learn more.