A standard threshold for determining whether a driver is too intoxicated to safely operate a vehicle in the United States is if their blood alcohol content level (BAC) is at .08 percent or higher.
While taking an individual's blood is the most reliable way to get an accurate read of a driver's BAC, it requires a driver to be taken to the hospital to do it.
Contrary to popular belief, Breathalyzer tests aren't generally performed in the field, but instead back at the police station. Oftentimes, if a breath test does occur in the field, then if involves the use of a portable breath test (PBT) device, which is different from a Breathalyzer.
Therefore, field sobriety tests are often what's relied upon to establish probable cause necessary to arrest someone for driving under the influence (DUI). In some jurisdictions, field sobriety testing occurs in conjunction with a use of the PBT. The results of the latter are seldom admissable in court.
When it comes to trying DUI cases in court, one of the reasons breath test results are often not admitted as evidence in cases is because they've been shown to be inherently unreliable. DUI defense attorneys are often quick to point this out.
They often produce false positive results due to poor calibration or dying batteries. In other instances, the software that the breath testing device may run on may develop bugs that cause it to produce inaccurate results.
If it's used around toxins like varnishes, paint fumes or chemicals that go into adhesives or plastics, then it can cause it to produce inaccurate results. Situations in which an individual has used an alcohol-based product, such as mouthwash, prior to the test being performed can skew results too.
An officer being improperly trained or careless in his or her use of the device may give way to a failed test result. This is oftentimes why it's recommended that the device be used several times during the course of a single stop if intoxication is suspected. Doing so will allow for results to be confirmed.
If you've been charged with drunk driving and you have reason to question the efficacy of your breath test results, then a Christiansburg DUI defense attorney can advise you of your rights in your case.