Questioning the validity of the breath test in Minnesota

When law enforcement officers stop drivers for suspicion of operating a vehicle while intoxicated, they routinely administer field sobriety and breathalyzer tests to determine the extent of the drivers’ inebriation.  The same often occurs when officers perform routine traffic stops and believe they have reason to suspect that drivers are under the influence of alcohol. However, while the use of breathalyzers is routine and generally accepted, their validity and accuracy has come into question.

How breathalyzers operate

Contrary to popular belief, breath tests don’t directly determine blood alcohol concentration. Breathalyzer machines measure the amount of ethanol present in a sample of air.  When individuals breathe into the mouthpiece, any ethanol that is present in the sample, whether from alcohol or outside substances, is converted to acetic acid and water, and the machine measures the electrical current that the chemical reaction produces. It then takes this information and indirectly estimates BAC using varying technologies and complex calculations.

The National Motorists Association reports that studies have shown a margin of error as high as 50 percent when comparing actual blood alcohol concentration and breathalyzer estimates. With that figure, anyone who receives an estimate of 0.1 percent BAC could have an actual BAC of anywhere from 0.05 percent and 0.15 percent.

Factors that affect accuracy of the test

Many factors can affect breathalyzer accuracy, leading to such a wide gap between estimates and real BAC.  When the machines take their measurement, they measure not just the ethanol in the breath sample, but all of the other molecules that are structurally similar to ethanol within that sample as well. Common interfering substances include:

  • mouthwash
  • gasoline additives
  • workplace compounds, such as lacquer, paint remover and cleaning fluids
  • Increased acetone levels due to dieting or diabetes 

Blood cell volume settings on the breathalyzers themselves may also contribute to inaccurate results.  Most machines have a standard hematocrit setting of 47 percent, yet that number varies from 42 to 52 percent for men and from 37 to 47 percent for women. Those at the lower end of the spectrum can face false positive results. Improper calibration and use by authorities also contributes to inaccuracies.

Within the legal process

A Pennsylvania judge deemed breathalyzer test results inadmissible in his December 2012 opinion when asked to review the methods by which a breath test machine is calibrated.  His opinion questioned the accuracy of the test results, indicating that outcomes for very high and very low levels of intoxication were the most severely affected.  South Dakota has gone so far as to prohibit the use of breathalyzers of any kind.

Despite the questionable accuracy of breathalyzers and their proven issues, they continue to be used by law enforcement across the nation. Minnesota residents should remember that only a blood test can unequivocally determine the actual amount of alcohol in the blood.

Max Keller has won countless jury trial cases involving misdemeanors and felonies, sex crimes, and DWI’s. He is a member of the Minnesota Society for Criminal Justice, which only allows the top 50 criminal defense attorneys in the state as members. Max is a frequent speaker at CLE’s and is often asked for advice by other defense attorneys across Minnesota.

Years of Experience: Approx. 20 years
Minnesota Registration Status: Active
Bar & Court Admissions: State of Minnesota Minnesota State Court Minnesota Federal Court 8th Circuit Federal Court of Appeals State of Maryland

What to Do If You Have Been Charged with a Criminal Offense

The timeline for filing pre-trial motions in a criminal case in Minnesota varies with the type of motion. A motion related to the discovery of evidence or dismissal of a criminal case must be filed at least three days before the Omnibus Hearing. The prosecution is then allowed to respond to the motions, and the court sets the timeline for these responses.
Knowing the tips for interacting with law enforcement as a suspect in Minnesota can keep you from saying or doing something that incriminates you. These tips include understanding your rights while interacting with law enforcement, knowing how to handle search and seizure, and seeking the early intervention of a criminal defense lawyer. You should apply these tips when you are stopped for questioning, a suspect in a criminal investigation, pulled over in a car, and during arrest, arrest processing, and custody.
You may need to hire a criminal defense lawyer even if you have not been charged. A criminal defense lawyer protects your rights when law enforcement officers are investigating you for a crime. Without a lawyer, you might say something that could be incriminating or misconstrued. Your lawyer can engage with the police or the prosecutors and provide evidence that prevents them from filing formal charges. Your lawyer can also go through your case and prepare a defense strategy if there is a possibility of you getting charged.