Unreliable breath test results may lead to DUI conviction errors

Although law enforcement uses breath test devices to determine drivers’ blood alcohol level, the results from these devices may be inaccurate.

People who drink and drive in Chicago run the risk of getting pulled over by Illinois law enforcement. In some cases, officers will use a breath test device to determine whether the driver is intoxicated. The legal limit in Illinois is 0.08 percent, and drivers who have a blood alcohol content level over that amount may be charged with a DUI. Yet, many studies show that breath test devices yield inaccurate and unreliable results. These inaccurate breath test readings may be used as scientific evidence in court to convict people of drunk driving. Yet erroneous breath test results may cause the wrongful conviction of innocent people in Illinois and across the country.

The inner workings of a breath test device

Instead of measuring a person's blood alcohol content level through a blood sample, a breath test device detects how much alcohol is present in a person's breath sample. The driver is instructed to submit a breath sample through a tube that is connected to the device. The machine then analyzes the breath sample for the presence of ethyl alcohol and converts that amount into a blood alcohol content level. Thus, the driver's BAC is determined without actually measuring the blood at all. This method of obtaining a BAC has proven to be inaccurate in many cases.

Research performed at the State University of New York at Potsdam compared the results of a BAC obtained from a blood test to the BAC calculated from a breath test device. Experts found that at least 23 percent of the time, the BAC reading from the breath test was significantly higher than the results obtained from the blood test. In some cases, the two readings varied by as much as 15 percent. This seemingly small variability may result in a DUI conviction error.

Factors that affect breath test device readings

Researchers from the State University of New York at Potsdam have also found several things that can affect the accuracy of a breath test reading. These include:

  • The presence of tobacco smoke, moisture and dirt in the air
  • Electrical interference from cellphones and officer radio devices
  • Any residual vomit, blood or certain types of food left in the driver's mouth
  • Whether the driver inhaled any paint, paint thinner or gasoline fumes prior to testing
  • Whether the breath test device has been calibrated properly to reflect the surrounding air temperature and humidity level

Studies show that officers who do not use the breath test device correctly can obtain inaccurate results as well. According to the Illinois Administrative Code, officers must be properly trained on how to use breath test devices. The code also gives specific requirements for maintaining breath test equipment.

How an attorney can help

A DUI conviction can impact many areas of a person's life. Not only can a DUI make it difficult to obtain a professional license or financial assistance, but it can cause problems when seeking employment in certain industries. In order to avoid a wrongful DUI conviction, people charged with a DUI may want to contact a criminal defense attorney. A lawyer may be helpful in creating a strong defense case to fight a DUI in Illinois.

Keywords: Unreliable breath test, DUI , conviction , BAC , Illinois law enforcement