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Are Breathalyzer Tests Always Accurate?

Are Breathalyzer Tests Always Accurate?

When an officer suspects a driver is intoxicated, they need probable cause to believe they were driving under the influence (DUI) in order to make an arrest. A common way officers try to obtain probable cause is by conducting a breath test using a device known as a Breathalyzer. If the Breathalyzer indicates a driver has a blood alcohol content (BAC) of 0.08 percent or higher, the officer can automatically use that reading as probable cause for an arrest. In addition, the prosecutor can use the Breathalyzer results to prove that a driver was intoxicated, as 0.08 is the legal limit for DUI per se.

Considering the importance of the Breathalyzer results in many DUI cases, you would imagine that the devices should always be accurate and reliable, right? Unfortunately, that is not the case, as there are many factors that can cause an inaccurate Breathalyzer result and, in many cases, a wrongful conviction if the prosecutor uses the inaccurate reading as evidence in a criminal case. It is critical to have a DUI defense lawyer who knows how to challenge Breathalyzer results when appropriate.

Reasons for Breathalyzer Errors

While there are different types of Breathalyzer devices, all of them have the potential for errors. In fact, the more portable devices that police officers use at roadside stops have a higher chance for errors than the more reliable devices kept at the police station. The following are some reasons why a Breathalyzer reading would be inaccurate.

Margin of Error

Like most scientific tests, Breathalyzers have an inherent margin of error. This means that even in the ideal circumstances, the result of the breath test still might not be perfectly right. Many Breathalyzer devices have a margin of error of 0.01 percentage points. This means that if a reading is 0.08 percent on the nose, your true BAC could be anywhere between 0.07 percent and 0.09 percent. Authorities should always consider this margin of error when using evidence of a breath test reading in a DUI case.

Inadequate Calibration

Breathalyzer devices require regular calibration. This is usually done by a police lab technician who runs a particular solution with a certain concentration of alcohol through the device. They then tune the device to match the exact concentration of the solution. Some states require that officers calibrate the devices at certain intervals, such as every 150 uses or every 10 days. Other states do not have specific requirements. If a police department fails to properly calibrate devices—or even calibrate them at all—highly inaccurate readings can result.

A Suspect’s Mouth Alcohol

A Breathalyzer measures the alcohol vapor from your lungs, also known as mouth alcohol. In some situations, alcohol from your stomach or that is lingering in your mouth can accidentally be measured by the device. This is especially true if someone vomits or burps a short time before being tested. The mouth alcohol has not yet been introduced into the bloodstream and has not had intoxicating effects on the driver, so it can artificially increase the BAC reading.

Some Breathalyzers are designed to account for mouth alcohol with a slope reading. If there is mouth alcohol, the reading will spike for a period of time and then will decrease to the accurate breath alcohol level. However, not every device will adjust its reading to avoid mouth alcohol measurements. Instead, police officers are expected to wait and observe a driver for about 15 or 20 minutes before administering the test. This is called the deprivation period, which should rid the driver of any mouth alcohol. The officer should closely observe the driver to make sure they do not vomit, burp, or put anything else in their mouth during this time. If an officer fails to wait for the deprivation period, there is a definite chance of an inaccurately high reading due to mouth alcohol.

Contaminated Breath Samples

For a completely accurate result, the Breathalyzer should only measure the driver’s breath sample. However, fumes or vapors in the atmosphere or even the mouth alcohol of the person who previously submitted a sample into the device may taint the sample. Police officers should always replace the mouthpiece of the Breathalyzer between tests—both for accuracy and sanitation purposes. They should also shoot something called an air blank through the tube of the device to clear out any fumes or vapors that may be lingering in the sample chamber.

Interference by Radio Frequency

Another factor that can affect the accuracy of a Breathalyzer is radio frequency interference, or RFI. A police radio can emit electromagnetic waves, which can cause malfunctions in the Breathalyzer. Some devices have RFI detectors, and will cancel tests that are in progress in the presence of interference. Again, not all Breathalyzers are so equipped, and RFI can lead to false results and wrongful convictions.

Overall, Breathalyzer devices are not infallible. When police officers and prosecutors rely solely on a Breathalyzer reading over 0.08 percent, people can face a wrongful conviction if they do not mount a proper defense. The right defense attorney should investigate to determine whether any factors made the breath test results unreliable. By successfully calling those test results into question, the prosecutor will need to present other evidence to prove DUI charges beyond a reasonable doubt.

A DUI conviction can be more serious than you may think, as there will be many lingering consequences in addition to probation, a license suspension, fines, and other court-imposed penalties. Having qualified defense representation is key to protect your rights and obtain the best possible outcome in your case.

Contact a DuPage, Kane, and Cook County DUI Defense Law Firm Right Away

The criminal defense attorneys at Martin & Kent, L.L.C., represent defendants in DuPage, Kane, and Cook Counties who face a variety of criminal charges, including DUI. We will identify all possible defense in your specific case, so please call (630) 474-8000 as soon as possible.



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