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The Science of Breathalyzers: Limitations and How They Work

By San Diego Attorney on December 4, 2023

California has strict DUI laws to prevent people from driving while intoxicated. Drivers face harsh penalties when convicted of a DUI that may include a revoked or suspended license, heavy fines, and jail time.

There’s a lot on the line when someone is accused of DUI, including the driver’s freedom, reputation, and ability to earn a living. That’s why it’s so important that we maintain a fair and accurate process for determining if a driver is legally intoxicated. Unfortunately, due to technological limitations and the possibility of human error, the breathalyzer tests used to determine the blood alcohol content (BAC) of California drivers lack credibility.

If you have been charged with a DUI based on breathalyzer test results, speak with an experienced San Diego DUI lawyer right away. Your attorney will inform you of your rights and find the best legal strategy to protect your driving privileges.

The Limitations of Breathalyzer Tests

A breathalyzer is a device that uses infrared light to calculate a driver’s BAC by collecting a sample of their breath. A driver suspected of driving under the influence may be asked to take a roadside breathalyzer test, known as a preliminary alcohol screening (PAS). Drivers 21 and older and not on DUI probation are not required to take a roadside PAS, but drivers under 21 or on DUI probation face mandatory license suspension if they refuse to take a roadside PAS. There is no benefit in taking a roadside DUI test if you are not legally required to do so.

After a driver is arrested for suspected DUI, they will be given a choice of taking either a blood test or a breathalyzer test to determine BAC. At this point, a DUI suspect cannot refuse to take a BAC test without facing serious consequences that may include jail time and a yearlong suspension of their driver’s license. A post-arrest BAC is referred to as an evidentiary test, and these results are considered legal evidence of intoxication.

Breathalyzer tests have serious limitations, and your San Diego DUI defense attorney may be able to challenge their validity if you have been charged with DUI. One of the biggest problems with breathalyzer tests is that they don’t actually measure the amount of alcohol in the driver’s system.

A breathalyzer doesn’t test for the presence of ethanol, which is the chemical that causes people to become intoxicated. Instead, the infrared light in the breathalyzer is designed to detect the presence of methyl group chemicals, which are part of the ethanol molecule. The problem with this approach is that there are several chemical compounds found in human breath that may contain methyl group chemicals.

Due to a  breathalyzer’s inability to differentiate non-alcohol-based methyl compounds from ethanol, there are many factors that may inaccurately elevate the driver’s BAC reading. Another issue that may reduce a breathalyzer’s reliability is when the person taking the test is unable to inhale deeply enough to provide a reliable sample of air from their lungs.

Factors that may reduce the accuracy of breathalyzers include:

  • Diabetes
  • Fasting
  • A keto diet
  • Smoking
  • GERD
  • Mouthwash
  • Metabolism
  • Weight
  • Breathing issues
  • Eating bread products

Malfunctioning Breathalyzers and Human Error

In addition to the limitations caused by the way breathalyzers are designed, technological issues and the possibility of human error also call into question the reliability of breathalyzer tests. These machines must be serviced and recalibrated on a regular basis to work as intended. Another problem is that the people who operate breathalyzers at police stations may not have the necessary training and experience to use the machines correctly.

The following issues reduce the reliability of breathalyzers:

  • Improper calibration
  • Broken machines
  • Inadequate programming
  • Failure to follow protocols
  • Poorly trained operators
  • Failure to maintain accurate testing records

Were You Arrested for DUI in San Diego?

James N. Dicks of jD Law Criminal Defense Attorneys has 30 years of criminal justice experience. He’s deeply familiar with the courts, judges, and prosecutors of San Diego and how they operate. If you’ve been charged with DUI, we will pursue every strategy to get the charges against you dismissed or reduced.

Our firm has been recognized for providing clients with superior service by the esteemed rating agency Super Lawyers.

Call (760) 630-2000 to schedule a FREE consultation today. We are available 24/7 and speak English and Spanish.

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