How Do Breathalyzer Tests Work? Insights For Tennessee Drivers

Barnes & Fersten Law Firm

Barnes & Fersten Law Firm

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Officer using breathalyzer on woman in car

One of the primary tools used in DUI investigation is the breathalyzer, a device that measures alcohol levels in your breath to determine if you’re over the legal limit. Knowing how this device works and how it affects your rights on the road can make a big difference in how you approach driving after consuming alcohol.

In this guide, we’ll delve into the specifics of breathalyzers and their role in DUI enforcement in Tennessee. We’ll answer some common questions, including how breathalyzers work, how long a breathalyzer can detect alcohol in your system, and what happens if you refuse a breathalyzer.

How Does A Breathalyzer Work?

Breathalyzers are a key tool in the enforcement of DUI laws, enabling law enforcement officers to quickly assess a driver’s blood alcohol content (BAC). But how exactly does a breathalyzer work?

Breathalyzers operate on a simple principle: they measure the amount of alcohol in the air you exhale to estimate the concentration of alcohol in your blood. When you drink alcohol, it enters your bloodstream and is eventually metabolized by your liver. However, as your blood circulates through your lungs, some of the alcohol moves across the membranes of the lung’s air sacs (alveoli) into your breath, which can then be measured.

There are several types of breathalyzers, but most used by Tennessee law enforcement work through fuel cell technology and infrared spectrometry. Fuel cell breathalyzers measure the chemical reaction of alcohol with a fuel cell, producing an electrical current proportional to the amount of alcohol detected. Infrared spectrometry breathalyzers, on the other hand, use infrared light to detect the unique molecular structure of alcohol in your breath. Both methods provide quick and reasonably accurate BAC readings under perfect conditions, but there are still many defenses to breathalyzer tests.

Various factors, including the device’s calibration, the method of administration, and even the driver’s physical condition, can affect the accuracy of a breathalyzer test. In Tennessee, the legal limit for most drivers is a BAC of 0.08%. Reaching or exceeding this threshold can lead to DUI charges, with significant legal and personal consequences.

How Long Does Alcohol Stay In Your System?

Once alcohol is consumed, it is rapidly absorbed from the stomach and intestines into the bloodstream, bypassing the normal digestion process. The liver then becomes the central processing unit, metabolizing the alcohol at a steady rate. However, this rate can vary widely among individuals, influenced by factors such as body weight, gender, the rate of alcohol consumption, and the presence of food in the stomach.

The question of how long alcohol stays in your system and remains detectable by a breathalyzer hinges on individual metabolic rates. Generally, alcohol is metabolized at a rate of about 0.015% BAC per hour, but this can vary. This explains why the effects of alcohol—and its detectability—can last several hours after drinking. For instance, the alcohol from two beers could take over three hours to fully metabolize and no longer be detectable by a breathalyzer for most individuals.

It’s important to remember that the safest approach to driving is not to attempt to calculate your own BAC or its decline over time, but to avoid driving altogether after consuming alcohol. This approach ensures not only your safety but also that of others on the road. Understanding the metabolism of alcohol can help you make informed decisions, but it should not be used to estimate one’s ability to drive legally or safely after drinking.

Does A Breathalyzer Detect Weed Or Other Drugs?

Breathalyzers are fundamentally designed to detect alcohol—specifically, ethanol, the type of alcohol found in beverages. Given this specific calibration, standard breathalyzers do not detect other substances, such as THC from marijuana and hemp products. As such, if officers suspect marijuana impairment they should be requesting a blood draw. Otherwise, officers will have a tough time arguing that you were impaired of marijuana if they only get breath and your BAC comes back below a .08.

It’s worth noting that a DUI charge is not limited to alcohol consumption–any intoxicating substance that impacts one’s ability to drive could result in a DUI, including prescription medication. In Tennessee, if impairment by substances other than alcohol is suspected, law enforcement officers may resort to alternative methods to discern intoxication levels. These can include field sobriety tests and chemical tests (such as blood or urine tests), which can detect a broader array of substances, including marijuana, mushrooms, cocaine, and opioids.

What Happens If You Refuse A Breathalyzer?

In Tennessee, making the decision to submit to a breathalyzer test during a DUI stop involves understanding the state’s implied consent laws and the potential ramifications of your choice. The question of whether you can refuse a breathalyzer is more than a simple yes or no—it’s a decision that carries significant legal and practical consequences.

Tennessee’s Implied Consent Law

Tennessee operates under implied consent laws, which means that by driving on public roads in Tennessee, drivers have automatically agreed to submit to breathalyzer tests if lawfully requested by a police officer. Refusing a breathalyzer test or similar chemical tests will likely result in an implied consent charge. However, it is important to note that providing a breathalyzer sample with a BAC above a .08 likely will increase the risk of conviction of a DUI that requires the same loss of license but with substantially greater penalties in addition to the loss of license such as jail, fines and probation.

Understanding Your Rights And Protections

It is important to remember that an officer must have probable cause to request a breathalyzer test and must inform you of the consequences of refusal. The police officer doesn’t have to detail the exact suspension length but must clearly state that refusal can lead to license suspension. However, a DUI conviction carries harsher penalties, including jail time and license suspension. Consenting to a breathalyzer provides law enforcement with concrete evidence of your BAC, which can be critical in prosecuting a DUI case. 

Many Tennessee drivers are unaware that refusing a breathalyzer doesn’t automatically result in license loss. If you’re charged with implied consent, you’re entitled to a hearing where the state must prove the officer had probable cause and that you were properly informed of the test refusal consequences. There are legal nuances and defenses that a Knoxville DUI attorney can leverage to potentially dismiss the implied consent charge. Knowing these facts and having experienced legal representation can make all the difference in how your DUI case is resolved.

Can I Beat A DUI If I Gave A Breath Sample Above A .08?

Maybe. Hiring a skilled DUI lawyer increases your chances at beating a DUI despite having a breathalyzer sample above a .08. At Barnes & Fersten we routinely get DUI’s above a .08 reduced or dismissed through countless legal issues impacting the reliability and/or admissibility of the breath sample. For example, an officer’s failure to observe you for 20 minutes before the breathalyzer can make the breath sample inadmissible. This is because you may have mouth alcohol, or alcohol in your mouth that impacts the validity and reliability of a breath sample. There are countless studies and examples showing an individual can take 1 shot of liquor and “gargle” it in their mouth then immediately take a breathalyzer with a result well above .08. Yet, that person clearly is not impaired and the true level of alcohol in their blood is well below a .08.

Similarly, breath samples through the implied consent law requires a signature prior to the breath sample, not after the breath sample. Yet, we routinely see officers fail to get a signature prior to the breath sample.

Medical conditions may impact the reliability of a breath sample as well. For example, an individual with GERD or acid reflux should be given a blood test, rather than breath, because it very likely will impact the sample by having breath alcohol.

There are countless other legal defenses to breath tests that our lawyers routinely argue in court for dismissals or reductions through negotiations.

Need A Knoxville DUI Defense Attorney? Call Barnes & Fersten

If you or a loved one is facing DUI charges in Knoxville or the surrounding areas, reach out to Barnes & Fersten today. Our attorneys have a proven track record in defending DUI cases, including challenging breathalyzer results. We’ll explore all available legal avenues, leveraging our expertise to strive for the best possible outcome in your case. Let our team provide the clarity and legal assistance you need to face Tennessee DUI charges with confidence. Contact us for a free consultation and take the first step towards reclaiming your future.

Attorney At Law, Managing Partner

Brandon D. Fersten is an esteemed Knoxville attorney practicing DUIcriminal defense, and juvenile law. Known for his empathetic approach and commitment to his clients, he brings a record of favorable case outcomes including dismissals and not guilty verdicts at jury trials resulting in Brandon being recognized as one of the “Top 40 Under 40” in Criminal Defense, U.S. News’ Best Lawyers: “Ones to Watch,” and Super Lawyers’ “Rising Stars”. Brandon’s professional accolades, combined with his passion for justice, position him as a reliable criminal defense advocate in the East Tennessee legal landscape.