Breath test results are often presented in DUI cases as precise scientific evidence. In reality, breath testing relies on assumptions about human physiology, strict procedures, and properly functioning equipment. When any of those elements break down, the accuracy of the result can be questioned. Understanding how breath tests work and where weaknesses can arise is often a key part of building a DUI defense.
Mouth Alcohol and Residual Ethanol Contamination
Breath testing is designed to measure alcohol from deep lung air, which is believed to closely reflect alcohol levels in the bloodstream. Problems arise when alcohol vapor remains in the mouth or upper airway. Known as mouth alcohol contamination, this can occur after a recent drink, from burping or vomiting, from acid reflux or GERD, or from products like mouthwash, breath spray, or certain chewing tobacco.
To reduce this risk, officers are typically required to observe a driver for a set period before administering an evidentiary breath test. During this time, the person should not eat, drink, smoke, or place anything in their mouth. In practice, this observation period is not always followed carefully. Officers may be completing paperwork, moving the person between areas, or handling other tasks, which can interrupt the required monitoring. When observation procedures are not followed properly, the reliability of the breath result may be challenged.
Partition Ratio Variability and Breath Temperature
Breath-testing devices measure alcohol in exhaled breath and convert the value to an estimated blood alcohol concentration using a standard ratio. The common assumption is that blood alcohol is about 2100 times higher than breath alcohol. However, human physiology varies widely. Lung capacity, breathing patterns, and how alcohol is absorbed or eliminated can affect this ratio.
Breath temperature can also influence readings. Warmer breath carries more alcohol vapor, meaning factors such as fever, physical exertion, anxiety, or certain health conditions may increase a measured breath alcohol value. These physiological differences can become especially important when a breath test result is close to the legal limit.
Environmental and Chemical Interference
Breath testing devices are designed to detect ethanol, but they may also react to other substances under certain conditions. Exposure to volatile chemicals, solvents, or heavy use of alcohol-based products in a testing area can affect readings. Medical conditions that alter breath chemistry may also play a role in certain cases.
These situations do not automatically invalidate a breath test, but they can raise questions about whether the test environment and conditions were appropriate. When such issues are supported by documentation or video evidence, they can become part of a defense strategy.
Calibration, Maintenance, and Quality Control
The reliability of any breath testing device depends on proper calibration, routine verification checks, and detailed maintenance records. Law enforcement agencies must regularly confirm that breath instruments are functioning within acceptable limits.
Defense attorneys often review maintenance logs, repair records, and calibration documentation to identify patterns or gaps. Missing records, repeated adjustments, or inconsistent maintenance practices can undermine the reliability of a breath test result. Even when a device appears to have passed routine checks, incomplete documentation can raise doubts about whether the equipment was functioning properly at the time of testing.
Procedural Errors During Breath Testing
Breath tests must follow strict procedures to ensure accuracy. The observation period, sample collection method, and timing of multiple breath samples all play an important role. If a driver burps, coughs, vomits, or otherwise disrupts the observation period, testing protocols often require the process to restart.
Sample collection also depends on how the person blows into the device. Incomplete or irregular breath samples may produce inconsistent readings or require retesting. When breath samples do not closely match one another, it can signal problems with the collection technique, equipment stability, or contamination.
Legal Strategies for Challenging Breath Test Evidence
A strong DUI defense often involves closely examining both the science and the procedures behind a breath test result. Discovery requests may seek calibration records, maintenance logs, operator training documentation, body camera footage, and test data from the device itself.
Legal motions may challenge whether the state can prove the device was functioning properly, whether the operator followed required procedures, and whether the test conditions met regulatory standards. In some cases, cross-examination of officers or forensic witnesses reveals gaps in documentation or inconsistencies in how the test was administered.
When Breath Test Evidence Becomes the Focus of a DUI Case
Breath testing can play a central role in DUI prosecutions, but it is only one piece of the evidence. Driving behavior, field sobriety tests, body camera footage, and the timeline of events may all influence how the case is evaluated.
If you or a loved one is facing a DUI charge in Las Vegas and breath test results are a key part of the case, it may be important to have the evidence carefully reviewed. Goodman Law Group represents individuals facing DUI allegations and can evaluate the testing procedures, equipment records, and legal issues that may affect the reliability of breath test evidence. Early legal guidance can help identify potential weaknesses and determine the most effective defense strategy.