Breath tests can feel definitive—“the machine says .10, so I’m done.” But in real DUI litigation, breath results are often challenged because a breath device is not measuring your blood directly. It is estimating BAC using assumptions about how breath relates to blood alcohol, relying on proper procedures, instrument accuracy checks, and the conditions under which the sample was collected. When any of those pieces are weak, the number becomes less persuasive—and sometimes the way the test was handled becomes a central defense issue.
California also has forensic alcohol testing procedures (often called “Title 17” rules) that set baseline standards for how breath alcohol testing should be performed, including requirements for duplicate samples and periodic accuracy determinations. Breath cases often turn on whether those standards were followed and whether the records actually support the reliability of the result.
How Breath Tests Are Supposed to Work (Alveolar Breath Basics)
Breath testing is built on the idea that deep-lung breath—often described as alveolar breath—reflects alcohol in the blood near the lungs. California’s forensic alcohol regulations define alveolar breath as expired breath in equilibrium with alcohol in adjacent pulmonary blood, and the breath collection rules describe the sample as expired breath that is essentially alveolar in composition.
In plain English, the test is trying to capture deep-lung breath, not “mouth air.” If the sample is not truly alveolar—or if it is contaminated—the result can be questioned. This is why breath testing procedures focus so heavily on observation rules and contamination risks before a sample is collected.
This page and website provide general information in plain English, not legal advice. Laws and local court/DMV practices vary and can change, so don’t rely on this content for your case—talk to a qualified attorney promptly to review your specific facts, especially if you face charges, a DMV action, or a deadline. In many cases, you’re fighting two battles at once: the DMV process and the criminal court case.
The 15-Minute Observation Period and “Mouth Alcohol”
California’s breath collection rules state that a breath sample should be collected only after the subject has been under continuous observation for at least fifteen minutes before collection, and during that period the person must not ingest fluids or alcohol, regurgitate, vomit, eat, or smoke. That rule exists because “mouth alcohol” can artificially inflate breath readings. Residual alcohol can remain in the mouth after drinking, and the purpose of the observation window is to reduce the chance that a reading reflects contamination instead of deep-lung breath.
When the observation period was not truly continuous—or when there is evidence of burping, regurgitation, vomiting, eating, smoking, coughing, or other contamination risks—breath results can be attacked as unreliable. In many cases, the defense focus becomes simple: the protocol exists for a reason, and the state has to show it was actually followed.
Title 17 Rules That Matter Most in Breath Test Cases
When people say “Title 17 violation,” they usually mean the baseline standards weren’t followed, so the result is less reliable and less persuasive. In many cases, the dispute is not about whether the officer wrote “Title 17 compliant” in a report—it’s whether the underlying records and video support compliance.
A major Title 17 safeguard is the duplicate sample rule. Title 17 standards require analysis of two separate breath samples that do not differ from each other by more than 0.02 grams per 210 liters of breath. That’s a built-in reliability check. When the two samples are far apart, it raises a red flag that the testing environment, sampling method, device performance, or contamination risks may have affected the result.
Title 17 also requires periodic accuracy determinations. The regulations define “periodic” to mean either a period not exceeding 10 days or following testing of every 150 subjects, whichever comes sooner. In plain English, the device is supposed to be checked on a schedule, and the paper trail matters. When accuracy documentation is missing, late, sloppy, or inconsistent, it becomes a credibility problem for the number.
Calibration, Accuracy Checks, and Maintenance Problems
Even if a test is administered “correctly,” the instrument still has to be functioning correctly. Breath testing devices depend on maintenance, control checks, accuracy determinations, and records that show the machine was operating within acceptable limits around the time of the test. When the records are incomplete or reveal repeated out-of-tolerance readings, the defense can argue the number is not trustworthy.
Maintenance issues aren’t technical trivia. In real cases, calibration history, accuracy check logs, and maintenance records often determine how persuasive a breath result is—especially when the result is near the legal limit or when the officer’s impairment narrative is weak.
Operator Error: How the Test Can Be Administered Wrong
Breath tests are not fully automatic “truth machines.” Operator choices and real-world conditions can affect outcomes. A test can be undermined by a weak or non-continuous observation period, rushed or unclear instructions that lead to an inadequate breath sample, interruptions or repeated attempts that are not properly documented, and failures to recognize contamination risks like coughing, regurgitation, smoking, or eating. Even the duplicate sample safeguard becomes an issue if the testing process does not produce compliant samples that agree within the required range.
When the prosecution wants the jury to treat the number as definitive, the defense response is to show the process was human-driven, protocol-driven, and record-driven—and that failures in any of those areas reduce reliability.
Medical Conditions and Substances That Can Skew Results
Some breath-test disputes involve medical or physiological issues that can complicate interpretation. The safest and most accurate way to frame this is not “this condition proves the result is false,” but rather that certain conditions can create contamination risks or raise legitimate questions about the reliability of a breath reading in a particular case.
For example, because the regulations treat regurgitation and vomiting as contamination concerns during the pre-test period, reflux-like events can become important—especially if there is video, officer notes, or a timeline suggesting burping, coughing, or regurgitation around testing. In other situations, certain metabolic states can produce breath compounds that may complicate interpretation depending on the device technology, which is why medical records and expert review can matter when a case is contested.
Breath testing also isn’t only affected by drinking itself. The broader scientific point is that residual alcohol in the mouth can elevate readings, which is one reason protocols emphasize the observation period and contamination controls.
When Timing Matters: Arrest, Testing, and BAC Changes
Breath tests are taken after driving ends, and the gap between driving and testing can matter because BAC can rise or fall over time. If alcohol absorption was still occurring, BAC at the time of testing can differ from BAC at the time of driving. That timing issue becomes especially important when prosecutors lean heavily on a single number without proving how it reliably connects back to the driving time.
How a DUI Lawyer Challenges Breath Test Results
A strong breath-test defense is evidence-driven, not just argumentative. It typically begins with demanding the full breath-testing packet, including printouts of all breath samples, timestamps, operator identification, observation documentation, and instrument records. From there, the defense usually triages the core compliance issues: whether there was a compliant 15-minute observation period, whether two samples were collected and agree within the required range, and whether the device has documented periodic accuracy determinations consistent with the regulatory framework.
Video review is often decisive. If an officer claims continuous observation, but bodycam shows distractions, breaks in supervision, or contamination risks, that becomes a credibility problem tied directly to the rule. In contested cases, the defense may also use an expert to evaluate sampling issues, instrument performance, contamination risks, and whether the state’s interpretation is scientifically and procedurally sound.
FAQs About VC 23152(g)
Can a DUI blood test be wrong in California?
Yes. A blood result depends on proper collection, preservation, chain of custody, and lab analysis. Title 17 requires handling that maintains identity and integrity, and it sets specific collection rules.
Is it a problem if the nurse used an alcohol swab?
It can be a major issue because Title 17 says alcohol or other volatile organic disinfectant shall not be used on the skin where blood is collected.
Do DUI blood tubes have preservatives?
They are supposed to. Title 17 requires mixing blood with an anticoagulant and a preservative.
DOJ BFS describes grey-stopper tubes containing potassium oxalate and sodium fluoride, and notes other containers may be vulnerable to legal challenge.
Can I get my blood retested?
Title 17 states the remaining portion of the sample shall be retained for one year to allow analysis by the defendant.
Whether a retest is possible depends on whether the sample still exists, was stored properly, and is available through lawful discovery procedures.
What is “chain of custody” and why does it matter?
It’s the documented history of who handled the evidence and when. Title 17 requires maintaining identity and integrity throughout the process.
DOJ BFS guidance emphasizes labeling, sealing, and chain-of-possession signatures for everyone handling the sealed evidence envelope.