The Science Behind Breathalyzer Devices — Can They Be Wrong?

How California breath testing works (the short course)

California uses evidential breath instruments (e.g., fuel-cell and infrared devices) that estimate blood alcohol concentration (BAC) by measuring alcohol in deep-lung air. The law presumes compliance with strict administrative rules under the California Code of Regulations (Title 17). Those rules govern instrument approval, operator qualifications, observation periods, accuracy checks, calibrating solutions, record-keeping, and the admissibility foundation for results. See 17 CCR forensic alcohol testing provisions.

The state’s implied-consent statute, Veh. Code §23612, requires a chemical test after a lawful DUI arrest. Whether the breath result is ultimately persuasive depends on proof that Title-17 requirements were met.

Key Title-17 requirements that often decide cases

• Observation (deprivation) period: Before an evidential breath test, the subject must be observed to ensure no regurgitation, belching, eating, drinking, smoking, or foreign material that could introduce “mouth alcohol.” Missed or poorly documented observation undermines reliability.
• Approved instruments & accuracy checks: The device must be on the state’s approved list and show regular accuracy checks at defined intervals using approved solutions/standards; out-of-tolerance results require corrective action before the device is used again.
• Operator qualifications: Only trained, permitted operators may run evidential tests; their training/permits and adherence to the instrument’s specific protocol must be documented.
• Records & traceability: Logs must document control checks, calibrating solutions (lot, value, expiration), simulator temperatures (if applicable), maintenance, and repairs. Gaps or inconsistencies weaken the foundation.

Scientific limits and physiological confounders

Breath testing assumes that deep-lung breath reflects blood alcohol via a population-average partition ratio (~2100:1). Real-world human variability—temperature, breathing patterns, hematocrit, pulmonary conditions—can shift the amount of alcohol measured in exhaled air. That is why strict method control (Title-17 procedures) matters so much.

• Mouth alcohol & GERD: Residual alcohol from recent drinking, reflux, or regurgitation can inflate readings unless the observation period is honored and a proper breath sample is taken.
• Breathing pattern effects: Hyperventilation or shallow breathing can alter alveolar concentration; operators are trained to obtain a continuous, adequate exhalation meeting instrument prompts.
• Medical & dental issues: Dental appliances or oral pathology can trap alcohol; respiratory illness can affect sampling. These warrant medical records and expert review.

Administration errors that create reasonable doubt

• Observation period not met or not recorded (e.g., officer multitasking, in-car tasks, or gaps on video).
• Improper sampling: failure to obtain end-expiratory (deep-lung) breath; short blows; ignoring instrument prompts for minimum sample volume/flow.
• Accuracy check out of tolerance without corrective action; missing or expired solution certificates; simulator temps out of spec (for wet-bath systems).
• Operator permit/training gaps or using non-approved mouthpieces/parts.
• Record-keeping defects: missing logs, incomplete device history, or untraceable control solutions.

How we challenge breath results in court and at the DMV

We subpoena Title-17 records (device logs, control/accuracy checks, solution certs, maintenance/repair), the operator’s permit and training, and all reports. We compare every step to the instrument’s protocol and Title-17. If the foundation is incomplete or the method non-compliant, we move to exclude or to reduce the weight of the result. In parallel, we use the same record to contest the DMV’s APS action on probable cause and reliability.

• Discovery & audit: obtain and chart control checks by date, expected value, tolerance, and corrective actions.
• Video & timing: confirm the observation period and sampling quality on body-cam/dash video.
• Expert integration: retain forensic toxicology support where needed to explain partition-ratio variability, mouth-alcohol dynamics, and sampling artifacts.

FAQs

Is there a fixed “error margin” the court accepts for breath tests?

No universal percentage applies. Courts look at whether Title-17 standards and instrument protocols were followed and whether accuracy checks and documentation establish reliability.

Does California require a 15-minute observation?

California requires an observation (deprivation) period before evidential breath testing and prohibits intake/regurgitation that could introduce mouth alcohol. The exact requirements come from Title-17 rules and the device protocol; we verify both in your records.

Can I win if I “blew over” 0.08?

Yes, if the State’s foundation is deficient (e.g., observation period missing, accuracy checks out of tolerance, operator unqualified) or if other evidence (rising BAC, timing) undercuts the per-se case.

Talk with Braden & Tucci

Breath testing is only as strong as its method. We align Title-17 discovery with courtroom and DMV strategy to attack weak results. Call (949) 996-0170 or visit our pages on DMV hearings and license suspension to start your defense.

Disclaimer: This article is for general information only and not legal advice. Outcomes depend on specific facts and jurisdiction.