Breathalyzer results are often the prosecution's key evidence in DUI cases, but these devices are far from infallible. Understanding how breath testing works and its limitations provides multiple avenues for challenging BAC evidence.
How Breathalyzers Work
Breathalyzers measure alcohol in breath and use a partition ratio to estimate blood alcohol content. The devices assume a fixed ratio between breath alcohol and blood alcohol—typically 2100:1, meaning 2100 milliliters of breath contains the same alcohol as 1 milliliter of blood.
This assumed ratio doesn't hold true for everyone. Actual partition ratios vary from about 1100:1 to 3400:1 depending on body temperature, breathing patterns, and individual physiology. Using a fixed ratio produces inaccurate results for many people.
Common Sources of Error
Mouth alcohol from recent drinking, dental work trapping alcohol, or gastric reflux can produce falsely elevated readings. Residual mouth alcohol should dissipate during the required observation period, but officers don't always observe continuously.
Interfering substances can trigger false readings. Breath fresheners, mouthwash, cough medicine, and certain medical conditions produce compounds that breathalyzers may mistake for alcohol.
Breathing patterns affect results. Deep breaths before testing reduce readings; holding breath increases them. Officers may instruct suspects in ways that elevate results.
Body temperature changes readings. Fever or exercise that elevates body temperature increases breath alcohol readings even without additional alcohol consumption.
Device Maintenance Issues
Breathalyzers require regular calibration and maintenance. Poorly maintained devices produce unreliable results. Defense challenges may reveal calibration records show the device was out of specification, maintenance was overdue at the time of testing, the device had known problems or repair history, and required software updates weren't installed.
Departments must maintain records of calibration, maintenance, and repairs. Obtaining these records through discovery is essential for challenging breath test evidence.
Operator Errors
Officers must be trained and certified to operate specific breathalyzer models. Operator errors include failing to observe the required pre-test waiting period, improper device operation, failure to verify the device is functioning correctly, not administering the required number of tests, and improper handling of test results.
Operator certification and training records may reveal inadequate qualifications to administer tests properly.
Rising Blood Alcohol Defense
Alcohol takes time to absorb into the bloodstream. If you drank shortly before driving, your BAC may have been below the legal limit while driving but continued rising after you stopped. The relevant BAC is your level while driving, not when tested.
Expert testimony about absorption rates can establish that your BAC was below 0.08% at the time you were actually driving, even if the later test showed higher.
Challenging Test Admissibility
Breath test results may be excludable if the device wasn't on the state's approved list, the operator lacked proper certification, required procedures weren't followed, the device wasn't properly calibrated, or the observation period was inadequate.
Excluding breath test results often forces dismissal or significant charge reduction when the prosecution loses its primary evidence.
Expert Witnesses
Toxicologists and forensic experts can testify about breathalyzer limitations, specific factors affecting your test results, rising blood alcohol, and whether your BAC was actually above the legal limit while driving.
Expert testimony counters the prosecution's presentation of breath tests as definitive proof, showing juries the uncertainty inherent in these measurements.
Building Your Defense
Challenging breathalyzer evidence requires obtaining maintenance and calibration records for the specific device, reviewing operator training and certification, analyzing testing procedures for compliance with requirements, and identifying individual factors that may have affected your results.
An experienced DUI attorney knows what records to subpoena and how to identify errors that undermine breath test reliability.