A breathalyzer reading above 0.08% can feel like the end of a DUI case before it starts. What many drivers in Virginia Beach do not realize is that breathalyzers do not measure alcohol in the blood directly. They estimate it, using a set of assumptions that can be wrong under specific circumstances.
How breathalyzers work
Breathalyzers rely on Henry’s Law, which describes the relationship between the concentration of a substance dissolved in liquid and its concentration in the air above that liquid. When you blow into the device, it captures deep lung air and measures ethanol content using either infrared spectroscopy or electrochemical fuel cell technology. That reading is then converted to an estimated BAC using a standardized 2,100:1 ratio. This ratio varies among individuals, typically ranging from 1,900:1 to 2,400:1, which introduces a margin of error before any other variables are considered.
Where breathalyzer readings can break down
Several factors can distort results in ways that are legally relevant:
- Mouth alcohol from recent drinking, burping, acid reflux, or GERD can contaminate the breath sample and inflate the reading
- Calibration and maintenance failures can cause the device to drift out of accuracy; the Virginia Department of Forensic Science regulates testing schedules for this reason
- Failure to observe the required 20-minute pre-test observation period, during which the subject must not vomit, belch, or place anything in their mouth, can invalidate results
- Medical conditions such as diabetes or hypoglycemia, and diets that are very low in carbohydrates, can produce elevated acetone levels that some breathalyzer models register as ethanol
- A rising BAC at the time of testing means the reading at the station may not reflect what it was at the time of driving
Each of these issues can form the basis of a legitimate legal challenge depending on the facts of the case.
What a breathalyzer result actually means in court
A breathalyzer reading is an estimate generated by a machine that depends on proper maintenance, correct operation, and biological assumptions that do not apply equally to every person. A result above the legal limit does not make a case unwinnable. If you are facing DUI charges in Virginia Beach, a DUI defense attorney can review the testing records, calibration logs, and procedural compliance in your case to determine whether the results can be challenged.