Blood Alcohol Concentration (BAC) Testing & Breathalyzer Calibration Accuracy
In DUI prosecutions, the numerical Blood Alcohol Concentration (BAC) reading forms the bedrock of per se impairment charges under California Vehicle Code § 23152(b) and counterpart statutes nationwide. Challenging breath test results requires forensic scrutiny of device calibration, operator error, and physiological variances.
1. The Science Behind Electrochemical & Infrared Devices
Evidentiary breath test instruments (such as the Intoxilyzer 8000 and Draeger Alcotest 9510) measure alcohol in deep lung alveolar air and apply an assumed 2,100:1 partition ratio to estimate venous blood alcohol. However, physiological deviations between individuals often skew these mathematical approximations.
| Defense Challenge | Scientific Basis | Legal Impact |
|---|---|---|
| 20-Minute Deprivation Violation | Mouth alcohol from GERD, dental work, or burping artificially spikes readings | Suppression of breath sample under Title 17 compliance rules |
| Partition Ratio Variance | Actual human ratios vary between 1,500:1 and 3,000:1 | Demonstrates actual blood BAC was below 0.08% threshold |
| Radio Frequency Interference (RFI) | Police radios and cell towers distort detector microcircuits | Invalidates machine accuracy certification |
| Calibration Drift & Log Errors | Failure to perform diagnostic accuracy checks every 10 days or 150 uses | Excludes chemical test evidence at trial |
⚖️ Statutory Precedent
Under established evidentiary standards, prosecutors bear the burden of proving that chemical testing equipment complied strictly with statutory calibration and maintenance mandates at the exact time of testing.
Authored & Verified by Duiattorneysonline Senior Trial Counsel
Our legal research desk analyzes Title 17 forensic compliance standards, NHTSA standardized field sobriety test administration manuals, DMV administrative per se hearing precedents, and Fourth Amendment search and seizure suppression strategies.