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New Zealand's breath and blood alcohol testing programs: further data analysis and forensic implications
A R Stowell1, A R Gainsford, R G Gullberg
1Environmental Science and Research Ltd (ESR), P.O. Box 50348, Porirua, New Zealand. allan.stowell@esr.cri.nz
Forensic Science International
|March 28, 2008
Summary
This study found that breath alcohol concentration (BrAC) testing can be highly accurate for drivers when accounting for alcohol clearance. Time-adjusted BrAC results significantly reduced false positives, improving the reliability of evidential breath testing.
Area of Science:
- Forensic Science
- Toxicology
- Analytical Chemistry
Background:
- Breath alcohol concentration (BrAC) is commonly used in law enforcement to assess driver impairment.
- Variability exists between BrAC and blood alcohol concentration (BAC) measurements due to factors like sampling time.
- Accurate BrAC measurement is crucial for legal and public safety purposes.
Purpose of the Study:
- To evaluate the accuracy of BrAC measurements compared to BAC.
- To determine the rate of false-positive BrAC results.
- To assess the impact of time-adjusted BAC values on BrAC accuracy.
Main Methods:
- Paired BAC and BrAC measurements from 11,837 drivers were analyzed.
- Duplicate BAC measurements used headspace gas chromatography.
- Duplicate BrAC measurements used infrared analyzers (Intoxilyzer 5000, Seres 679T, Seres 679ENZ).
- BAC values were time-adjusted using an assumed blood alcohol clearance rate.
Main Results:
- Without time adjustment, the false-positive BrAC rate (BrAC > BAC) was 31.3%.
- After time adjustment (0.019 g/dL/h clearance rate), the false-positive rate decreased to 2.8%.
- Harmful false-positives (BrAC > 0.1 g/210L, BAC ≤ 0.1 g/dL) were 0.14%, reduced to 0.04% when using the lower of duplicate BrAC results.
Conclusions:
- Time-adjusting BAC significantly improves the accuracy of BrAC measurements.
- Using the lower of duplicate BrAC results minimizes harmful false positives in evidential breath testing.
- BrAC testing, when properly adjusted, is a reliable method for assessing driver alcohol levels.
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