Blood Alcohol Concentration
You may have seen or read about “BAC” when doing research on Driving Under the Influence, drunk driving, blood alcohol level, and chemical test results, but maybe you have some further questions about BAC. Hopefully, you find answers here.
BAC stands for Blood-Alcohol Concentration. The alcohol concentration in your blood can be shown in different ways. The most common way is weight per volume, or grams/volume of blood. In California, this is shown as grams / 100 milliliters of blood, gram % or percent (W/V), and grams per 210 liters of breath or g/210 L breath.1
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The Three Hour Presumption
The movement of alcohol in the body, its absorption into the bloodstream, its metabolism, and its elimination are all dynamic processes. However, in California, there is a rebuttable presumption that says the person had 0.08 percent (or more) in his or her blood at the time of driving if the person had 0.08 percent in his or her blood at the time of the chemical test within three hours after the driving.2
Although there is little science to justify this presumption, it still applies in court and at the DMV. However, the key is that this presumption is rebuttable. That is where your DUI Lawyer plays a critical role.
It is just as likely that your BAC may be rising, falling, or staying the same over the same time period.
DUI Attorneys often consult with forensic toxicologists, who are experts on BAC. These discussions cover estimates about what a drinker's possible BAC might be when the person was driving and/or taking the chemical tests (breath or blood tests).
There are formulas used for these estimates, and there are also factors and assumptions that can have an effect on the calculations.
It is sometimes useful to estimate how many drinks someone would have to drink to be at a certain BAC. Wine is generally 12% alcohol, while beer is about 4%. You can say that 4 ounces of wine (glass of wine) has the equivalent alcohol content to a 12-ounce beer. Furthermore, 1.25 ounces of 80-proof liquor (40% alcohol) is equal to 1 ounce of 100-proof liquor (50% alcohol).
Many experts warn of the dangers associated with what is called “extrapolating” to past BAC levels. If all that is known is the time you were pulled over by the police and the chemical test result, Dr. Kurt Dubowksi, the University of Oklahoma Distinguished Professor of Medicine and Director of Toxicology Laboratories at the University of Oklahoma, says that “no forensically valid forward or backward extrapolation… is ordinarily possible.”3
BAC Laws in California
When the prosecutor charges you with a DUI, the BAC is significant evidence against you. It is illegal to drive with a BAC of 0.08 percent or more.4
It is illegal for someone under 21 to drive with a BAC of 0.05 percent or more.5 It is also against the law for a person under 21 to drive with a BAC of 0.01 percent or more.6
It is illegal to drive with a blood-alcohol concentration of 0.08 percent, or higher and cause injury to someone else.7
It is against the law for commercial drivers and “passenger for hire” drivers to drive with a BAC of 0.04 percent or more.8
High BAC Enhancement
A BAC of 0.15 percent9 and 0.20 percent10 will cause the prosecutor to file sentence enhancements for high BAC. This is how the prosecutor signals to the judge to increase your penalties under California law.
If you face this situation, it is highly recommended that you call DUI Attorney Richard Wagner at (714) 721-4423.
Potential challenges to BAC evidence:
Attacks on Breath Tests
If you took a breath test while in the absorptive phase, your breath alcohol concentration (BrAC) would be higher than your BAC.11
There can also be alcohol contamination in your mouth by recent drinking, regurgitation, burping, or vomiting. If the officer failed to properly administer the breath test to you, the BAC results are unreliable.
The breath sample shall be collected only after fifteen continuous minutes, during which time the subject must not have ingested alcoholic beverages or other fluids, regurgitated, vomited, eaten, or smoked.12
A DUI Defense attorney should also review the calibration records of the breath machine to see if it was properly maintained.
Read more about Understanding DUI Breath Testing in California
Attacks on Blood Tests
If you took a blood test, DUI Defense Attorneys attack the collection, transportation, and storage of your blood sample.
- Was the person who took your blood qualified to draw your blood?
- Was your blood taken in a reasonable manner according to acceptable medical practices?
- Was your sample properly preserved?
Alcohol in the blood vial can be produced by contamination. Alcohol can be produced by fermentation.13 The device analyzing your blood cannot tell where the alcohol came from. Therefore, the lab report may not reflect your actual BAC.
Read more: Understanding DUI Blood Tests in California
LEGAL AUTHORITIES
1 California Vehicle Code Section 23152(b), "For purposes of this article ..., percent, by weight, of alcohol in a person's blood is based upon grams of alcohol per 100 milliliters of blood or grams of alcohol per 210 liters of breath."
2 California Vehicle Code Sections 23152(b) and 23153(b), "In any prosecution under this subdivision, it is a rebuttable presumption that the person had 0.08 percent or more, by weight, of alcohol in his or her blood at the time of driving the vehicle if the person had 0.08 percent or more, by weight, of alcohol in his or her blood at the time of the performance of a chemical test within three hours after the driving."
3 Kurt M. Dubowski, Ph.D., "Absorption, Distribution and Elimination of Alcohol: Highway Safety Aspects," Journal of Studies on Alcohol, (July 1985), p. 106.
4 California Vehicle Code Section 23152(b), "It is unlawful for a person who has 0.08 percent or more, by weight, of alcohol in his or her blood to drive a vehicle."
5 California Vehicle Code Section 23140(a), "It is unlawful for a person under the age of 21 years who has 0.05 percent or more, by weight, of alcohol in his or her blood to drive a vehicle."
6 California Vehicle Code Section 23136(a), "Notwithstanding Sections 23152 and 23153, it is unlawful for a person under the age of 21 years who has a blood-alcohol concentration of 0.01 percent or greater, as measured by a preliminary alcohol screening test or other chemical test, to drive a vehicle."
7 California Vehicle Code Section 23153(b), "It is unlawful for a person, while having 0.08 percent or more, by weight, of alcohol in his or her blood to drive a vehicle and concurrently do any act forbidden by law, or neglect any duty imposed by law in driving the vehicle, which act or neglect proximately causes bodily injury to any person other than the driver."
8 California Vehicle Code Section 23152(d), "It is unlawful for a person who has 0.04 percent or more, by weight, of alcohol in his or her blood to drive a commercial motor vehicle, as defined in Section 15210. In a prosecution under this subdivision, it is a rebuttable presumption that the person had 0.04 percent or more, by weight, of alcohol in his or her blood at the time of driving the vehicle if the person had 0.04 percent or more, by weight, of alcohol in his or her blood at the time of the performance of a chemical test within three hours after the driving."
California Vehicle Code Section 23152(e), "Commencing July 1, 2018, it shall be unlawful for a person who has 0.04 percent or more, by weight, of alcohol in his or her blood to drive a motor vehicle when a passenger for hire is a passenger in the vehicle at the time of the offense. For purposes of this subdivision, “passenger for hire” means a passenger for whom consideration is contributed or expected as a condition of carriage in the vehicle, whether directly or indirectly flowing to the owner, operator, agent, or any other person having an interest in the vehicle. In a prosecution under this subdivision, it is a rebuttable presumption that the person had 0.04 percent or more, by weight, of alcohol in his or her blood at the time of driving the vehicle if the person had 0.04 percent or more, by weight, of alcohol in his or her blood at the time of the performance of a chemical test within three hours after the driving."
9 California Vehicle Code 23578, "In addition to any other provision of this code, if a person is convicted of a violation of Section 23152 or 23153, the court shall consider a concentration of alcohol in the person's blood of 0.15 percent or more, by weight, ... as a special factor that may justify enhancing the penalties in sentencing, in determining whether to grant probation, and, if probation is granted, in determining additional or enhanced terms and conditions of probation."
10 California Vehicle Code Section 23538(b)(2), "The court shall refer a first offender whose blood-alcohol concentration was 0.20 percent or more, by weight, ... to participate for at least nine months or longer, as ordered by the court, in a licensed program that consists of at least 60 hours of program activities, including those education, group counseling, and individual interview sessions ..."
11 Gerald D. Simpson, "Accuracy and Precision of Breath Alcohol Measurements for a Random Subject in Postabsorptive State," Clinical Chemistry 33/2, 261-268 (1987).
12 17 CCR 1221.1(b)(1), "The breath sample shall be collected only after fifteen continuous minutes during which time the subject must not have ingested alcoholic beverages or other fluids, regurgitated, vomited, eaten, or smoked."
13 Blume, P. and Lakatua, D.J., "The effect of microbial contamination of the blood sample on the determination of ethanol levels in serum," Am. J. Clin. Path. 60:700-702 (1973); Chang, R.B. et al, "The stability of ethyl alcohol in forensic blood specimens," J. Anal. Toxicol. 8:66-67 (1984).
