HOW CAN THEY CHARGE ME WITH HAVING A BAC OF .08 WHEN I WAS UNDER THE LIMIT?

Q: How likely will you be convicted of a DUI when the machine shows your blood alcohol content (BAC) was below 08?
Q: Can you get charged with a DUI with a BAC below 0.08%?
Benjamin F. Warlick got into a traffic accident, and California Highway Patrol Officer Chris Jensen came to investigate.
Mr. Warlick told the CHP officer he had been drinking alcohol earlier in the evening. The reading from a preliminary alcohol screening (PAS) test showed 0.07 percent at 12:17 a.m.
The prosecution charged Mr. Warlick with violating California Vehicle Code Section 23152(b), which says it is:
“unlawful for any person who has 0.08 percent or more, by weight, of alcohol in his or her blood to drive a vehicle.”
Warlick's DUI defense attorney made a motion to exclude any expert testimony based on retrograde extrapolation analysis.
At the pretrial hearing, Marisa Ochoa, an employee of the San Diego County Sheriff's Department, known as a criminalist, testified for the prosecution.
Q: How Can They Charge Him For Having a BAC over .08 if the Breathalyzer reading was .07?
A: Ms. Ochoa testified that based on the .07 test result, Mr. Warlick's statements about his drinking, and studies regarding normal alcohol elimination ratesA, Ms. Ochoa's opinion was that Mr. Warlick had a BAC of at least 0.08 percent at the time of driving.
Judge Edward P. Allard III ruled Ms. Ochoa's proposed testimony was inadmissible based on Baker v. Gourley (2002) 98 Cal.App.4th 1263. Judge Allard said, according to the Baker case, a violation of Section 23152(b) cannot be proved without a chemical test showing a blood-alcohol level of 0.08 percent or greater.
Based on the court's ruling, the prosecutor told the court that he could not prove a violation of Section 23152(b) without retrograde extrapolation1 evidence.
To answer the questions above, no matter what the results of your breath or blood tests are, you can count on the prosecution to bring in a witness who will testify that your BAC at the time you were driving was higher compared to the results of the tests.
The trial court dismissed the charge. The prosecution appealed.

The Appellate Division of the Superior Court in San Diego disagreed with the trial court. It said that Baker v. Gourley did “not stand for nearly so sweeping a proposition.” It further said, “The Baker decision is limited by its terms to the “so-called ‘ Admin Per Se" laws where the … [DMV] suspends a driver's license…” Read more about DMV Admin Per Se Hearings
In distinguishing Baker, the Appellate Division also noted,
“the factual context of that case is of crucial importance in understanding the scope of the holding. Baker's statement precluding reliance on circumstantial evidence was based expressly on the lack of a “valid chemical test. Here, in contrast, there was a perfectly valid chemical test—that happened to show a blood-alcohol level of only 0.07 percent.”
The court's characterization of the PAS test as a "valid chemical test" is puzzling.
Vehicle Code Section 13388 says “a preliminary alcohol screening test device is an instrument designed and used to measure the presence of alcohol in a person based on a breath sample.”
Vehicle Code Section 23612(h) says, “A preliminary alcohol screening test that indicates the presence or concentration of alcohol based on a breath sample in order to establish reasonable cause to believe the person was driving a vehicle in violation of ... is a field sobriety test and may be used by an officer as a further investigative tool.”
Vehicle Code Section 23612 (a) (1) says a chemical test comes after arrest: “A person who drives... is deemed to have given his or her consent to chemical testing of his or her blood or breath for the purpose of determining the alcoholic content of his or her blood, if lawfully arrested for an offense... in violation of Section 23152 …”
"See Vehicle Code section 23612, subdivision (h) (a preliminary alcohol screening test (PAS) is an investigative tool used to determine whether there is reasonable cause for arrest). As explained in 72 Ops.Cal.Atty.Gen. 226, 227 (1989), a preliminary test is “distinguished from the chemical testing of a driver's blood, breath or urine contemplated by the implied consent law (Veh. Code, § [23612]) which is administered after the driver is arrested, [and is] sometimes referred to as ‘evidentiary' [or evidential] testing.”" People v. Vangelder, (2013) 58 Cal. 4th 1, FN 1.
Despite the above authorities, the Appellate Division reversed the trial court.
It reinstated the Section 23152(b) charge and denied the request to exclude the retrograde extrapolation testimony.
Interesting Note: The California Supreme Court says, "Subjects are instructed to take and expel a deep breath." Vangelder at p. 17, citing State v. Chun (2008) 194 N.J. 54, 943 A.2d 114 at p. 129. However, on page 15 of the Owner's Manual for the DataMaster DMT breath testing machine, it says, "The operator should advise the subject as follows: “Take a normal breath..."
The citation for this opinion is People v. Warlick (2006) 162 Cal. App. 4th Supp. 1.
WHAT EXPERTS HAVE SAID ABOUT RETROGRADE EXTRAPOLATION
"Among the many reasons for the infeasibility of retrograde extrapolation, three stand out: 1) lack of knowledge… about the time of the alcohol concentration peak and absorption-postabsorption status, 2) ignorance about the mathematical characteristics and mean rate of change of the individual's blood or breath alcohol elimination curve, and 3) unpredictable irregularities of the curve, especially short term fluctuations from the best-fit trend line of the blood or breath alcohol curve.”2
“...No forensically valid forward or backward extrapolation of blood or breath alcohol concentrations is ordinarily possible in a given subject and occasion solely on the basis of time and individual analysis results.”3
“The status of ethanol absorption is an important consideration when attempts are made to estimate (BEC) blood ethanol concentration at the time of the offense from the blood ethanol concentration determined at time of sampling. This technique is called back tracking BEC, or retrograde extrapolation, and is a dubious practice.”4
Forensic toxicologists and other experts perform calculations related to alcohol. Numerous factors must be taken into consideration when experts provide estimates related to alcohol concentrations. Calculations experts perform are retrograde extrapolation, forward estimations, and minimum drinks consumed to reach a BAC.
Standard drink is defined as a beverage containing approximately 14 grams of alcohol. e.g. 12 ounces, 5% beer; 5 ounces, 12% wine; 1.5 ounces, 80 proof liquor (40%).5
If you've been arrested for a DUI, contact The Law Office of Richard Wagner at (714) 721-4423.
AUTHORITIES
A 4.1.3 Elimination Alcohol is primarily eliminated via enzyme metabolism in the liver; however, a small amount is removed through first pass metabolism or excreted unchanged in the breath, sweat, oral fluid, and urine...The linear rate can only be applied when ... the subject is post absorptive. While the AC may be declining after the subject reaches their peak AC (post peak), the linear rate is not applicable until the post absorptive state. 4.1.3.1 An elimination rate range of 0.010 – 0.025 g/dL/hour encompasses the majority of the population regardless of age, sex, ethnicity, and drinking experience. Guidelines for Performing Alcohol Calculations in Forensic Toxicology, Forensic Toxicology Subcommittee, Organization of Scientific Area Committees (OSAC) for Forensic Science, April 2022
1 ANSI/ASB Best Practice Recommendation 122, 1st Ed. 2024, Best Practice Recommendation for Performing Alcohol Calculations in Forensic Toxicology, 5.4.1, "Retrograde extrapolation is a mathematical process that uses an alcohol concentration at a given point in time and estimates what the concentration would have been at an earlier time. It is not possible to calculate the exact alcohol concentration at an earlier point in time, but an estimation in the form of a concentration range can be provided."
2 Dubowski, K.M., “Absorption, Distribution, and Elimination of Alcohol: Highway Safety Aspects," Journal of Studies on Alcohol Supplement No. 10: 103, July 1985.
3 Dubowski, K.M., “Absorption, Distribution, and Elimination of Alcohol: Highway Safety Aspects," Journal of Studies on Alcohol Supplement No. 10: 106, July 1985.
4 Jones, A.W., Jonsson, K.A., and Neri, A., "Peak Blood-Ethanol Concentration and the Time of Its Occurrence After Rapid Drinking on an Empty Stomach” Journal of Forensic Sciences, Vol. 36. No. 2: 376-377, March 1991.
5. See Note A, above, Sec. 4.5.