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Inherent Error in DUI Breath and Blood Alcohol Testing

Even if the proper procedures were correctly followed in a drunk driving case for the blood, breath, or urine test, even if the instruments and/or computer systems used were functioning perfectly, and even if all chemicals, blanks, and standards were of the proper quantity and quality, blood-alcohol analysis in DUI investigations is not a perfect process. Thus it is generally recognized by scientists that such analytical methods have an inherent, or built-in, error factor. This, of course, should be brought out for the jury in DUI trials.

In People v. Campos, 138 Cal. App. 3d Supp. 1, 188 Cal. Rptr. 366 (1982), a California superior court held that a .110 percent per se case should be dismissed as a matter of law due to the inherent margin for inaccuracy in testing after a DUI suspect submitted to a blood test that resulted in a reading of. 10 percent, and the wet chemical method used had an inaccuracy rate of plus or minus .005 percent. Accordingly, the court noted that it was impossible to determine the alcohol content more precisely than that it was at some figure between .095 percent and .105 percent.

The court began its analysis by noting that the .10 issue in DUI cases was one of first impression in California. In reaching its result, the court reviewed DUI cases from Delaware, Nebraska, and Hawaii:

In State v. Rucker, (1972 Del. Super. Ct.) 297 A.2d 400, a Delaware statute made it unlawful for a person to drive a motor vehicle while such person's blood has reached a blood alcohol concentration of 'Ao of 1 percent or more, by weight, as shown by a chemical analysis of a blood, breath, or urine sample taken within 4 hours of the alleged offense . Defendant had taken a breath test which showed a reading of .104 percent, but the test procedure had a margin of error of plus or minus .009 percent... [T] he Delaware court observed that the statute did not purport to create a presumption. It simply makes a blood alcohol concentration of 0.100 percent, or more as shown by specified types of tests, an element of the offense. If one has that concentration while driving, as determined b the test specified in the statute and if that test was administered within 4 hours after the alleged offense, 21 Del. C. Section 4176 directs that such person 'shall be guilty.' The court viewed the function of the trier of fact as limited to determining whether the test results in drunk driving cases showed the required percentage of alcohol in the blood, but the trier of fact is not free to disregard the mandate of the statute or to question the wisdom of the General Assembly in providing that test results constitute proof of that element of the crime. It assumed that the Delaware General Assembly, in making the test result determinative, had taken into consideration the possibility of variations between the test results and the actual blood-alcohol content of the accused when it enacted the DUI statute.

In State v. Bjornsen (1978 Neb.) 271 N.W.2d 839, a majority of the Supreme Court of Nebraska reached a conclusion contrary to Rucker under a Nebraska drunk driving statute worded similarly to the Delaware statute. It, too, made unlawful a person's operation of a motor vehicle when that person has ten-hundredths of one percent or more by weight of alcohol in his body fluid as shown by chemical analysis of his blood, breath or urine. Defendant's chemical test resulted in a reading of .10 percent blood-alcohol content, but the state's criminalist testified that the reading could have been off as much as .005 percent, so that defendant's blood alcohol could have been as low as .095 percent. The prosecutor argued that, under the statute, so long as the chemical test result showed .10 percent or more any inaccuracies in the DUI testing procedures were irrelevant. The court held: While the legislature has the acknowledged right to prescribe acceptable methods of testing for alcohol content in the body fluids and perhaps even the right to prescribe that such evidence is admissible in a court of law, it is a judicial determination as to whether this evidence is sufficient to sustain a conviction. The Legislature has selected a particular percent of alcohol to be a criminal offense if present in a person operating a motor vehicle. It is not unreasonable to require that the test, designed to show that percent, do so outside of any error or tolerance inherent in the testing process, 271 N.W.2d at 840.

The California court also considered the Hawaiian case of State v. Boehmer, 613 P.2d 916 (1980). In that DUI case, the court of appeals of Hawaii recognized a .0165 percent error factor in the Breathalyzer test. The defendant had a blood-alcohol reading of .11. percent. The court, relying on the heavy burden of proof that the prosecutor has in a criminal case, reasoned further that the margin of error of the Breathalyzer test means that on any given test the DUI defendant's actual blood-alcohol content could be .0165 percent more or less than the reading shown by the test. Thus, the inherent margin of error could put defendant's actual blood alcohol below the level necessary for the presumption to arise. In its conclusion, the court cited with approval State v. Bjornsen, 201 Neb. 709, 271 N.W.2d 839 (1978), which held that in order for the statutory presumption to arise, the results of such tests when taken together with its tolerance for error, must equal or exceed the statutory level. 271 N.W.2d at 840.

The Campos court reasoned that the difference between the Rucker and Bjornsen decisions was one of statutory interpretation. In Rucker, the Delaware court interpreted the DUI law as making the test reading the conclusive factor. In Bjornsen, the Nebraska court interpreted the DUI law as requiring a blood-alcohol content of .10 percent or more. In holding that the .10 reading should be dismissed, the California court sided with the Nebraska and Hawaii courts. In the words of the court:

More recently, the Alaskan Supreme Court has held that DWI chemical test results that would be below .10 percent after applying the inherent margin of error could not be used as the basis for a license revocation. Haynes v. Department of Public Safety, 865 P.2d 753 (Alaska 1993). In that case, the breath test result on an Intoximeter 3000 in a DWI case was .106 percent; the recognized inherent error was .01 percent per 210 liters of breath. Thus the actual BAC could have been anywhere from .096 percent to .116 percent. Holding that the margin of error in DWI cases must be applied in the driver's favor, the court concluded that there was insufficient evidence to find a BAC of .10 percent or higher.

However, see King v. Commonwealth, 875 S.W.2d 903 (Ky. App. 1993), involving a reading of .100 percent on an Intoxilyzer 5000. The court in a DUI trial found the margin of error to be only .005 percent, and the .100 percent reading was thus accurate enough to be of probative value. The appellate court concluded that to exclude a reading with such a small margin of error in a DUI would be requiring the prosecution to prove guilt beyond any doubt. Query: Would the Kentucky appellate court have come to a different conclusion if the recognized inherent error was .01 rather than .005?