9 Ways to Challenge Breath Test Evidence

Breath testing is the most widely used method of determining whether someone is above the legal limit for operating a motor vehicle after consuming alcohol. But its scientific basis has been questioned. This list provides defense counsel with several ways to challenge breath test evidence.

  1. The breath sample’s quality. The quality of the sample of breath measured is probably the most important element of the breath test. California law requires certain safeguards to ensure the integrity of the breath sample, e.g., the regulations require that two separate breath samples be taken from each person tested and that the results be within 0.02 percent of each other. 17 Cal Code Regs §1221.2(a)(1).
  2. Temperature’s effect on the breath sample. Body temperature and therefore breath temperature will affect the number of alcohol molecules distributed between the blood and the alveolar breath (the respiratory gases in an alveolus of the lung collected while the last portion of air is expelled by maximum exhalation) as well as the equilibrium in the airway (throat).
  3. Breath sample contamination by mouth alcohol. Interference by alcohol in the mouth may occur from recent drinking, burping, belching, or regurgitation when alcohol is present in the stomach. The potential for mouth alcohol contamination is addressed in 17 Cal Code Regs §1221.1, which requires certain precautions to be taken to help avoid mouth alcohol contamination during the testing process.
  4. Violation of the 15-minute rule. California Code of Regulations attempts to ward off mouth alcohol contamination of breath tests by requiring that “[t]he 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.” 17 Cal Code Regs §1221.1(b)(1). If regurgitation, belching, or any other potential mouth alcohol–generating event occurs, the 15-minute period should be started again from the beginning. The defense can argue that regurgitations (and burps in particular) may easily be missed in the 15 minutes before the breath test.
  5. Error in or lack of slope detector. Some instruments have a feature called a slope detector, which is capable of detecting mouth alcohol levels that can skew breath test results. In theory, this slope detector should solve the problem of skewed results, but studies have criticized the effectiveness of the slope detector.
  6. Existence of Gastroesophageal Reflux Disease (GERD). GERD is a condition in which ethanol in the gut may reflux up into the mouth, causing mouth alcohol interference with breath testing. There’s dispute about how GERD affects breath alcohol testing, and only a few studies have been published in scientific literature.
  7. Metabolic and dietary defenses. (1) Diabetes may cause the level of blood sugar to drop to such a level that the body begins to oxidize fat to create sugar; this process eliminates ketones as a waste product, which can be converted into isopropyl, which can be misinterpreted by fuel cell breathalyzers; (2) Diets that emphasize low carbohydrate and high protein consumption result in elevated levels of acetone that can be converted into isopropanol and mistakenly identified by fuel cell breathalyzers as ethanol; and (3) gastric bypass surgery used to help obese people lose weight has been found to cause higher peak blood alcohol concentrations and requires more time to reach a zero blood alcohol concentration.
  8. Breath testing margin of error. Body temperature, blood viscosity, breathing technique, determination of the known value in a solution used for calibration, and temperature of the solution used for calibration in a simulator device may all contribute to the potential for error.
  9. Assumed partition ratio of breath to blood alcohol. Breath testing machines assume that the ratio of alcohol in blood to breath is 2100:1. However, breath alcohol result obtained from a breath test performed during the absorptive phase can significantly overstate the actual blood alcohol concentration.

Get citations and more detailed information for each of these challenges in Scientific Evidence and Expert Testimony in California, chap 3, and get an overview of DUI cases in California Criminal Law Procedure and Practice, chap 55. Both of these titles are part of CEB’s OnLAW Criminal Law Library.

Other CEBblog™ posts you may find useful:

© The Regents of the University of California, 2018. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited.

2 thoughts on “9 Ways to Challenge Breath Test Evidence

  1. Pingback: Getting the Most Out of Your Preliminary Hearing | CEBblog™

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