Evidential Breath Alcohol Testing

San Francisco driving under the influence (DUI) prosecutions rely exclusively on the Intoxilyzer 5000 breath alcohol testing device manufactured by CMI. The machine utilizes infrared technology to determine the blood alcohol level of individuals suspected of driving while impaired. The way the Intoxilyzer 5000 operates is by shining infrared energy (a light bulb) through an 88 cubic centimeter sample chamber (pipe) towards a detector positioned at the other end of the sample chamber. Molecules resembling alcohol absorb this infrared energy (light) which allows less energy to reach the detector. The difference between the amount of infrared energy expected to reach the detector and the amount which actually reaches the detector during a breath alcohol test is how the blood alcohol level is calculated.

Although all law enforcement agencies making DUI arrests in San Francisco rely on the Intoxilyzer 5000, the device is not infallible nor completely accurate. In fact, in November of 2005, a Florida court ruling disallowed use of the Intoxylizer 5000 because the manufacturer, CMI Inc., refused to provide information and details about how the device computes Breath Alcohol Content. Law enforcement agencies making arrests in Bay Area counties outside of San Francisco utilize a different breath alcohol tester called the Drager Alcotest 7110 MKIII-C. California law requires evidential breath tests to be conducted in compliance with California Code of Regulations. Title 17 is the governing section of the California Code of Regulations applicable to alcohol breath tests.

Additionally, scientific studies have been conducted which uncovered information discrediting the accuracy of the Intoxilyzer 5000. A medical doctor and professor specializing in Medical Forensics at Florida International University revealed several serious factors which undercut the reliability of the Intoxilyzer 5000 providing accurate readings. This study was published as "Variables Affecting Accuracy Precision of Breath Alcohol Instruments including Intoxilyzer 5000" (Rose & Furton).

First, the theory of Henry's Law and the 2100:1 ratio was attacked by stating "In order to understand the application of this Law, one needs to imagine a capped bottle containing water and a little ethanol. The bottle will contain the water and ethanol in two forms; liquid, and gas above the liquid. This law states that at equilibrium, one can measure the concentration of the ethanol in the gas phase, and from that measurement predict the concentration in the simultaneous liquid phase. The comparison being made is that the lungs are like the bottle, the blood in the lungs are like the liquid in the bottle, and the breath is like the gas phase above the liquid. Unfortunately, Henry's Law does not apply in the lungs."

The study further explained that since the exact conditions required to accurately create Henry's Law do not exist in the Intoxilyzer 5000, the ratio that is used to calculate intoxication (2100:1) is highly susceptible to false positives (indications that the subject's Blood Alcohol Level is substantially higher than it actually is).

The same study revealed that many additional factors including individual rate of metabolism of ethanol (alcohol), breathing, body and breath temperature, and presence of other compounds cannot be accounted for by the Intoxilyzer 5000 and only further increase the possibility of error.

While the Intoxilyzer 5000 may be the "Gold Standard" for law enforcement making DUI arrests in San Francisco, it is by no means absolute or incontrovertible evidence that a person was at a particular blood alcohol level at the time of driving. Accordingly, it is important that anyone arrested for driving under the influence of alcohol (DUI) who submitted to a breath test contact a qualified attorney with a background in DUI law and DUI defense.

Contact The Office

Mr. Tayac and the DUI investigators and experts working with him stand ready to help you or your family member. A member of the office is available to speak with you regarding the case any day of the week between the hours of 8:00 a.m. and 8:00 p.m. Pacific Standard Time at 415-552-6000.