Evidential Breath Testing

Drivers arrested on suspicion of DUI / DWI in California are offered the choice of an evidential breath test or a blood test. When motorists are arrested for DUID - driving under the influence of drugs, they will be offered a choice of a blood or a urine test. Many drivers choose the evidential breath test, and then fear that a drunk driving conviction is inevitable when the test shows a blood alcohol content (BAC) above the legal limit. Luckily, breath tests that show a BAC of .08 percent or greater can be successfully challenged by a skilled defense attorney. The experienced DUI / DWI lawyers at The Kavinoky Law Firm can effectively attack breath test results in a drinking and driving case.

Breath machines used in California drunk driving investigations vary from jurisdiction to jurisdiction. The equipment used includes the E-PAS - a hand-held unit that is often administered roadside - or a variety of stationhouse breath-testing machines, such as the Intoxilyzer 5000, the EC/IR, the Draeger, the BAC Datamaster, and many more.

Regardless of the type of machine used, all breath testing in drinking and driving cases is an indirect measurement of BAC. Breath testing devices produce an estimate of BAC through a conversion process, whereby a blood alcohol level is predicted on the basis of certain scientific assumptions, which may or may not be applicable to the person being tested. These scientific assumptions include drivers' blood/breath partition ratio, their breath temperature, and many other factors.

Since breath testing in DUI / DWI investigations always occurs sometime after the accused motorist was actually behind the wheel, which is the relevant time in a drunk driving case, the number only becomes meaningful through a process called retrograde extrapolation. Retrograde extrapolation is an attempt to look backward and give an opinion about the driver's alcohol level at the earlier time of driving based upon the later breath test results.

This type of speculation is rife with problems. Alcohol levels change over time, and the amount of change depends on many difficult to predict factors. Stomach contents, body weight, gender, the amount of alcohol consumed, the length of the drinking period, elimination or "burn-off" rate, and other personal metabolic factors all interfere with retrograde extrapolation in a DUI / DWI investigation.

For retrograde extrapolation to be accurate, the expert must assume that the accused drunk driver is in the "post-absorptive" phase - an assumption not always true, since the absorptive phase can last for two hours or more.

Breath test devices in DUI / DWI cases are of one of two types - infrared breath testing machines or fuel cell machines. When using the infrared device, the subject blows into a collection tube. Light passes from one end of the tube to the other, and the machine measures the amount of light beam that is diminished as it passes from one side to the other in the light spectrum of the alcohol molecule.

The fuel cell device testing machine measures the amount of oxidation that occurs on an electromagnetic chip, and then the amount of the electrical charge is converted to a number, which is supposed to represent the driver's BAC. Both methods of DUI / DWI breath testing are subject to many challenges, and a drunk driving criminal defense lawyer knows how to effectively question these results.

Some defenses acknowledge that the BAC reading is correct, but challenge whether the driver was under the influence of alcohol or exceeded the legal limit at the time of driving. Other defense strategies challenge the accuracy of the breath test result itself. A criminal defense drunk driving attorney will typically explore both avenues on behalf of his or her DUI / DWI client.

An experienced DUI / DWI defense attorney always questions the functioning of the breath test machine. Whether the machine is an Intoxilyzer 3000, Intoxilyzer 5000, Intoxilyzer 8000, EC/IR I or EC/IR II, a Draeger or a BAC Datamaster, the machine must be working properly to give a reliable result. This means ensuring that the calibration records, usage logs and maintenance history are all properly documented and don't reveal any problems.

An experienced California DUI / DWI defense lawyer from The Kavinoky Law Firm knows how to investigate potential problems in evidential breath test results. When problems are revealed, they may result in the breath test results being excluded, or can be used to lessen the weight of the evidence.