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Evidential Breath Test

Evidential Breath Tests, or EBTs, are the most commonly used breath-testing devices in California DUI cases. However, even though police and prosecutors rely heavily on EBTs, they aren't as ironclad as many people believe. A California criminal attorney who concentrate on Driving Under the Influence (DUI) defense can successfully challenge the results results of both blood and breath testing.

When someone is arrested for drunk driving, the breath machine they will be tested on will vary from jurisdiction to jurisdiction. In California, Driving Under the Influence (DUI) investigation may be based on many different breath test machines, including 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.

Breath testing in DUI cases is an indirect measurement of blood alcohol content (BAC). Breath testing devices all engage in 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, arrested, and prosecuted for drunk driving, or driving under the influence of alcohol. These scientific assumptions include drivers’ blood/breath partition ratio, their breath temperature, and many other factors.

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Attorneys for the firm represent clients accused of driving under the influence of alcohol or driving with a blood alcohol level at or above the legal limit in San Francisco, San Mateo, Marin, Alameda, Santa Clara, Contra Costa, Sonoma and Napa counties.

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Breath testing in a California DUI investigation always takes place after the time of driving (which is, of course, the relevant time in a drunk driving case), the number only becomes relevant through a process called retrograde extrapolation. Retrograde extrapolation is where the prosecution attempts to look backwards and give an opinion about the allegedly drunken driver’s alcohol level at the earlier time of driving based upon the later breath test results.

There are significant problems with this type of speculation. Alcohol levels change over time, and the manner in which they change is subject to much variation. Stomach contents, the amount of alcohol consumed, the length of the drinking period, body weight, gender, elimination or “burn-off” rate, and other personal metabolic factors all interfere with retrograde extrapolation in a DUI arrest.

There are many challenges to breath testing in California DUI cases. Some of the defenses assume the truth of the results, but challenge whether the driver was under the influence of alcohol or exceeded the legal limit at the time of driving. Other attacks relate to the accuracy of breath test results in the first place. An experienced DUI defense lawyers will typically explore both avenues on behalf of a client.

The first place to look when challenging a DUI or DWI breath test result is the functioning of the breath test machine itself. The type of machine will vary from state to state, and from county to county within a given state. 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 accuracy checks, calibration records, usage logs and maintenance history are all properly documented and don’t reveal any problems.

An experienced California DUI defense lawyer will know just how to investigate each area of potential problems. When these problems are revealed, they may result in the breath test results being excluded, or may just be used to attack the weight of the evidence. In either event, a criminal defense DUI / DWI lawyer will know how to use these issues to the driver’s best advantage.


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