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Chemical DUI Testing: Blood, Breath and Urine

Chemical testing is often used by California law enforcement in suspected Driving Under the Influence (DUI) cases, sometimes known as DWI (Driving While Intoxicated). These chemical tests measure the amount of alcohol in a person's system by testing breath or blood; in cases where drugs are suspected, they may test a person's urine. While the information gathered from the results of these tests can be used by prosecutors in a DUI case, the tests can also be challenged by a lawyer well-versed in the law, the science and the processes involved in administering and analyzing these chemical tests.

The Chemical Limits:

Under the laws of the State of California, a blood alcohol Content (BAC) of 0.08% or higher can be used to prosecute adult drivers for DUI. For some, this limit is even lower: 0.04% if operating a commercial vehicle, and only 0.01% for drivers under the age of 21, or already on probation for a previous DUI.

Preliminary Breath Testing:

When the police suspect an individual is driving under the influence of alcohol, they will ask he or she to blow into a handheld breath machine. This is known as a Preliminary Alcohol Screening (PAS) device. This test is voluntary for most drivers; only those already on probation for a DUI, or who are under 21 years of age must take the PAS test. The results of this test are “investigatory,” and cannot generally be used as evidence for a DUI conviction.

This PAS test is part of the field sobriety tests (FSTs), and used by an officer to back up their investigation, showing they had reasonable suspicion of driver intoxication. This investigation is used to justify arrest and later testing at the police department station, where more reliable testing methods can be performed.

DUI Breath and/or Blood Testing:

Once a person has been placed under arrest, they will be taken either to the police station/jail. Breath tests are taken either at the station or jail, while blood tests may be taken at the police station, jail, or in the hospital. Results of these chemical tests are considered to be more accurate in determining a person's blood alcohol content. As with any alcohol level testing, the timing of the test is very important. The test must occur within three hours of the arrest to be considered as evidence of a DUI. The choice of breath or blood is up to the individual, but refusing to consent to either one can lead to additional consequences. (See below)

While very accurate, there are ways to challenge the accuracy of one's BAC levels as determined by either breath or blood testing. Errors can take place, for example, in drawing the blood, in the actual testing of the blood itself, and in the calibration of the machines used to test either one's breath or blood.

DUI Urine Testing:

Generally, when the police suspect an individual of an alcohol related DUI, the breath or blood will be tested. Urine is not usually tested when alcohol is involved or suspected. However, when the police suspect that an individual is driving under the influence of drugs — also considered a DUI — they may demand urine or blood testing. Urine tests generally take place at a hospital or police station. Similar errors may occur when testing urine for drugs as when testing blood, and this needs to be investigated.

DUI Chemical Test Defenses:

The purpose of all the above chemical tests are to obtain evidence that a person was over the legal limit for purposes of a DUI. However, each of these tests has limitations in their testing, and what potential errors could result in a false reading.

  • Human Error:

The above tests rely on machines to analyze the chemicals, but they are operated by humans, and humans make mistakes. Officers are trained in administering, maintaining, and reading breathalyzer tests. But they may misread the findings, or fail to properly operate or calibrate the testing devices.

  • Machine Error:

The testing machines are very sensitive scientific measuring devices. However, these devices need to be properly maintained, operated correctly, and be regularly calibrated to ensure that their readings can be relied upon.

Refusing the Chemical Tests:

While there are limitations to the science and applications for these chemical tests, refusing to take the tests can result in serious additional penalties for both the DMV administrative suspension of your license, and for the DUI criminal court case. Generally, refusing chemical testing will result in a lengthier suspension of your license. In California, if you are lawfully arrested by an officer for probable cause believing you have been driving under the influence, you have “implied consent” to taking a chemical test to determine your BAC.

  • In the Field:

Field breathalyzer tests are generally optional, but not necessarily for drivers under 21 years of age, or for drivers on DUI probation.

  • At the Police Station/Jail:

There are penalties for refusing to submit to chemical testing, which may include driver's license suspension or revocation, fines and/or jail. In California, as in most states, you are required to submit to chemical testing after being arrested for DUI. However, the arresting officer must inform you of this requirement correctly, and give you the choice between testing either your breath or blood.

Experienced DUI Attorney Representation:

Lynn Gorelick has had the same training as law enforcement  in administering and analyzing these chemical tests and testing machines.  She knows how to operate the machines, how to properly calibrate the machines, and what the readings demonstrate from a scientific and legal perspective.

Whether you are arrested in Richmond, El Cerrito, Danville, Walnut Creek, Hayward, Fremont, Oakland, Berkeley, Dublin, or anywhere else in Contra Costa or Alameda County, Lynn Gorelick is familiar with the local DUI laws, and the local officers.  With over 30 years of DUI experience, Lynn Gorelick understands the law and the science required to fight DUI charges.

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We offer a free initial consultation to people accused of DUI and criminal offenses in the Bay Area. Call us at 510-785-1444 to schedule yours.

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