Contesting Breath Alcohol Tests with Partition Ratios

DUI breath tests are standard tools used to prove someone was driving under the influence of alcohol in California. However, breathalyzer tests are not always accurate. Furthermore, the breathalyzer does not measure the amount of alcohol in your bloodstream, so there is the opportunity to contest the accuracy with partition ratios.

How Does a Breath Test Work for a California DUI?

Police officers use two types of breath tests to determine if a driver was intoxicated while driving. First, the roadside preliminary alcohol screening (PAS) test is a roadside breathalyzer. It is given during a DUI stop and investigation.

You can refuse the PAS test without penalty unless you are under 21 years of age or on DUI probation. You can also refuse to take a cheek swab or perform the field sobriety tests too. However, you cannot refuse the second breath test without penalty.

The second breath test is a post-arrest evidentiary breath test. You cannot refuse a chemical BAC test after your arrest without penalty. These are evidentiary tests, meaning the state can use the results in court. 

Most drivers choose between the post-arrest breath test and the blood test. However, the person may be required to take a blood test if the officers believe they have drugs in their system (DUID), they cannot blow hard enough for the breath test, or the driver is unconscious or in a medical facility where a breath test is not available. 

How Does a Breathalyzer Test Work?

Understanding how to challenge the results of a breath alcohol test using partition ratios in California helps to understand how breath tests work. DUI breath tests do not measure the blood alcohol level in your bloodstream. Instead, they measure the amount of alcohol in the deep lung air.

Deep lung air comes from the alveoli located deep within the lungs. Tiny blood vessels surround the alveoli. The blood vessels allow oxygen to pass from the lungs into the bloodstream and allow carbon dioxide and other substances, like alcohol, to pass from the blood to the alveoli. 

The alcohol concentration is highest in the alveoli. Therefore, an evidentiary breath test uses the air from this area to test for alcohol in your system. However, you must blow very hard to get the air from the alveoli into the machine. Some individuals may not be able to blow hard enough and might need a blood test.

How Can the Partition Ratio Lead to Inaccurate BAC Levels?

Since the breath test measures the amount of alcohol in your lungs, the results must be converted to a rough equivalent of a BAC. The mathematical conversion is known as the partition ratio. 

California laws set the partition ratio for breath-testing at 2,100 to 1. In other words, the amount of alcohol in 2,100 milliliters of breath is equal to the amount of alcohol in 1 milliliter of blood.

However, everyone’s body is unique. Your partition ratio may differ from the fixed partition rate because everyone’s lungs absorb the alcohol at a different rate. 

How Does the Partition Ratio Impact a DUI Case?

Under California Vehicle Code §23152, it is unlawful for you to operate a motor vehicle if:

  • Your BAC is .08% or higher (per se charge) OR
  • You are under the influence of any alcoholic beverage (generic dui charge)

A per se DUI is where the person’s BAC is .08% or higher. The law presumes that you were too drunk to drive if you have a BAC over the legal limit. Therefore, if your breath test shows a BAC of .08% or higher, you are presumed to be too impaired to operate a motor vehicle.

However, if your BAC is below the legal limit, you are charged with a generic DUI. The prosecution must show that the alcohol in your system actually impaired your ability to operate the motor vehicle safely. In cases with BAC close to the legal limit, the prosecutor might get a conviction if there is other evidence the driver was intoxicated. 

On the other hand, if the person’s partition rate is not 2,100:1, the person’s BAC level might be much lower than the level alleged by the prosecution. If so, the person may not have been impaired by alcohol when they were pulled over for a DUI stop.

Challenging the Results of a BAC Level Using Partition Ratios

In July 2009, the California Supreme Court decided an important case that changed how some people defend themselves against the generic DUI charge. The decision in People v. McNeal allows a defendant to contest the accuracy of a breath test by submitting evidence their partition ratios are not equal to the ratio set by law. Defendants may also challenge the results by offering evidence proving the variance of partition ratios among the general public. 

In a borderline BAC case, offering evidence that the defendant’s individual partition ratio is different from the state’s ratio could create reasonable doubt for the jury. Especially when there is no substantial evidence other than the breath test that proves the defendant was intoxicated while driving.

If your DUI case relies on the results of a breath test, talk with a California DUI defense lawyer before accepting a plea deal. You may have grounds for challenging the results to prove you were not drunk while driving. 

Other Ways to Challenge an Evidentiary Breath Test in a DUI Case

In addition to challenging the accuracy of the breath test results based on partition ratios, there are other ways to attack a breath test. For example, the California Code of Regulations Title 17 sets the rules for DUI chemical testing procedures. As a result, the samples could be invalid when labs and law enforcement officers do not follow these rules.

There are many rules under Title 17 for performing a breathalyzer test after a DUI arrest. Some important rules include:

  • The device must be calibrated every 150 uses or ten days, whichever comes first
  • The person giving the breathalyzer test must be trained to use the specific device
  • The DUI breathalyzer device must be in good working order
  • Air from deep within the lungs must be collected to perform the test
  • The driver must be watched continuously for 15 minutes before the DUI breath test to ensure they did not eat, drink, or put anything in their mouth, smoke, vomit, burp, or regurgitate
  • The lab must keep detailed records of the personnel, equipment calibration, and test results
  • Two breath samples do not differ by more than 0.02 grams per 100 milliliters of blood must be obtained

Violation of any of the above Title 17 rules could result in inaccurate BAC levels that are not as high as they appear. A DUI defense lawyer reviews the testing procedures and records to determine if the lab or law enforcement agency made errors that could support a challenge to the breath test results.

Medical Conditions and Other Factors Could Result in Incorrect BAC Breath Test Results

In addition to problems with the machine and errors made by law enforcement agents or lab workers, a person’s medical conditions could affect the accuracy of a breath test. Specific health conditions can result in falsely high BAC levels. 

Examples of medical conditions or other factors that could affect the BAC results from a breathalyzer include: 

  • Diabetes
  • Gastrointestinal reflux disease (GERD)
  • Low carb/high protein diets
  • Residual mouth alcohol
  • Inhaling acetone and other volatile chemicals
  • Rising blood alcohol levels
  • Medication, food, or mouthwash caused a false high
  • Dentures caused the alcohol to pool in the mouth

There are many ways to challenge an evidentiary breath test. It is worthwhile, especially in cases where the BAC level may be just below the legal limit. Challenging the accuracy of the test can help jurors accept your argument that you might have had some alcohol, but you were not impaired to drive.

What Should I Do After a DUI Arrest in California?

Do not panic. You have not been convicted of driving under the influence. However, the matter is extremely serious. The punishments for a DUI conviction in California can be harsh.

Therefore, do not talk to the police. The police officers and the prosecutor already believe you are guilty. Any information you give them only makes their case against you stronger.

Instead, remain quiet until you speak with a California DUI defense attorney. Your attorney discusses the facts of your case, your legal rights, potential defenses, and the best options you have for fighting the DUI charges. 

You might want to fight the drunk driving charges based on your attorney’s advice. You might have a solid challenge to the evidentiary breath test results based on partition ratios or errors regarding the test. 

If not, your attorney works to negotiate the best plea bargain possible. A prosecutor may be willing to work out a better deal with an attorney than directly with you. 

The prosecutor knows if a deal is not struck, the case goes to trial. That might not be in the prosecutor’s best interest. Furthermore, the prosecutor has hundreds of cases to handle. They want a win, not a hard fight for a potential acquittal.

Ensure you know your legal rights after a DUI arrest to reduce the chance of jail time and other penalties.

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