Being under suspicion for drunk driving in California does not warrant an arrest. Law enforcement officers have to be sure that you were driving under the influence first, which they achieve through DUI breath tests or sobriety tests. The result of these tests will show how high your Blood Alcohol Content was at the time of the arrest. The results will be used as evidence against you in a criminal court.

DUI is a grave offense in California. For that reason, it is good to ensure that your test results are accurate to avoid facing charges for a crime you have not committed. It starts with an in-depth understanding of what these tests are, how they are administered, and factors that could affect your results. At the Orange County DUI Defense Attorney Law Firm, we are available to answer all your questions regarding breath tests for DUI. If, therefore, you are facing arrest in Orange County for DUI, get in touch with us today.

Understanding DUI Breath Tests and When They Are Needed

There are two main ways in which a person can manifest drunk driving:

  • In the way that they are operating their vehicle
  • In the amount of alcohol in their blood

These two are the primary basis of DUI charges in the state of California.

When it comes to a motorist’s behavior on the road, the court will want to hear such evidence as reckless driving, speeding, and disregard for traffic rules, among other things. However, to collect evidence on how much alcohol is in a person’s blood, DUI tests have to be conducted. Among the most popular DUI tests are California breath tests.

The state of California advocates for two DUI testing approaches. Both of them are administered in two stages, as will be explained here.

  • The first stage will be the initial roadside screening for alcohol content in the blood, done through a PAS test. This test is administered during a DUI stop and inquiry in California.
  • The second test is the post-arrest test, done to gather further evidence on DUI. This test is administered through desktop equipment either at a police station, in a mobile police unit, or sobriety

PAS Testing

The PAS testing occurs as soon as you are under suspicion for drunk driving, to kick-start the DUI investigation. When a traffic officer pulls you over on suspicion of drunk driving at a state DUI checkpoint, they are required to conduct a test on you to be sure that you are indeed operating a vehicle under the influence. The police do this before they make an arrest. 

A PAS test will be administered by the use of a hand-held device, for instance, a Breathalyzer. The test is not conducted on all drivers, and it is okay for a driver to decline taking it. Some of the drivers that are not exempted from taking the PAS test include:

  • Those who are on probation for DUI
  • Drivers who are below the age of twenty-one and are, at that time, under investigation for a DUI-related offense according to California’s Zero Tolerance Act, which prohibits alcohol consumption or underage driving

If the DUI suspect is in any of the above categories and they decline to take the PAS test, their refusal will be considered as failing to submit to a California chemical test. Refusing to submit to testing is prohibited and could cause a mandatory suspension of the driver’s license, even if the driver will not get a conviction for DUI.

Note that PAS testing is considered field sobriety testing and is used mainly to help the traffic officers decide whether or not they will arrest a driver for drunk driving. Any other person, other than those in the categories provided above, is free to take or not take the PAS test. If you refuse to submit to this test, you will not face any penalties.

Evidentiary Post-arrest Testing

The evidentiary post-arrest testing, on the other hand, is a mandatory chemical test that any motorist who has been legally arrested for drunk driving must take in California. The motorist must take the test even though he/she did not submit to the preliminary testing. Sometimes the police allow drivers to choose between a blood and breath test. There are exceptions to this though, for instance:

  • If the officers genuinely believe that the motorist was operating a vehicle under the effects of drugs. If that is the case, the driver will be required to undergo a blood test
  • If the motorist is not able to strongly blow when taking a breath test
  • If the motorist is dead or unconscious
  • If the driver was unwell and was sent to a healthcare center where a breath test device was not available

Are DUI Breath Tests Optional?

As mentioned above, the post-arrest test is mandatory. It means that failing to submit to the test will have legal consequences. Some of the effects could be:

  • Driver's license suspension for a minimum period of one year
  • If the driver gets a DUI conviction in the end, they receive a mandatory sentence improvement of forty-eight hours in jail

Note that a person can decline to submit to a post-arrest breath testing if they have opted for blood testing. What matters is that their blood-alcohol content level is determined, as this is what will be used as evidence in court during their DUI hearing.

If the driver had refused to submit to a DUI test and is later convicted in court for the offense, California courts may allow him/her to continue operating their vehicle but with a restricted license. If the driver agrees to have an IID installed in their car, they may be able to drive anywhere without any restrictions.

A Blood Test or Breath Test

DUI attorneys in California will advise you to take either of the two tests. However, the tests are different in one way or another. First, breath tests are preferred because they are quick to administer and are not invasive. The problem with breath tests is that they are subject to many errors and could give the wrong result. If you happen to get a higher BAC result than what you had at the time the test was taken, you might face hefty charges for drunk driving even though there are chances that the result was at the standard level or below. 

Blood tests, on the other hand, will require a sample of blood drawn from the defendant. The sample will then be tested to show the amount of alcohol in his/her blood. A sample can even be saved for the defendant or their attorney to conduct an independent test later on. It ensures that the criminal court only admits the correct reading. Breath samples, unlike blood samples, cannot be preserved for testing. Therefore, those who choose to take the breath test have no way of ascertaining that only the correct result is used in court.

California Title 17 Code and its DUI Implications

California Title 17 is a Code of Regulations that provides several rules regarding how the following should be conducted in California:

  • Breath tests for DUI
  • Blood tests for DUI
  • Urine tests for DUI

The three are the chemical tests used to gather evidence against a driver who is under suspicion for drunk driving. The prosecutor uses the results of those tests to support the charges the driver might be facing for driving under the influence. However, in gathering this evidence, the police must comply with Title 17. If not, the prosecutor will not be able to use the results of those tests as evidence in court.

What this means is that Title 17 could be the basis on which a successful defense strategy for DUI cases can be built. Any violation of Title 17 by the police while gathering evidence can result in the court dropping the defendant’s charges. The defendant’s attorney could also take advantage of that violation to bargain for lesser charges.

Title 17 is the Code of Regulations that governs how DUI testing procedures should be conducted. Some regulations must be adhered to by both the police and the laboratories where these tests are conducted. There are regulations for both the collection and processing of samples for DUI testing. If any person does not adhere to the procedures provided in Title 17,  it could lead to a compromise in BAC results.

California law under Penal Code 1538.5 allows a person to petition the court to exclude specific evidence if he/she reasonably believes that the evidence has been compromised. If the judge agrees to the request, the compromised DUI test outcomes will be inadmissible in a criminal court. What this means is that there will not be any proof to show that the motorist was indeed driving under the effects of drugs or alcohol. This is how most DUI cases end up getting dismissed in courts.

The most crucial testing regulations provided under Title 17

Title 17 contains many rules regarding chemical tests. The most significant of them are:

  • That the device used for DUI breath tests must always be in excellent working condition
  • That calibration of the equipment should be at least every ten days or after 150 uses, one of the two that comes first
  • That the person who will be administering the test should be well-trained on the use of the exact device, they will be using
  • That the motorist must be kept under continuous observation every fifteen minutes before the testing is conducted. During that time, the driver must not eat, smoke or drink anything, put anything in their mouth, must not regurgitate, vomit or burp as these will leave more alcohol in their mouth than there previously was
  • That the person operating the breath testing device should aim for the air that is rooted in the defendant’s lungs
  • That the operator should obtain two samples whose results must not differ significantly. It means that the defendant will have to give two blows for the operator to collect two samples
  • The laboratory that is conducting the sample analysis should have a detailed record of the device calibration, the operator, and the test results.

Some of the Violations of Title 17 that Could Result in False Blood-alcohol Results

Violating Title 17 can consequently lead to false BAC readings. Some of the violations that could cause a false reading include:

  • If the testing device wasn’t tried or well calibrated
  • If the operator made an error while taking the breath samples
  • If the operator did not keep records of the test results as mandated by law

Attorneys working in defense of those facing DUI charges will do their best to point out any violation, which could have their client’s BAC results thrown out of the court. An experienced attorney is, for instance, able to obtain both the lab and police records to find out any errors that could help their client’s case. Some of the things he/she will be checking out include:

  • Whether or not the driver’s mouth was empty at the time of testing
  • Whether or not the operator waited for a minimum of fifteen minutes before conducting the test
  • Whether or not he/she attached the device’s mouth correctly to the machine
  • Are there records to show the time the fifteen-minute observation time started?
  • There should be recorded time for every blow that was made, too

How are DUI Breath Tests Taken?

DUI breath tests are conducted in a specific manner, which is the reason why Title 17 calls for training for an operator to be allowed to perform such tests. The main requirement is to aim for the deep lung air, which helps measure the level of alcohol in the defendant's alveolar. Human alveoli are sacs that resemble a balloon that is located deep into the lungs and is surrounded by blood capillaries.

The capillaries are the small blood vessels that allow oxygen to pass from the human lungs to the blood. Capillaries also allow carbon dioxide, as well as other body wastes like alcohol, to move from the blood to the alveoli. This is the reason why California law demands that breath samples for BAC testing be a composition of alveolar.

When a person exhales, they first do so from the mouth or the nasal area, then from their throat and the upper airway, and lastly from the lungs. Since alveolar is in the farthest part of the lungs, its air is usually the last to escape the lungs. Note that this is also the part where the concentration of alcohol is at its highest. The police have to aim for the alveolar air to obtain the best results. That is why the defendant is needed to blow strongly to the testing device during the testing.

However, not all people can blow hard into the testing device, and this could give unreliable test results. Older people, as well as those that have severe medical disorders that affect their lungs, are some of the people who may not be able to give the alveolar air for DUI testing

California DUI Breath Tests and Partition Ratios

When it comes to California DUI tests, only blood tests can provide direct BAC results. Breath tests will not give a direct result, and the result has to be converted mathematically to an amount that is approximately equivalent to a BAC result. This conversion factor is what is referred to as partition ratio. The ratio reflects the connection between the alcohol in the defendant’s blood and one that was measured in his/her breath.

In the state of California, this partition ratio for DUI breath testing devices is set at 2100:1. It means that the alcohol amount in 2100 ml of breath (equivalent to 210 liters) will be taken to be equal to the level of alcohol in 1 ml of blood.

Even though this method is widely used to determine a driver’s BAC level in California, the partition ratio is not always 100% guaranteed, and it could result in inaccurate results. The California law uses a fixed partition ratio, but in the real sense, everyone’s lugs assimilate alcohol from their blood at very different rates. What this means is that the actual partition ratios vary greatly as well, both for individuals at varying times and for the general population.

This, too, is an issue that can help a DUI defendant fight their charges in a California court. If you are facing DUI charges under California Vehicle Code 23152(a), the prosecutor will be required to provide proof that you were indeed impaired while driving. If there was no such evidence as traffic violations, speeding, or any other physical symptoms of intoxication, this might not be easy to prove. If your attorney brings in the argument of a possibility of inaccurate BAC results, your charges may be dropped or reduced.

Other Factors That Affect DUI Breath Tests Results

Other than Title 17 violation and an inaccurate partitioning ratio among other factors named above, several other factors can affect a person’s DUI breath testing results. These are, for instance, a driver's diet and wellbeing. There are medical conditions as well as foods that might trick a breath testing device into providing an inaccurate reading. These are, for instance:

  • GERD
  • A high protein diet or a low carb diet
  • Diabetes

For that reason, it is advisable for anyone with these conditions or is in any of these diets to inform their defense attorney even though it may not seem relevant at that time. A skilled and experienced attorney will know how those medical conditions and diets can help in your defense. It could also be a key to preventing an innocent motorist from being convicted of a DUI because of a false DUI result.


GERD, acid reflux, and heartburn are serious digestive conditions that are likely to produce high BAC results even when a person has not consumed any alcohol. If you have any of these conditions, the contents of your stomach can sometimes move back to your mouth. DUI breath testing devices could read the acid that comes from your belly as alcohol.

Low Carb or High Protein Diets

Low carb or high protein diets, too, have a similar effect, and these are, for instance, Whole 30, Atkins, Zone, and South Beach diets. When a person is in any of these diets, their body is forced to use up the stored fat for energy in place of glucose. The result is a by-product called ketones, whose chemical composition is similar to that of acetone. Most devices used to take DUI breath tests are not able to distinguish between ethyl alcohol that is present in alcoholic drinks and acetone. This causes the device to read ketones on one’s blood as alcohol.


Diabetes, too, can elevate one’s BAC readings during DUI breath testing. It is because the liver of a diabetic person produces ketones, which, as mentioned above, has the same chemical composition as acetone.  People with diabetes are unable to produce insulin, a hormone that helps their bodies burn glucose for energy. As a result, their body uses up stored fat for fuel that causes more ketones in their blood.

Residual Alcohol in the Mouth

Residual alcohol in the mouth can also trick the breathalyzer into providing a false BAC result. This happens if you had previously consumed an alcoholic drink, and some alcohol remained in your mouth’s mucosal lining. When this happens, the breath you blow into the breathalyzer picks up the alcohol in the mouth, causing it to read positive for BAC. Note that after alcohol consumption, the residual in the mouth can remain there for about 15 to 20 minutes. Even if the amount you consumed is little, it will still be read into the sample, affecting the results.

Other than the consumption of alcoholic beverages, other things could cause alcohol residuals in a person's mouth. These are, for instance:

  • Cough syrups
  • Breath sprays and mouthwashes containing alcohol

Find an Orange County DUI Lawyer Near Me

If you have been arrested and are facing charges for a DUI after taking a California drunk driving breath test, it is advisable to speak to an experienced DUI defense attorney. At Orange County DUI Defense Attorney Law Firm, we have a dedicated team that is well-informed about DUI breath testing and how inaccurate the results can be. Call us at 714-740-7866 and let us help you get the justice you deserve.