Breath tests are the single most common chemical test used in DUI cases. They are used more often than blood tests or urine tests, largely because the equipment is readily available and no laboratory test is needed.
California has an “implied consent” law for chemical tests. This law says that if you are arrested for DUI and police want you to take a breath test, you have agreed in advance to take it. Your consent is a condition of driving on California’s roads.
If you refuse the test, you will face penalties.
What is a PAS and is it different from a regular breath test?
Technically, there are two types of breath tests you could be asked to take in your DUI case: the PAS test (preliminary alcohol screening) and the formal breath test. The difference is:
- A PAS is given on the roadside, before you are arrested. The formal breath test is given at the police station after your arrest.
- In most cases, you are allowed to refuse a PAS test. But it is illegal to refuse a breath test once you’ve been arrested. (You cannot refuse the PAS if you are under 21 or if you’re already on DUI probation, however.)
- The PAS test is a small portable unit, whereas the formal breath test usually involves a more rigorous device.
- The PAS results tend to be less reliable and more prone to officer error, although both types of breath test can be challenged.
How does a DUI blood test work?
There are several steps to a breath test:
- The officer who gives you the blood test must be properly trained on the equipment. They must also follow a large number of rules and regulations to make sure they are getting an accurate reading. This includes properly calibrating the machine on a regular schedule to ensure the results are not skewed.
- If you have already been arrested for DUI, officers will first tell you that you are required to take the test by law and that there are penalties if you refuse. They will then ask if you agree to the test. If you don’t cooperate, or you delay in any way, you will be charged with refusal which adds more jail time, license suspension time, and DUI school to your sentence if convicted.
- You are allowed to request a different type of test, however, such as a blood test or urine test. If this other test is not available, you must take the breath test.
- Before the test, officers must perform a 15-minute “observation period.” During this time they should watch to see that you do not burp, vomit, or eat or drink anything. This is to ensure that there is no mouth alcohol that contaminates your breath.
- Officers will then have you blow into a tube attached to the device. You need to blow air from deep in the lungs for several long seconds for the machine to get a reading. If you do not blow hard enough or properly, it may count as refusal. You should tell police if you have a medical condition that makes this difficult, such as asthma. This does not count as “refusal” and they should give you a different kind of test.
The machine will immediately analyze the amount of alcohol in your breath and record this number, which it converts to an estimated blood alcohol concentration (BAC). The data is recorded, but the breath sample itself is not stored, and cannot be re-tested.
Are DUI breath tests reliable?
Frankly, no, they are very inconsistent. The science behind the test is sound, and under ideal conditions the test does give a reliable estimate of BAC. Unfortunately, conditions are often far from ideal. Some of the most common problems we see with DUI breath tests are:
- Testing device was not calibrated according to schedule
- Driver was wrongly told that the roadside PAS test is required, not optional
- Driver was not informed that the formal breath test is required, or wasn’t informed of the penalties
- Police wait too long to do the test, allowing BAC levels to rise
- Police do not follow the 15-minute observation period
- The operator does not use the device properly
- The machine gives a false reading because of GERD, diabetes, diet, or mouth alcohol
Any of these factors can result in a BAC reading that does not match your actual blood alcohol levels. These mistakes can make a sober person look drunk, or they can push you above the .08% “legal limit” when really you were below it.
Can I have a lawyer challenge the DUI breath test?
Yes. A good DUI lawyer will understand how to challenge the test results on any of the grounds above, as well as for other reasons. You lawyer will also know how to pull the information you need to make the court take this challenge seriously—such as data from the breath test device itself, records about its calibration schedule, and officer reports on how the test was conducted. If there was a breach of any of the guidelines for conducting a breath test, it could mean that the judge will suppress the test results. This puts the prosecutor in the very difficult position of trying to prove you were intoxicated with absolutely no evidence of your blood alcohol level. This is often when you will be offered a much better deal, such as reducing the DUI to a minor charge.
In other cases, your lawyer could find out that the traffic stop or arrest itself was illegal, which can make the breath test irrelevant.
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