What Really Happens with a DUI Breath Test

If you were arrested for a DUI in California, chances are that you gave a breath test.  (Sadly, even though law enforcement officers are supposed to give arrestees the choice of a breath or blood test when arresting for DUI alcohol, or the choice of a blood or urine test if arresting for DUI drugs, oftentimes this obligation is ignored and people end up taking the test that the officer chooses for them.) Many people believe (erroneously) that if the machine says that they were above the legal limit, then they are guilty, and conviction and punishment are inevitable.  Thankfully, that’s not the case.

First, it is important to recognize that in California, the crime is defined as driving under the influence, or driving with a blood or breath alcohol level of .08 or higher. Thus, the critical moment is what I like to call the “Oh crap!” moment, when the driver was last driving, and looked up in the rear-view mirror to see the red and blue police lights flashing.  That is the time it is illegal to be under the influence, or have a breath alcohol level of .08 or higher. It is not illegal to have a breath test result that is above the legal limit an hour later when you are back at the police station; in fact, that breath test result taken at the station is only relevant to the extent that it allows someone to look back and determine what the alcohol level would have been at the time of driving.

Next, there are many requirements that must be observed in order to have a valid and admissible breath test.  Many of the regulations are found in Title 17 of the California Code of Regulations.  Still others are developed by court decisions.  If the legal predicates aren’t followed, the breath test results may be inadmissible, or arguments can be made that little weight should be given to the results.

There are two types of DUI breath testing that are done in California:

•    the pre-arrest screening breath test, and
•    the post-arrest “evidential” breath test.

There are different requirements as to each.  Further adding to the nuanced area of breath testing is that there are two different technologies that may be used in these devices.  Some are “fuel cell” breath testing machines; others use  “infrared” technology. There are attacks to be made against both of these.

The pre-arrest screening test (sometimes referred to as a PAS device – an acronym for Preliminary Alcohol Screening) is a hand-held device, a little bit bigger than an iPhone, and this device is usually used at roadside, most typically just after the physical field sobriety tests are concluded.  The PAS test is, by definition, another field sobriety test, and the purpose of the PAS device is to further justify the decision to arrest. (In fact, the numeric results from this roadside breath test used to be considered too unreliable to be admitted into evidence.)  The core technology in the PAS test is the “fuel cell”, and carries with it a host of problems.

The post-arrest evidential test may also be done on a fuel-cell machine, an infrared machine, or a machine that combines both of these.  Regardless of which is used, they are all susceptible to attack. Adding to the complexity, and sometimes confusion, is that some of the post-arrest evidential machines can be administered at the side of the road.  Others are done back at the police station.

Regardless of what technology drives the machine, and regardless of where the test is administered, there are many ways to raise doubts about the reliability of the results.
Some challenges relate to the machine itself.  Others concern the operator.  Still others relate to whether or not the subject is a suitable candidate for breath testing.  There are also issues related to timing and “retrograde extrapolation”, since the crime of DUI relates to the driver’s condition at the time of driving, as contrasted with the later time of testing.

•    Machine issues: disconnect between what the breath machine says, and observed symptoms showing lack of impairment; Radio Frequency Interference that can be brought on by nearby cell phones, computers, other devices being plugged into common circuits, and more;

•    Operator issues: Officer operating breath machine cannot explain theory and operation of breath testing as required by law; Officer fails to follow test manual protocol; insufficient or improper observation period prior to testing;

•    Arrestee inappropriate subject for breath testing issues: Physical problems like emphysema, gastro esophageal reflux disease (GERD), persistent heartburn; false teeth, food pockets, gingivitis, or other dental issues that cause alcohol to trapped in the mouth; exposure to chemicals that can be misread by the machine as “alcohol”; decreased lung volume; “Tyndall” effect, following the deployment of air bags;

•    Timing issues: this requires analysis of what the subject ate and drank, and when they ate and drank it, since alcohol levels change over time.  It is quite possible for a subject to have been below the legal limit at the time of driving, only to have their alcohol level rise at the later time of testing.

Breath testing is an exceptionally complex area, there are many ways it can be demonstrated to be inaccurate.