DUI Breath Tests and Breathalyzer Defenses

As we have discussed in other sections of our site, DUI breath tests and breathalyzer defenses exist in all breath DUI cases. Breath machines, like the Alcosensor IV, and Alcosensor V used in Orange County DUI cases, are subject to certain known issues. Those issues can make them less accurate than other testing methods, such as blood, although blood tests have their own defenses based upon separate types of testing problems.

Why police do DUI breath tests

In California, it is both illegal to drive with any substance, in any amount, that impairs your ability to drive safely (i.e., under the influence), and also, under California Vehicle Code VC 23152(b), it is illegal to drive with an amount of a .08% as a percent of your blood, even if you are not impaired, or under the influence. It’s a strict hard limit that exists under the law.

Testing blood may be more accurate in some respects, although there are defenses to blood tests in a DUI and blood testing has its own problems. But under the U.S. Supreme Court ruling in the McNeely case, obtaining blood is so invasive that it either requires a search warrant for blood, or requires the consent of the person to be tested.

Since under California law, police have to obtain a breath or blood test within three hours of driving, getting a search warrant, signed by a judge, at all hours of the night, jeopardizes the blood alcohol results that can be used in a DUI case, based upon timing.

A breath test is simpler, and easier, for police. It allows testing to be done closer to the time of driving, which is the only important time for legal purposes, and doesn’t require a warrant. Just “blow and go”. However, breath tests are considered less accurate than blood testing, overall.

DUI Breath Tests and Breathalyzer Defenses – Mouth Alcohol

Mouth alcohol is a known problem with DUI breath tests. In fact, breath machine manufacturers have redesigned breath tests to try to minimize this interference when testing.

As you can tell from the name, mouth alcohol is alcohol trapped in the mouth. Dental work, which can trap alcohol, food in the teeth, listerine strips, and other alcohol in the mouth can create a higher alcohol reading than what is supposed to be tested – deep lung air.

For that reason, breathalyzer machines have a “slope detector” installed in modern machines, which prevents the measurement of the earlier part of the breath sample, which is from the mouth and upper airways, and tests only the deep lung air. If the BAC value is changing too rapidly, the machine will consider it mouth alcohol, or some other problem, and not accept the sample. For that reason, a breath test needs a longer blow, which many find uncomfortable.

Breath Test Defenses – Radio Interference

With a breath test, the air being blown passes through a mouthpiece, which contains a spit trap. That trap needs to be replaced after every failed test and after every subject uses it. The mouth piece then passes through a heated breath tube. That tube is heated to prevent condensation from forming. The tube also has an antenna that is supposed to check for RFI (Radio frequency interference). If police radios, walkie talkies, or other electronics are near the machine, that can cause it to fail or cause DUI breath tests and breathalyzer defenses based upon inaccuracy.

Breathalyzer Defenses – Margin of Error

No machine is 100% accurate. Officers and personnel from the Department of Safety will often testify the margin of error is as low as .005 or 5%, and as high as .02. Because the margin of error is at least .000001, the State should not always be able to obtain a Per Se conviction on .08, or an aggravated conviction on .16. The reason being that any result is as likely .07999999 as it is .08000001. In fact, California law allows a breath machine to be calibrated within .02% of a true reading. That means that a .08% can be truly as little as a .06%, or as high as a .10%, and still be considered accurate.

By law, each breath sample must be within .02 of each other. This makes for the .02 margin of error. The error rate to confirm an independent sample is even higher; as much as .05. That can make a huge difference in a low blood alcohol case.

DUI Breath Defenses – Temperature

The temperature of your Mouth, and the temperature of the Body, as well as outside (atmosphere) temperature, also affects the results of the breath machine. The reason for this is based upon how DUI Breath Tests and Breathalyzer Defenses work. The breath testing device works using Henry’s Law (which states that the concentration of a solute gas in a solution is directly proportional to the partial pressure of that gas above the solution). “The value of the Henry’s law constant is found to be temperature dependent. The value generally increases with increasing temperature. As a consequence, the solubility of gases generally decreases with increasing temperature.”

Breathalyzers assume a sample of 34 degrees Celsius. In fact, the simulator temperature must be within +/- .2 of that temperature. You can see what the actual temperature was by looking at the printout reading issued by the breath machine.

The problem with this temperature is that everyone’s breath is different, and the average tends to be closer to 35 degrees. For every one degree difference, there is an 8.6% overestimation of BAC.

Having a fever, or going through a regular woman’s menstrual cycle/menopause, can give higher than average body temperatures. Arguably, if someone is stressed, such as due to an arrest, their body temperature will also rise. When the body’s fight/ flight system is activated, muscles tense, heart rate and vital organs speed up and as a result, blood flow is shunted from the extremities and directed to the vital organs to facilitate the increased level of arousal. As a result, changes of 5°, 10°, or even 15 degrees can occur within just a few minutes. If an officer says the person has a flushed face, you may also be able to argue an increase in body temperature.

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Contact us today. If you have the need for a top DUI defense attorney in Orange county, contact us for a free evaluation of your case, and how breath testing defenses can help you. We are happy to help.