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False PAS Readings

Imagine you are driving through the East Bay when you suddenly see police lights behind you. You pull over to the side of the road, wondering what it was you were doing wrong. An Oakland Police Department officer approaches your window, as you ready your license and registration. The officer asks if you've been drinking tonight, and you respond “no.” The officer asks you to take a Preliminary Alcohol Screening test (PAS) -- what some people call a “breathalyzer test” -- and since you haven't been drinking, you agree. You blow into the device, and the next thing you know, you are placed under arrest for driving under the influence (DUI).

How is this possible? How could you blow a positive reading on a PAS machine when you weren't drinking alcohol? Or how could you test above the limit if you only had one beer? It may be surprising for most people to learn that field breathalyzers are not entirely accurate, and there are a number of things that can give false positive results.

Chemical Breath Test in the Field, or PAS Test

If you are pulled over by the police and they suspect you may be under the influence of alcohol, they will ask you to take a PAS test. A PAS machine is a field device intended to test the level of your blood alcohol concentration (BAC). These field devices are not as accurate as the breath test machines at the police station.  In part, for this reason, PAS results are not always used as evidence, but are explained by the police as an investigative tool which may lead police to place you under arrest for driving under the influence (DUI). But just how accurate are these tests, and what else can set them off, other than alcohol?

Alcohol in Breath

When alcohol is consumed, it finds its way into the bloodstream. As the blood flows through the body, and across membranes in the lungs, some of the alcohol evaporates into the air in the lungs.  The concentration of alcohol in the lungs is related to the concentration of alcohol in a person's blood. The more alcohol in the blood, the more alcohol in the air in the lungs. This ratio is 2,100 to 1. So 2,100 milliliters of air in the lungs will have the same concentration of alcohol as 1 milliliter of blood. Testing the amount of alcohol in the lungs will give a reading which correlates to the BAC.

How the Breath Test Works

Breath alcohol testing devices were first developed in the 1940s. In 1954, the “breathalyzer” was invented, and became the first practical device to test roadside BAC. Robert F. Borkenstein, who began his career as a police officer in Indiana, is responsible for inventing the device which uses breath samples to test blood alcohol levels.

The breath test involves a chemical reaction with alcohol, which creates a testable color change in the device. It contains a tube, which a user blows air into, and a sample chamber which holds the air. Two vials contain the chemical reaction mixture and photocells measure the color change resulting from the chemical reaction.

Air is blown through sulfuric acid, which transfers the alcohol into a liquid solution. The alcohol reacts with potassium dichromate, to change colors. The level of color change is related to the concentration of alcohol in the breath. The color change level is compared to an unexposed mixture, which creates an electric current in the photocell system. This is translated into a measure of blood alcohol concentration.

False Positives from Medications

Any number of things can yield a positive BAC reading, aside from beer, wine, or liquor. Many medications contain some form of alcohol, which can be enough to result in a PAS reading high enough to cause the officer to suspect Driving Under the Influence.

Anbesol is a popular oral pain relief gel, used to treat toothaches, canker sores, and cold sores. The gel is applied topically to areas of the mouth. Anbesol's primary ingredient is benzyl alcohol, which can produce a positive BAC reading.

Cold Medicine, such as Contac Severe Cold, Formula 44D, and Nyquil all have 20% alcohol or more as a primary ingredient. Even if you're taking cold medicine to relieve a cough or other symptoms, you may inadvertently test positive on a PAS device.

Cough Drops are small, and while they do not contain large amounts of alcohol, if they were used shortly before taking a PAS test, they may give an artificially elevated blood alcohol reading.

Asthma Inhalers, such as Albuterol contain methyl group chemicals, which can also show up the same way as alcohol in a PAS test. In addition, many inhalers contain alcohol as a propellant, which can also affect readings.

Other False Positives

Breath tests are intended to read lung alcohol levels, but alcohol in the mouth can skew BAC results. For this reason, police officers wait for 15 minutes or more, observing a suspect, before administering a station breath test. This is intended to limit the impact of mouth alcohol, or the effect of other substances affecting the breath test.

Burping or Acid Reflux can bring some stomach contents up the esophagus and into the mouth.  If there is alcohol in the stomach, this can bring up levels of alcohol in the mouth, creating a higher BAC reading that the actual blood BAC level.

Low Blood Sugar, also known as hypoglycemia, can cause acetone to be present in the breath. For many people, hypoglycemia comes from having diabetes. For these people, the levels of acetone in the breath can impact PAS readings.

Mouthwash and breath sprays have high levels of alcohol. Using mouthwash shortly before taking a breath test can result in a false BAC reading due to the amount of alcohol remaining in the mouth.

Chewing Gum can have ingredients like xylitol or sorbitol, which are known as sugar alcohols.  Although chewing the gum won't get you drunk, it can affect the results of a breath test, to make it appear that you were drinking.

Improper Calibration

Breath testing devices, whether used in the field or back at the station, are imperfect, to say the least. In addition to not being 100% accurate, they need to be regularly calibrated to assure some level of accuracy. If breath machines are not calibrated properly and in a timely manner, they can yield false readings.

Arrested on Improper Results

Whatever you think the reason may be for an improper breath test reading, police officers are not interested in hearing your explanation.  They will simply place you under arrest, take you to the police station, and impound your car.  You may need to wait until you are released from custody to find any sort of relief.  The best option is to seek out a qualified, local DUI attorney.

An experience DUI lawyer has the knowledge and understanding of what can set off the breath test, and what can give improper readings. Highly trained DUI attorneys know the science behind chemical testing, how to calibrate breath test machines, and how police are supposed to administer chemical tests. Most importantly, a skilled DUI lawyer can use their legal knowledge in conjunction to get breath tests thrown out, leaving the prosecution with no case against you.

Experienced DUI Attorney Representation:

Whether you are arrested for a DUI in Fremont, Oakland, Berkeley, Dublin, or anywhere else in Contra Costa or Alameda counties, Lynn Gorelick is familiar with the local drunk driving and DUI laws.  She knows the local prosecutors, judges, and officers involved.  With over 30 years of DUI experience, Lynn Gorelick understands the law and the science required to fight DUI, and other alcohol charges.

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