Portable Breath Test (PBT) machines are popular with police because they are .. well.. portable. And quick. The problem is that these machines register not only for ethanol (the alcohol found in alcoholic drinks) but also for several other types of alcohol, such as isopropanol. So, for instance, if you are a diabetic who hasn’t eaten within the last several hours and you blow into the PBT machine, you will have isopropanol in your system, caused by the diabetes, but will register as over the limit according to the PBT. If you have eaten sorbitol, an artificial sweetener, or yeast bread, which can break down into ethanol, again, you may register as over the limit according to the PBT but not be actually intoxicated.

Residual Mouth Alcohol – The PBT machine operates on the assumption that the subject has no residual mouth alcohol. When this is not a valid assumption – as it often is NOT – the results can be greatly skewed against the defendant. The fact is that alcohol is retained in the mouth for some time after you drink which can falsely elevate the alcohol reading. (Experts are not agreed on exactly how long but everyone agrees at least 15 minutes.) And besides alcohol there are many other sources of residual mouth alcohol which can also contribute to a falsely elevated reading, such as reflux disorders and breath fresheners. But PBT machines have no way to detect residual alcohol in the mouth and distinguish it from alcohol in the breath – which is what shows the true level of intoxication.

Portable Breath Test and 15 Minute Observation Period

DWI15 Minute Observation Period at Scene vs. Station – This problem of residual mouth alcohol and PBT’s is why police are required to conduct a 15 minute observation period before giving you the “real” breath test at the police station – the one that can be used against you in court – with the clunky Intoxilyzer 5000 EN. At the roadside, this observation period is not required and this means that your breath sample on the PBT may not be only deep lung air – (which it should be) – but will probably also contain residual mouth alcohol and skew your results.

For a breath test to be valid, the officer must observe the defendant for at least 15 minutes prior to the test. This does not include the break in the observation when the officer gets out of his squad car at the station to retrieve the arrested citizen. Therefore we obtain the dispatch records and the mobile data terminal records to determine the exact time the officer arrived at the station and may have started the 15 minute observation period after getting the defendant out of the back of the patrol car. Often busy officers will ask the suspect for a sample immediately after they arrive. If we can prove with incontrovertible evidence the 15 minute waiting period was not observed then under the TX CCP Sec. 38.23 we can suppress the results of the breath test. This means that if you were over the limit – no matter how much – this evidence cannot be used against you.

Problems with PBT’s in Cold Weather – In cold weather, previous samples remain in the PBT machine and get added to subsequent samples. Therefore, at peak times for drunk driving arrests in winter the cumulative effect after several tests can result in falsely high breath tests for those who blow into the machine after several others have blown before them.

Radio Frequency Interference and Portable Breath Tests

Another big problem with the PBT machine is that it has no way to screen out interference caused by radio frequencies. These cannot be heard so the only thing police can do is to avoid sources of RFI – which is practically impossible: hand-held and car-mounted radio transmitters, cell phones, CB radios, light bars, computer terminals inside the patrol vehicle, and police radar. Obviously, there is no way the officer will be able to escape all radio frequency interference with the PBT when using it to decide if you are drunk enough to be brought into the station for further testing. (The Intoxilyzer 5000 EN does have radio frequency detectors per DPS requirements.)

Improper Calibration and Bias – some police agencies don’t perform routine or preventive calibration or verification checks for the PBT’s at all – ever – while they are deployed for use in the field. In some instances where they are calibrated or checked, these tests are poorly designed. And there are many variations in taking the sample based upon each subject’s physiological differences and the stage of ethanol metabolism their body is in – all of which the PBT machine is designed to interpret with a programmed bias toward a higher rather than a lower reading.

PBT Not Admissible in Court – There are NO approved PBT devices and NO approved reference sample devices on the DPS-approved Texas breath test instrument list. This is why PBT results are not admissible in court as proof of a defendant’s particular blood alcohol level.

Given all of the above you can see that the PBT is not scientifically reliable. But it is a false PBT reading which often plays a part in and often leads to a false arrest for DWI, which negatively impacts peoples’ lives in so many ongoing ways, personally, professionally and financially. A better understanding and appreciation of the PTB machine’s limitations must be spread among defense and prosecuting attorneys as well as in the public to prevent wrongful arrests and convictions.

Harris County DWI Attorney

If you or a loved one have been arrested and charged with a DWI in Houston, don’t hesitate to contact Carl Haggard of The Haggard Law Firm for a free confidential consultation about your case. Carl has over 30 years of experience defending the rights of people in Harris County and will fight for you.

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