How Does a Breath Testing Machine Work?


When a Texas driver is pulled over on suspicion of driving while intoxicated (DWI), he or she may be asked to give a breath sample. Breath-testing machines, including the Breathalyzer and DataMaster, use the breath sample to check for the presence of alcohol in the driver’s bloodstream and to estimate the amount of alcohol present. Because breath testing machines can only estimate alcohol concentrations, an experienced Austin criminal defense attorney from Peek and Toland, LLP can employ a defensive strategy that emphasizes the inaccuracy of breath testing results to absolve you of drunk driving charges.

It is scientifically proven that Breathalyzers are often inaccurate and commonly unreliable, and therefore the attorneys at Peek and Toland, LLP do not ever recommend providing a breath sample unless required by court order. Below are just a few of the many reasons for the inaccuracies.

First, breathalyzers operate under the assumption that the sample taken contains alcohol from the lungs. To calculate the amount of alcohol in the blood, the amount in the breath sample is multiplied by the breathalyzer’s internal computer. If the sample is not from the lungs but from the mouth, throat, or stomach, the amount of alcohol should not be multiplied, or the result will be falsely high. The failure of breathalyzers to distinguish between alcohol coming from the lungs and alcohol already in the mouth or throat is a grave and common problem. A common source of mouth alcohol is acid reflux disease, which an estimated 1/3 of us occasionally suffer from.

Secondly, the computers inside Breathalyzers actually multiply the amount of alcohol in a DWI suspect’s breath sample 2100 times to get the blood alcohol concentration “BAC”. This is because it is programmed to assume that the suspect has 2100 units of alcohol in his or her blood for every unit of alcohol in his breath. This is called the “partition ratio”. But this ratio is only an average: actual ratios vary from as low as 900:1 to as high as 3500:1. If an individual’s ratio is different, the BAC result will be different.

A third common reason for inaccurate results is any change in a person’s body temperature. If because of illness, for example, the body temperature is elevated by only one degree Centigrade, the 1:2100 partition ratio used by breathalyzers will be altered so as to produce a seven percent higher test result.

Breath testing machines will also not work properly if the sample is corrupted or if the machine is not calibrated correctly. A false reading may be artificially high, prompting criminal charges where they are not appropriate.

To learn more about your rights in the wake of a DWI charge, call us today at  (512) 399-2311 and receive a free consultation.

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