The Role of a Breath Test in a San Antonio DWI

In our recent blog entries, we discussed DWI defense techniques against Field Sobriety tests . Today, we will focus our discussion of Jourdanton DWI criminal defense by examining the Intoxylizer 5000 and a defense against a breath test over the legal limit.

A San Antonio DWI lawyer will have the TX Breath Alcohol Testing Program Operator Manual at his disposal as he prepares to defend against a breath test result from the Intoxilyzer 5000. Many ever-changing factors influence the machine (and the results it spews out), and these conditions will lay the foundation for challenging the accuracy of the breath test.

The Intoxilyzer 5000 simply has too many flaws to be used to prove results beyond a reasonable doubt. Much like a computer or vehicle, the machine is prone to malfunctions and inaccurate, unreliable results due to maintenance, operator error, lack of proper calibration, and simple glitches. Jurors can very well sympathize with the reliability issues associated with the machine especially if they have encountered problems with a computer or car.

The Intoxilyzer is based on a formula of 0.080g/210L. Essentially, eight (8) one hundredths of a gram has to be detected in two hundred ten (210) liters of air. TX Penal Code Section 49.01 outlines the same blood alcohol content of .08 – a blood alcohol content (BAC) over .08 means the person is intoxicated at the time of testing.


In order to convert the blood alcohol content (BAC) to an equivalent breath alcohol content (BrAC), the TX Legislature determined that 210 liters of air converted into 100 milliliters of blood. So , here are the equivalent formulas:

BAC – 0.080g/100ml of blood
BrAC – 0.080g/210L of air
When trying to prove the BAC through the equivalent breath sample, the prosecution calls upon the breath test operator and the technical supervisor. The breath test operator will discuss proper administration of the test to the driver and the Test Record, which is a piece of paper reflecting the quantities of alcohol per 210L of air. The supervisor will discuss the reliability of the Intoxilyzer 5000.

In our next section, we will discuss in further detail how a San Marcos DWI lawyer can attack the reliability of the breath test.

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