Had an interesting note from a jury yesterday: Do you average the two blows on an intoxilyzer result? The defendant blew .083 and .079. I had argued loss of mental/physical faculties. Defense attorney had argued she blew .079. The judge answered �all the evidence is before you� etc. The jury came back with a guilty.

Still, what did she blow? .079, .083, or .081 (the average)?

I would say that is the technical supervisor's area to explain the reasons why it is very difficult to exactly duplicate each blow and get two same results, and why the Intox instrument checks for the 0.02 agreement.

We've had to have our tech sup go through this before when questioned on it by the defense.

. . . She blew both results.

What I always explain to the jury is that both blows count. The only reason there are two is not because we need two to get an accurate result, but because by getting two samples within a set range we can be confident that both are accurate. I also point out the to jury that the instrument doesn't just check the two samples, either. There are also several air blanks and a reference sample, and we KNOW what those results should be (.00 and .08, assuming you supervisore uses .08 for the reference). So when we get 5 samples we KNOW to be accurate, mixed with the two questioned samples, what possible reason could there be to doubt that BOTH of those samples are accurate measures of the amount of alcohol in each sample when the other 5 samples are all right on the mark!

My understanding of the indicated BAC levels from the breath specimens is that it shows the BAC at the time of the specimen. If they are good specimens, the difference in their respective levels is suggestive of the absorption phase or elimination phase of the Etoh in the D's system.

If the first specimen's BAC is higher than the second, the D is metabolizing the Etoh and in the elimination stages (getting more sober), and if it is vice-versa, the D is getting more intoxicated because they are in the absorption phase. This gets into into the reverse extrapolation issues brought up by D's attorney and is the seed of doubt as to what the D's actual BAC was at the time of "operating a motor vehicle".

The technical supervisor for East Texas has explained it to juries that it is just part of being human - just like if you throw a baseball as far as you can, wait a few seconds and throw another one - they will go a different distance. He then uses the lower of the two numbers for his analysis. Not sure of the science of that metaphor - but it is something that juries understand - and using the lower number even with the prosecutor takes the wind out of the defense's sails for that attack.

I e-mailed the Scientific Director of the State's breath testing program (Mack Cowan--he just took over after Richard Baxter retired) with the question. Here is his response:

The longer a person blows, the deeper the sample from the lungs, the higher and more accurate the breath sample. Two tests two minutes apart that have different results are indicative of the sample given, not whether the person�s alcohol concentration is going up or down.

You can�t tell if a person is going up or coming down based on two tests two minutes apart. Further, if the tests were an hour apart, and you could tell if the person was going up or coming down, you still couldn�t use that information to determine what the person�s alcohol concentration was at the time of the arrest without substantial information about the drinking episode that can only be provided by the person tested. And if you have that information, two tests two minutes apart are enough to make the calculation just as accurately. In case you didn�t know, we need a time of test law.

If the attorney�s logic was correct and the first test was 0.100 and two minutes later the second test is 0.105, the person would have been 0.000 only 40 minutes before the first test and the subject had been under arrest for an hour or more.

We report both results. The higher value is almost always the more accurate result, but most prosecutors prosecute based on the lower value to give the defendant the benefit of the doubt.

Janette Ansolabehere
DPS Office of General Counsel

Janette: To summarize, the person almost certainly had a BAC equal to the lower test result and more likely had the higher result (since it was based on a deeper, more accurate or meaningful sample of aveolar breath). That makes sense to me- more than the baseball analogy- unless it is visualized as the harder you blow, the farther (and better) you throw.