Analyzing Blood or Breath Test Evidence
It is important to keep in mind that there are national protocols with respect to the scientific evidence in blood and breath cases, as well as police protocols, which are generally of a lesser standard than the national protocols. Therefore, it is essential to find out as much as you can about the blood and breath testing procedures in DWI cases.
For example, in a case we tried in San Antonio about two years ago we obtained the records of the technical supervisor who is supposed to keep the breath testing machines calibrated, in good repair, and functioning properly. A breath testing machine should be able to test for acetone, because if there are traces of acetone in your breath it can skew your BAC reading. Diabetics and people on high protein with low carbohydrate diets can have acetone present in their blood (and breath). In fact, acetone is such a volatile substance that minute levels will make it look as if you have much higher levels or alcohol in your system. Your actual BAC reading might be .04, but you may blow a .13 result if there is acetone on your breath.
A good breath testing machine is supposed to have filters that will keep other chemicals from being read and interfering with the result, but in the case I have mentioned, when the operator was running the acetone test and it was not giving him the correct response, he would simply just hit the delete button. I sent the testing records I had obtained to an expert in Dallas, and he noticed that the numbers were not lining up properly. He used to work for law enforcement; and at that time, he was told that even if there were errors in the breath test program he was not supposed to fix them. At that time he quit DPS and started his own company and does an honest job for the defense community. He would work for the state as well if they would pay his fee. The only problem for them is that he would tell the truth no matter which side it hurt or helped. Too often the government seemed to only be concerned with getting a conviction.
In some cases, we might tell the expert, “Our client looks good on the police video, but the breath test shows he had a .16 BAC level.” Our expert will then analyze the underlying data with respect to the breath test machine; and quite often he will discover that the police are covering up repairs, or their machines were taken out of service because of technical problems, but the police did not notify the lawyers of the clients who were tested on the machines on the proceeding days. Also, a breath test machine has a device called a mouth alcohol or slope detector, which is supposed to measure a drastic decrease in BAC while you are blowing. Let us say that I start blowing into the machine and at first it registers .18 and then it drops down to .12. There is no way that my body should be able to get rid of the effects of three beers in four seconds. In that case, the machine should detect a problem and restart the testing process. One reason why such a problem might occur is a sudden mouth alcohol incident, i.e., if you burp or suffer from GERD, alcohol vapor might get into your mouth from your stomach, not through your lungs, and that will skew the breath test results.
In Texas, a supervisor will generally test the breath testing machine by putting a drop or two of vodka on their tongue and then blowing into the machine. The machine will immediately start reading high, but it should go down to zero within a second or two, which indicates that the mouth alcohol detector is reading properly. However, in some cases your client might initially blow a .06 result, but his reading will suddenly go up to .09 simply because he recently ate a sandwich, and bread or particles of meat are stuck between his teeth. If he had a drink, the alcohol can get absorbed into the bread or meat; and that will affect the breath test result, just as if he had burped. Also, the longer you blow into the machine, the higher the BAC reading will be.
As an attorney in this practice area, it is important to make the jury aware of these issues. For instance, if your client burped during the testing process, the officer is supposed to provide him with a fifteen-minute observation period, but that does not always happen. Also, further testing might reveal additional problems, but in Texas the government does not do further testing.