Several different types of DUI breath tests detect levels of alcohol present on a person's breath. At the scene of a DUI incident, Preliminary Breath Tests (PBT) most commonly used. PBTs are portable handheld devices. They typically have an LCD readout, and lack the ability to print the result. The results of a PBT are generally not admissible in court. PBT results help the officer determine whether or not probable cause exists for your arrest. This means that the prosecutor and police can not use the results against a person accused of DUI in trial. Furthermore, a suspect usually has absolute ability to refuse to submit to test and the prosecutor is unable to legally hold it against them.
Even if you know you are under the legal limit, you shouldn't blow into a PBT. These machines are inaccurate, as that's why their not used against you in court. Once you blow into the device, it is the difference between arrested or not. On the other hand, the officer will probably arrest you if you refuse. Nevertheless, we think the better course of action is to politely refuse and let a blood test sort it out. PBTs are good party entertainment device, and their very useful in determining if there is alcohol in a persons system. However, PBTs not really good at predicting a specific alcohol level, and PBTs not designed to detect impairment.
DUI breath tests taken on larger, non-portable machines are Evidentiary Breath Tests (EBT). The results produced are admissible in court. A DUI suspect will blow a sample of breath through tube into chamber where it's analyzed and measured by machine. It is not uncommon for more than one sample taken. A suspect requested to blow into the machine 2-3 times. Multiple samples taken and compared to ensure the most reliable and accurate result. A print out reading will be provided at the conclusion of the test.
Several types of these machines exist, ones most commonly used are Intoxilizer and DataMaster (or DataMaster CDM, pictured to left). Check your local state laws to determine what machine used in your jurisdiction.
Different Types of Breath Analysis for DUI Breath Tests
There are two main technologies for DUI breath tests in common use today, fuel cell and infrared. Of the two, infrared is most commonly used and generally accepted in the scientific community for use in court.
In infrared breath testing in DUI cases, a light passed through the sample and then measured. Various machines approach this measurement in different ways. Infrared light absorption is invisible to the human eye. Infrared radiation absorbs alcohol chemicals present in a person's breath at certain wavelengths. That absorption rate can be measured and transformed into a BAC (Blood Alcohol Content) reading.
How infrared and fuel cell done
Infrared Spectroscopy testing requires a person to blow into a tube connected to the breath machine. The breath sample flows through the tube to a testing chamber that contains infrared light. Alcohol chemicals present in the chamber absorb infrared radiation in the light. The breath testing machine then measures the amount of infrared light passing through the chamber or reflects off the breath. The machine then prints out a reading that converts the absorption into a BAC (Blood Alcohol Content).
In fuel cell testing, a process called electrochemical oxidation converts alcohol to acetic acid. Two generated electrons for each alcohol molecule spark an electric current. Supposedly this used to measure the amount of alcohol present on a person's breath. This method is not as reliable for testing purposes and thus not often used.
In addition to attacking the method of measurement in your DUI case, an experienced DUI defense attorney will also spend time challenging the procedures used to take and measure your sample. Regardless which type of technology used in your case, several human factors may exist that would interfere with your result.
If you have been arrested for DUI and submitted to a chemical test of your breath for purposes of determining your BAC (Blood Alcohol Content), contact an attorney in your jurisdiction for more information on the admissibility of it's results and the impact it may have on your particular case.