How a DUI Breath Test works. We know the Science for You.

By otmseo on August 24, 2020

Here’s How the Breath Test Works in Los Angeles County.

In Los Angeles, the CHP and LAPD use the Intoximeter EC/IR machine to breath test those they arrest for DUI. You should not refuse (the implied consent test). This is the test given at the police station.

The EC stands for electrochemical. This is how this machine tests the amount of alcohol in the subject’s breath. Inside, the machine has a small wafer about the size of a quarter in a chamber. The wafer is covered in platinum stretched thinly over an acidic electrolyte. A positive electrode is attached to the top of the disk and a negative electrode is attached to the bottom of the disk.

A small (1 milliliter, 0.001 liters, 0.1 cubic centimeters) sample of the subject’s breath is drawn into the chamber containing the platinum disk.* The machine uses breath from the end of a sustained breath to insure that deep lung air is tested. When, it get to the chamber, a portion of the 1 ml sample alights on the platinum.

What Happens With the Breath Sample.

The O-H bond of the alcohol (C2H5OH) is oxidized when the alcohol vapor in the breath sample lands on the platinum/electrolyte. Once oxidized, the positive Hydrogen ion at the end of the molecule is removed and floats to the bottom of the disk. This results in an abundance of electrons (-) at the top of the disk and an absence of electrons on the bottom. This is because the Hydrogen(+) ions migrate to the bottom.

The electrons then move from the positive electrode at the top of the disk to the negative electrode at the bottom of the disk. This creates a charge in the fuel cell which is led off by the negative electrode and measured. The oxidation process creates a net of two electrons per molecule of alcohol. The more electrons that are produced means a greater amount of alcohol present in the test chamber.

The IR in EC/IR stands for infrared. Infrared is used to control for mouth alcohol in the EC machines because they do not do so on their own. Traditional machines contain a slope indicator to control for mouth alcohol. Infrared technology shines an infrared beam across a chamber filled with mouth air. The alcohol in the mouth air absorbs the infrared at 3.45 microns and 9.5 microns.

* An average male adult’s lung volume is 4.8 liters or 4800 milliliters. The sample size is 1/4800 of its representative population. Blood Alcohol is measured statutorily as grams per 210 liters.

If you’ve submitted to a breath test and need to fight your case call me at 213-479-5322 to discuss fighting and winning your DUI.

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