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

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. This is the test that you should not refuse (the implied consent test). The one given at the police station.

The EC stands for electrochemical and this is how this machine tests the amount of alcohol in the subject’s breath. There is a small wafer about the size of a quarter in a chamber inside the machine. 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 breath is drawn at the end of a sustained breath to insure that deep lung air is tested. A portion of the 1 ml sample alights on the platinum.

When the alcohol vapor in the breath sample lands on the platinum/electrolyte, the O-H bond of the alcohol (C2H5OH) is oxidized. The positive H ion at the end of the molecule is removed and floats to the bottom of the disk. This creates an abundance of electrons (-) at the top of the disk and an absence of electrons on the bottom because of the migration of the H(+) ions 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 greater the amount of alcohol present in the test chamber, the more electrons produced.

The IR in EC/IR stands for infrared. Infrared is used to control for mouth alcohol in the EC machines because the 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 213-893-8640 to discuss fighting and winning your DUI.


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