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Traffic Law

Missouri DWI/DUI/BAC Breath Alcohol Testing (Breathalyzer Test)

The two most commonly used breath alcohol test machines (Breathalyzers) in Missouri are the Intoxilyzer 5000 (CMI, Inc.) and the BAC DataMaster (National Patent Analytical Systems, Inc.)

*How “Breathalyzers” measure blood alcohol content.*

The Intoxliyzer 5000 and the BAC DataMaster both use Infrared Spectrometry / Spectroscopy (IR) to measure breath alcohol concentration, from which blood alcohol content (BAC) is calculated.

The basic premise underlying IR is that every gas molecule will absorb energy in the form of electromagnetic radiation at a unique and specific wavelength. The pattern of absorption thereby creates a “fingerprint” (most commonly expressed in percent transmittance) by which that molecule may be identified. Using IR, the machines are designed to identify the presence and concentration of ethanol in a breath sample.

There are several steps involved in these machines using IR to determine blood alcohol concentration. First, a quartz lamp generates infrared (IR) light. The IR light travels through a chamber containing the breath sample. After passing through the chamber, the light travels through narrowband infrared filters and is focused on a photo detector. The photo detector converts the IR light pulses into electrical pulses which a fed into a microprocessor. The microprocessor uses a pre-programmed formula to “interpret” the electrical pulses and derive a number representing the “Blood Alcohol Concentration” which then is displayed.

Infrared Spectometry / Spectroscopy (IR) Breath Alcohol Test Machine (Breathalyzer)