The New Jersey legislature has defined intoxication as having a blood alcohol content of 0.08% or higher. Anyone whose blood alcohol content (BAC) exceeds this percentage is deemed to be legally intoxicated and cannot operate a motor vehicle. Law enforcement agencies in New Jersey have been looking for a dependable method of measuring BAC.

Several methods are used. If the suspect’s blood can be drawn, the amount of alcohol in the blood can be easily measured. However, drawing blood from a suspect in the midst of a traffic stop is not always practical or reliable, and the suspect cannot always be transported to a police station or hospital where blood can be drawn and analyzed. Using the suspect’s urine is similarly impractical.

In their search for a reliable method of measuring a suspect’s BAC, police turned to analyzing the suspect’s breath. If a person consumes alcohol, the alcohol is absorbed by the mouth, throat, stomach and intestines. Alcohol is not digested or chemically altered in the blood stream. Instead, as the blood passes through the drinker’s lungs, some of the alcohol passes through the lung’s air sacs (alveoli) because alcohol is volatile and will evaporate from a solution, i.e. the blood. As a person breathes, the air in the lungs passes across the alveoli during both inhaling and exhaling. Extensive testing has shown that the percentage of alcohol in the blood stream maintains a constant ratio to air in the lungs. Thus, by measuring the percentage of air in the lungs and multiplying the concentration by the known ratio, the amount of air in the blood stream can be measured.

Law enforcement agencies employ several different devices for making these measurements and calculations. The most common is the breathalyzer, which relies on a color change in a chemical solution to detect the presence of alcohol.

The breathalyzer contains two vials that are connected to a system of photocells to measure the degree of color change. The suspect breathes into a mouthpiece, and the breath is bubbled through one of the vials, in which sulfuric acid removes the alcohol from the breath. During the reaction, the reddish-orange dichromate in the alcohol changes color to dark green if alcohol is present in the blood. The degree of color change is then used to calculate the percentage of alcohol in the blood stream. The colored dichromate is compared to the other vial in which no reaction has occurred. This vial generates an electric current that moves the needle in the breathalyzer meter. The more alcohol is found in the blood stream the greater is the distance that the needle will move. The operated of the breathalyzer turns a knob to return the needle to zero. The number indicated by the knob provides the BAC.

A second type of device that measures BAC by analyzing the suspect’s breath is the intoxilyzer, which uses infrared spectroscopy to measure alcohol in the breath. The intoxilyzer passes infrared light through the breath stream. The amount of infrared light that passes through the breath is absorbed at different wavelengths depending upon the chemicals in the breath. The wavelengths that are absorbed can identify the presence of alcohol in the breath. The amount of IR absorption will determine the much ethanol is present.

The newest type of breathalyzer uses fuel-cell technology. The fuel cell has two platinum electrodes with a porous acid-electrolyte material between them. As the suspect breathes over the two electrodes, the platinum electrode oxidizes any alcohol in the air and creates a flow of electrons (an electric current). As the amount of alcohol becomes oxidized, an increase in the strength of the current indicates a higher amount of alcohol.

Despite the impressive science behind these various kinds of breathalyzer, they are not 100% reliable. An experienced defense attorney can often find failings in a particular device that will prevent the BAC reading from being offered into evidence.