The Law Offices of Edward Harrington Heyburn, PC

How does the breath test instrument work?

There is a relationship between the amount of alcohol present in the breath and the amount of alcohol present in the blood. That relationship is a constant and is not dependent on sex, weight or metabolism of the individual or how much the individual consumed. Henry’s Law, defines the relationship between liquid and a gas as a ratio.

All breath-testing instruments certified in New Jersey use the 2100:1 blood/ratio to calculate the blood alcohol concentration of an individual. This ratio is biased in favor of the accused.7 The instrument collects a breath sample, analyzes the sample for alcohol content, multiplies the result by 2100 and reports the result as the individuals BAC. A sample of deep lung air is required for analysis. Deep lung air is where the exchange takes place between the capillaries and the air sacs. The capillaries contain the blood that is mixed with alcohol.

Infrared breath testing instruments utilize a source of infrared light to analyze a breath sample and report an individual’s BAC. Each molecule of alcohol absorbs infrared light at particular wavelengths within the spectrum unique to alcohol. Beer’s Law states that a relationship exists between light passed through an absorbing material and the amount of light that is absorbed. This relationship can be measured or quantified. With respect to breath testing, the light is the infrared light given off by the source and the absorbing material is the ethanol molecules present in the deep lung air sample.