How does a breathalyzer work?

What is a breathalyzer?

The term “breathalyzer” is actually the brand name of the breath analysis products manufactured by Smith and Wesson at the end of 1950, an improvement of more cumbersome “drunk meter” developed in 1938. The term, however, has become a generic term for any make or model of instrument designed to determine the amount of alcohol in the blood of a subject by analyzing the breath. Literally dozens of models of breathalyzers exist. Because of its frequent use as evidence in criminal courts, its design and operation it is subject to highly prescribed regulations.

How does it work?

Alcohol is not digested in the body; it’s simply absorbed into the tissues of the mouth, throat, stomach and intestines and finally excreted. In part leaves the body through breathing; because the total percentage of alcohol in the blood that exists in this way is predictable, the alcohol content of the breath can be used to calculate the total blood alcohol content, or BAC. The handheld breathalyzer technology uses electrochemical fuel cell to identify the elements present in the sample, of course, specifically looking for alcohol. Some devices use an infrared spectrophotometer to analyze the sample, identifying alcohol and calculate the percentage content. The BAC is then calculated on the basis of a partition ratio, the ratio of breath alcohol to blood alcohol, anywhere between 1,700 and 2,400. The result is a breathalyzer reading of alcohol in the blood is expressed as a percentage.

Factors affecting the accuracy of the breathalyzer

While the principles behind breathalyzers are solid, they can only estimate roughly the BAC as it is not measured directly. An artificially high or low reading may be due to several factors, all of which are often exploited by defense lawyers. To begin with, body temperature and blood composition can alter the partition ratio (individuals with reduced blood content display have an artificially high BAC reading). Vomiting or blood in the mouth or acid reflux can also distort readings. Most alcoholmeters cannot differentiate between ethyl alcohol and chemically similar compounds as ketones, acetone and gasoline, so that the presence of these substances in the test environment or in the metabolic system of the subject will also be a falsely high reading. A recent drink can also cause abnormal reading because the portion of blood alcohol consumption is delayed for several minutes. Finally, electrical interference from cell phones and police radios or incorrect calibration may produce unreliable results.