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The Complete Handbook of Breathalyzers
A practical reference for professionals, businesses, and serious users evaluating, deploying, and maintaining breath alcohol testing equipment
by Alumigogo Books
Chapter 1: Understanding Breathalyzers
A breathalyzer is an instrument that estimates a person's blood alcohol concentration (BAC) by analyzing the ethanol vapor in their breath. It sits at the intersection of chemistry, physiology, and law—measuring a gas to make inferences about a liquid state in the bloodstream, with consequences ranging from criminal liability to employment decisions to medical monitoring. Understanding how it works, why the method is imperfect, and what it can and cannot reliably tell you is the foundation for using one correctly.
What Breathalyzers Measure
When a person drinks alcohol, ethanol enters the bloodstream through the digestive system. The lungs act as a gas exchanger: as blood flows through the pulmonary capillaries, dissolved ethanol volatilizes and moves into the alveolar air—the air in the small sacs of the lungs where gas exchange happens. A person exhales this ethanol-laden breath, and a breathalyzer samples it to estimate BAC.
The key word is estimate. A breathalyzer does not directly measure blood alcohol; it measures the concentration of ethanol gas in exhaled breath and uses a mathematical relationship—called the partition ratio or breath-to-blood ratio—to convert that breath measurement into an inferred BAC. In most jurisdictions, the legal assumption is a partition ratio of 2100:1, meaning there is one unit of ethanol in the blood for every 2100 units in the breath. In reality, this ratio varies between individuals and even within the same person depending on physiology, body composition, breathing pattern, and how recently they drank. This inherent variability is