How does Breathalyzer Work?

You have probably heard about the Breathalyzer, but may wonder exactly how a person’s breath can show how much that person has had to drink. Police officers use some of the latest technology to detect alcohol levels in suspected drunken drivers.

Breathalyzers are used to measure blood alcohol levels (BAC). If police suspect someone of drinking and driving, along with some tests will ask to give a breath sample for a Breathalyzer device to make sure the legal limit of BAC .08. The Breathalyzer uses that air to measure your blood alcohol level. The actual ratio of breath alcohol to blood alcohol is said to be 2,100:1 – meaning that 2,100 milliliters of air from your lungs has the same amount of alcohol as 1 ml of your blood.

Here we examine the scientific principles and technology behind these breath alcohol testing devices. In addition to this, below you can find information about different types of Breathalyzer. Intoxilyzer and Fuel Cell Detectors are two types that are widely used now a days. This article contain ,detailed and interesting information about these breathalyzer.
How does Breathalyzer Work?

Working principle and Types of Breathalyzer

Working principle and types of Breathalyzer are explained below:

How does Breathalyzer Work?

Alcohol that a person drinks shows up in the breath because it gets absorbed from the mouth, throat, stomach and intestines into the bloodstream. As the blood goes through the lungs, some of the alcohol moves across the membranes of the lung’s air sacs into the air because alcohol will evaporate from a solution.

The concentration of the alcohol in the alveolar air is related to the concentration of the alcohol in the blood. So an officer can test the breath on the spot and determine whether there is a reason to arrest the driver.Breathalyzer hold a system to sample the breath of the suspect, two glass vials containing the chemical reaction mixture and a system of photocells connected to a meter to measure the color change associated with the chemical reaction.

To measure alcohol, a suspect breathes into the device. The breath sample is bubbled in one vial through a mixture of sulfuric acid, potassium dichromate, silver nitrate and water. The silver nitrate is a catalyst, a substance that makes the reaction go faster without participating in it. The sulfuric acid also might provide the acidic condition needed for this reaction.The degree of the color change is directly linked to the level of alcohol in the exhaled air. In this reaction, the reddish-orange dichromate ion changes color to the green chromium ion when it reacts with the alcohol.

To determine the amount of alcohol in the exhaled air, the reacted mixture is compared to a vial of unreacted mixture in the photocell system, which generates an electric current that causes the needle in the meter to move from its resting place. The operator then rotates a knob to bring the needle back to the resting place and reads the level of alcohol from the knob; the more that the operator must turn the knob to return it to rest, the greater the level of alcohol.

Breathalyzers: Types of Breathalyzer

There are three major types of breath alcohol testing devices based upon different principles:

  • A Breathalyzer uses a chemical reaction involving alcohol that produces a color change.
  • An Intoxilyzer detects alcohol by infrared (IR) spectroscopy.
  • The Alcosensor III or IV detects a chemical reaction of alcohol in a fuel cell.

Regardless of the type, each device has a mouthpiece or tube through which the suspect can blow air and a sample chamber where the air goes. The rest of the device will vary with the type.


Intoxilyzer uses infrared spectroscopy, which recognizes molecules based on the way they absorb IR light. Molecules are continuously vibrating and these vibrations alter with bending and stretching of various bonds when they absorb IR light.

Each type of bond within a molecule absorbs IR at different wavelengths. So, to identify ethanol in a sample, you would have to look at the wavelengths of the bonds in ethanol and measure the absorption of IR light. The wavelength assists to categorize it as ethanol and the amount of IR absorption tells you how much ethanol is there.

In the Intoxilyzer, a lamp generates a broadband IR beam. The IR beam passes through the sample chamber and is focused by a lens onto a spinning filter wheel. The filter wheel contains narrow band filters specific for the wavelengths of the bonds in ethanol.

The light passing through each filter is detected by the photocell, where it is converted to an electrical pulse. The electrical pulse is relayed to the microprocessor, which interprets the pulses and calculates the BAC, based on the absorption of infrared light.

Fuel Cell Detectors

Contemporary fuel cell technology has been applied to breath alcohol detectors. The fuel cell has two platinum electrodes with a porous acid electrolyte material sandwiched between them. As the exhaled air flows pass one side of the fuel cell, the platinum oxidizes any alcohol in the air to produce acetic acid, protons and electrons.

The electrons flow through a wire from the platinum electrode. The wire is connected to an electrical current meter and to the platinum electrode on the other side. The protons move through the lower portion of the fuel cell and combine with oxygen and the electrons on the other side to form water. More the alcohol oxidized, the greater the electrical current.

A microprocessor measures the electrical current and calculates the BAC. Operators of any breath alcohol testing device must be trained in the use devices, especially if the results are to be used as evidence.

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