« Blood Alcohol Measurement - How Breathalyzers Work

Breathalyzers are a common, household name. People are aware of them and what they're used for, but most people don't understand how they work. This article will describe How Breathalyzers Work and how they're effective at getting drunk drivers off the road (with a little help from the authorities, of course).

An Overview of How Breathalyzers Work

Breathalyzers work by measuring the level of alcohol in the blood, otherwise known as the blood alcohol content (BAC). To most, it might seem strange that blood alcohol content can be detected without the breathalyzer device being in contact with the blood. That is because it has been scientifically proven that the concentration of alcohol in the breath is mathematically related to the concentration of alcohol in the blood (by a ratio of 2100 to 1 - the amount of alcohol in 1 mL of blood is equivalent to the amount of alcohol in 2100 mL of your brath, or alveolar air). How does the the alcohol get into your breath after you drink it?

Alcohol, when ingested is absorbed through various parts of your body, from your mouth and throat, through to your stomach and intestines. The absorbed alcohol isn't digested and it doesn't change chemically when it enters the bloodstream. As the heart pushes the blood through your body, it eventually reaches the lungs, where some of the alcohol is pushed through the alveoli (air sacs in the lungs) and evaporates there. When asked to perform a breathalyzer test, the air from your lungs is exhaled into the breathalyzer device that detects the level of alcohol in the exhaled breath.

So How Does a Breathalyzer Device Measure the Blood Alcohol Concentration

There are actually three devices to measure BAC, with "Breathalyzer" being the generic name. All contain a mouthpiece to blow the air into, and a chamber where the device performs it's work. A real "Breathalyzer" measures BAC by using a chemical reaction that produces a change in color. The Alcosensor uses a fuel cell, which detects a chemical reaction. The Intoxilyzer uses infrared spectroscopy to detect alcohol.

The Breathalyser uses a complex chemical reaction. To put it simply, when the breath enters the device, the alcohol is removed from the air and made into a liquid solution. The liquified alcohol solution then reacts with a chemical in a vial inside the device, which causes a color change in the chemical, and the degree to which the resulting color change occurs is related to the level of alcohol that was brought into the system. However, the device actually measures the BAC by an electrical current difference between the vial where the chemical reaction occurs, and another vial inside the device where no reaction has taken place. The electrical current difference is responsible for the needle movement on the device or the changes in the display where the authority reads the BAC.

The Alcosensor uses fuel cell techology. When vaporized alcohol enters the device, a platinum electrode oxidizes the alcohol in the air. The platinum electrode is attached to another electrode which doesn't get oxidized. When the first electrode oxidizes, a measurable current can be determined between the two electrodes. This current is related to the blood alcohol content.

The Intoxilyzer measures the concentration of alcohol through the use of infrared spectroscopy, a method of idententifying molecules based on infrared light absorption. Ethanol, the active ingredient in alcohol, has unique properties that can be measured by the infrared device. After a breath enters the Intoxilyzer, an infrared lamp generates a beam, which passes through the sample chamber with the breath inside. As the light passes through the chamber, ethanol changes the wavelength of the light in a predictive way. After the light exits the chamber, a filter wheel, which has filters for the wavelengths coming from ethanol, filters out those wavelengths. The light detected passing through the filter is detected by a photocell beyond the filter, where an electical pulse is created. The pulse is interpreted by a processor, where the BAC is determined, based on the absorption of IR rays.



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Random Facts about Alcohol

Alcohol is the third leading cause of preventable mortality in the US, behind tobacco and diet/activity patterns. It contributes to 100,000 deaths annually.

J McGinnis & W Foege, "Actual Causes of Death in the United States," Journal of the American Medical Association {JAMA}, Vol. 270, No. 18, 11/10/93, p. 2208

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