How to Conduct a Breath Alcohol Test

Breath alcohol tests are used to determine if a person has an alcohol blood level above the legal limit. Testing can be done either by a police officer who has pulled over a driver who was showing symptoms of intoxication, or it can be done at a laboratory or company that specializes in drug and alcohol testing. Alcohol has been shown to be related to about 38 percent of traffic deaths in the United States in 1999. Over 42,000 people died from drunken drivers that year (Freudenrich, 2010).

Police officers typically use portable breath-testing machines to test drivers who they have pulled over for probable cause. Even if a driver can pass a roadside test by touching their nose or walking a straight line, the alcohol level in their blood might still be above the legal limit. Police officers test the blood alcohol concentration (BAC) in the suspect's breath.

The Breathalyzer, one type of testing devices used by police today, was invented in the 1940's by Dr. Robert Borkenstein of the Indiana State Police. It is able to test the BAC by measuring the alcohol on the breath. This can be done since alcohol is not digested or changed in the bloodstream. When the blood goes through the lungs, some of it moves across the alveoli, or the lung's air sacs. It has been proven that the alcohol in the alveolar air is related to the amount of alcohol in the person's blood. This means that it would be possible to take a blood sample to discover the alcohol level in the blood, but this is not practical for police officers to do. The Breathalyzer measures the BAC by measuring how much alcohol is in the lungs.

Many states have a standard of 0.08 for legal intoxication. If the Breathalyzer or other device shows that the driver's level is at this number or over, the driver is immediately removed from the road and is under arrest.

To conduct a breath alcohol test with a Breathalyzer, the suspect breathes into the device. Two glass vials hold the breath sample. One vial has a mixture of sulfuric acid, potassium dichromate, silver nitrate and water. Through a chemical reaction, the breath changes color if alcohol is present. The reacted mixture of breath is then compared to a vial of mixture that has not had these chemical changes take place. When a knob on the Breathalyzer is turned, the level of alcohol is shown.

Another type of device used to measure BAC uses infrared (IR) spectroscopy. Absorbed wavelengths are measured to identify ethanol, and the amount of IR absorption shows how much ethanol is in the breath.

Those who administer any type of breath alcohol test must be trained in the methods to use with these devices.

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