How does a Breathalyzer test determine one's blood alcohol level?

A law enforcement officer may utilize different tests and pieces of equipment when trying to determine if a driver is impaired. One piece of equipment often used is a Breathalyzer. Many people in West Virginia may have heard of this device but are probably unaware of how it works. So, how does a Breathalyzer test determine one's blood alcohol level?

The Breathalyzer machine is just one of many types of breath testing devices. When a person has been pulled over for suspected impairment, the officer will typically request that he or she supply a breath sample by blowing into the Breathalyzer machine. This is, of course, something that a driver can refuse, but there are consequences -- such as an automatic license suspension -- for not complying.

When a suspect blows into the device, the sample enters one of two vials in the machine that is full of a specific variety of chemicals. If alcohol is detected, a chemical reaction occurs, causing a photocell system in the second vial to change colors. The more alcohol in one system, the more significant the color change. This then produces an electric current which gives a blood-alcohol content readout. In South Carolina, anything over a .08 is considered intoxicated.

A lot is going on during a Breathalyzer test. While these devices are believed to be accurate, who is to say that a problem with the chemicals inside did not occur or that a cleaning or calibration issue is not to blame for a high readout? Any number of things could result in a false reading. Those in West Virginia who have been accused of drunk driving can question the results of breath tests. One's legal counsel will be able to assist with this and all other aspects of fighting a DUI charge in criminal court.

Source:, "How Breathalyzers Work", Craig Freudenrich, PH.D, Accessed on Feb. 4, 2016

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