When people are stopped on suspicion of DWI in Minnesota it is common for an officer to administer a breath test to determine the driver’s level of impairment. These Breathalyzer tests tell the officers how much alcohol is in the driver’s system at the time, allowing the officer to decide whether the person is legally impaired and deserves to be arrested.

Though you may have heard of Breathalyzer tests, the concept is still confusing to many people. How do the tests work? Why are they used in the first place? Are they accurate? To find out more, keep reading.

Why use a breath test?

Breath tests measure someone’s blood alcohol concentration (BAC) and are designed to give the officer an idea of how much alcohol is in a person’s system, a number reflected as a percentage. Given that the issue involves blood, why are people not given blood tests?

The reason that breath tests became so popular is that they are so easy to administer. It is not practical for officers to have to haul every driver they suspect of being impaired into a hospital to have blood drawn. The same problem exists with urine tests. Officers needed to find a minimally invasive way of determining impairment without wasting time and resources on elaborate testing procedures. As a result, breath tests were developed by police departments dating as far back as the 1940s and have become increasingly popular since.

How do the tests work?

Breathalyzer tests work by measuring the amount of alcohol present in a person’s lungs. The alcohol content of the lungs reflects the amount of alcohol that is in a person’s bloodstream, something that scientists proved after a lot of experimentation. In fact, they have been able to show that the ration of breath alcohol to blood alcohol is a fairly precise 2,100 to 1.

So does this mean that you swallowed a sip of alcohol and immediately took a breath test that you could be found to be drunk? Unlikely, given the way the tests work. Though your breath could smell like alcohol, the air in your lungs would not have had a chance to absorb the alcohol and that is what the test measures.

Are breath tests accurate?

Though scientists have worked hard to ensure that breath tests accurately portray a driver’s level of impairment, the reality is that nothing is perfect. One study out of the Wisconsin State Laboratory of Hygiene found that only 33 percent of Breathalyzer tests administered in a test corresponded to the blood test results. Another study out of the University of Washington estimated that Breathalyzer accuracy can vary by as much as 15 percent from actual BAC levels.

The reality is that a range of factors including your diet, operator error, calibration problems, even mouthwash can throw off the results of a breath test. These possibilities for trouble underscore how important it is to hire a skilled Minnesota DWI attorney who understands the process of challenging unjust results.

Source: “How Breathalyzers Work,” by Craig Freudenrich, published at HowStuffWorks.com.