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Understanding BAC breath tests

On Behalf of | Mar 17, 2020 | DUI |

Most drivers know if asked by law enforcement to submit during a suspected drunk driving stop, they must provide a breath sample for testing. However, many do not understand how these tests work or the factors that may affect them. The blood alcohol content levels provided by these tests often play a significant role in drivers’ arrests and prosecutions for suspected driving under the influence. 

As people drink alcohol-containing beverages, the alcohol absorbs into their stomachs and bloodstreams. Some of the alcohol then gets exhaled through the breath as it is metabolized. That is where breath alcohol tests come in. 

How do alcohol breath tests work? 

Breath alcohol tests work by measuring the amount of alcohol contained in a person’s breath. Based on that measurement, these devices approximate the among of alcohol contained in the person’s oxygenated blood. According to The New York Times, when drivers provide breath samples, the alcohol in their exhaled breath reacts with the fuel cells in breath alcohol test devices. This reaction generates an electric current, which determines the alcohol level contained in the breath sample. 

What factors affect breath test results? 

Despite law enforcement’s reliance on their results during drunk driving stops, numerous factors may affect the accuracy of alcohol breath tests. Sensitive scientific devices, alcohol breath tests require an initial setup and regular calibration to work properly. Improper calibration may lead to devices giving readings as much as 40% too high. Software programming mistakes and poor maintenance may also affect the reliability of alcohol breath test results. 

In addition to factors related to the breath alcohol tests themselves, factors pertaining to the drivers submitting to such tests may also affect the accuracy of their readings. According to, breath alcohol tests may provide inaccurate readings as a result of smoking, using breath fresheners or mouthwash, or taking a drink within 15 minutes of the testing.