Although criminal defendants have a presumption of innocence, the general public may rush to the wrong conclusion in some cases. People tend to put a lot of faith in forensic evidence, including chemical evidence.
The popularity of police procedural television shows has led to people assuming that chemical evidence presented during criminal court proceedings is accurate and reliable. Therefore, those who fail breath tests during traffic stops sometimes panic. They don’t understand how they failed the test and worry that their criminal conviction is all but inevitable.
Contrary to what people see on prime-time television and in other popular media depictions, chemical evidence is not automatically accurate or reliable. In fact, breath tests administered during traffic stops are notorious for returning false positives.
Why do breath tests fail?
There are numerous reasons why chemical breath test units return inaccurate results and false positives. In some cases, the issue stems from improper maintenance of the testing device. Police departments may not have downloaded necessary software updates, or they may have failed to calibrate the device recently. The delicate chemical processes involved in breath testing make careful maintenance of devices important to the reliability of test results.
Another reason that tests fail is that the system used to screen for alcohol on people’s breath is actually relatively broad. There are other compounds that can trigger false positives on chemical breath tests. People without alcohol on their breath or with trace amounts of alcohol could fail tests because of this issue.
People in the state of ketoacidosis, such as diabetics who cannot manage their blood sugar, could fail a breath test despite having nothing to drink. Certain medications could cause false positives. Specialized diets, including the keto or paleo diet, can also cause false positive results on breath tests. The possibility of inaccurate test results is so high that criminal courts in some jurisdictions don’t allow drunk driving cases to move forward if the only evidence the state has is a breath test.
Defendants who secure legal representation when facing drunk driving charges might be able to raise questions about the accuracy of their test results. Learning more about impaired driving laws and defense strategies could help defendants avoid a criminal conviction that could cost them thousands and saddle them with a lifetime criminal record.