If you've been pulled over by a police officer and were subjected to a breath test, and then arrested and charged for drunk driving, it might seem like there's not much you can do. If the police have all of that evidence, it might seem hopeless, even if you know that you'd barely been drinking. You might even become convinced that your blood alcohol content must've been over the legal limit of 0.08%.

In this situation, giving in and pleading guilty is the easy thing to do. Don't get too down on yourself! Just because it seems like law enforcement has a lot of evidence against you does not mean that you'll get convicted, especially when their best piece of evidence is a breath test.

Remember that the legal limit for your blood alcohol content, or BAC, is 0.08%. If your blood contains more alcohol than this, then you could be convicted for driving under the influence, also known as a DUI.

But this is the alcohol content in your blood, not your breath. The alcohol content of your breath is only an indirect way of determining what your BAC actually is. The science behind this is fairly simple: When you drink, alcohol goes into your blood. Your blood flow passes through your lungs, where some of the alcohol in your blood turns from a liquid into a gas. When you exhale, air – and the alcohol in it – comes out from your lungs. In this way, the alcohol content of your breath mirrors the alcohol content of your blood.

Law enforcement personnel claim that the amount of alcohol on your breath exactly mirrors your BAC, and this makes breathalyzers and other breath tests perfect ways of showing what your BAC is. However, this is not entirely true. Not only are there other sources of alcohol that can spike the amount of alcohol on your breath, but the way breathalyzers are administered can make for misleading readings. Both of these factors can lead to an unjust arrest, and create massive legal problems that you didn't deserve.

Breath tests can make inaccurately high readings if a relatively large amount of air recently moved up from your lungs and into your mouth. This happens whenever you hiccup or vomit, two things that often happen after having a couple of drinks. Even if this hasn't happened recently, your mouth is often full of “residual alcohol” – latent alcohol that comes from a variety of other sources, like decomposing food between your teeth.

These are just two examples of sources, other than drinking alcohol, that can make the alcohol content of your breath higher than your BAC, and make a breath test give an erroneously high reading that could get you into trouble with the law. To make matters even worse, most breath testing machines are designed to test breath at 93 degrees Fahrenheit, however, exhaled air can be as hot as 96 degrees. Because hot air holds more moisture than cold air, and because alcohol is a type of moisture, this difference in temperature can affect a breath test reading by as much as 20%.

These scientific details can make breath test results begin to sound a little dodgy. However, things get even more problematic when you consider how law enforcement can manipulate the results to get people in trouble if they don't like them, or if they want to pad their arrest statistics.

Breath testing machines need to be calibrated so they provide accurate readings. Unfortunately, police departments don't let independent parties do this – they do it themselves. If police are pressured to make more and more arrests, or if they're rewarded by promotion if they do, then they have an incentive to miscalibrate their machines. Even if they do take the high road, miscalibrations can happen by accident, and even well-calibrated breath testing machines fall out of alignment over time.

Lastly, police can manipulate a breath test's reading by making you blow more air than is needed into it. Most machines have a limited sample size, but still let you blow more air into it once it has enough to make a reading. If you keep exhaling, the only thing that you're adding is more alcohol. If a police officer knows this, and they want to arrest you for DUI, they can tell you to exhale until your lungs are empty, in order to elevate the BAC reading.

When it comes to DUI charges, breath test evidence is not the end of the story. Just because you failed a breath test does not mean that you were at or over the legal BAC limit to drive, and I know how to prove it. Call my law office at (404) 816-4440.