What Is Blood Alcohol Content (BAC)?
You may have heard the term “blood alcohol content” (BAC) in relation to driving under the influence (DUI) of alcohol; however, understanding the meaning of BAC can be helpful in knowing if you’re complying with the law. Additionally, the more you know about BAC, the greater chance you have of challenging invalid evidence being used against you in a DUI case.
What is BAC?
The simplest definition of BAC is that it is the amount of alcohol in your blood steam. BAC is based on the mass of alcohol, measured in in grams, per volume of blood, measured in milliliters. A BAC of .08 percent in the context of mass per volume means there are 8 grams of alcohol for every 100 mL of blood. It is illegal for drivers over the age of 21 to operate a motor vehicle with a BAC of .08 percent or higher. For minors and commercial drivers though, the limits are zero and .04 percent, respectively.
How is BAC determined?
Your BAC can be determined through a breath test, blood test, or urine test. Blood tests are the most accurate way to determine your BAC. The police may ask you to undergo a BAC blood test, which cannot be done without your consent. However, if you refuse, you may face administrative and criminal penalties. Once your blood sample is taken, it will be tested by an authorized lab.
Breath tests have been determined to be accurate enough that they can be admitted in court, though they are not as accurate as blood tests. During a breath test, the machine calculates how much alcohol is in your breath. There are traces of alcohol in your breath because a small amount of the alcohol in your bloodstream moves into your lung tissue as your blood circulates. By understanding the ratio between alcohol in the breath and alcohol in the blood, the amount of alcohol in your breath can be translated to a BAC. Breath tests are not perfect. In fact, they can be affected by a number of factors, including calibration of the equipment, environmental issues, and other health factors and medications.
Urine tests are the least accurate of all BAC tests and are considered as intrusive as blood tests, so you must consent to taking them. However, again, you can be punished for refusing. Like translating a breath test to a BAC, the amount of alcohol in your urine is translated to a BAC based on a ratio of urine alcohol to blood alcohol. However, while there is an average ratio, further research has proven that the difference between urine alcohol and blood alcohol can be very different for individuals. As a result, urine test results can be much higher or lower than your actual BAC since a variety of individual factors determine the amount of alcohol that has been concentrated – or diluted – within your urine. These tests are also more likely to be inaccurate since they cannot be conducted for some time after the initial arrest.
How Does BAC Correspond to Intoxication?
Research has shown that certain BACs typically correspond to certain behaviors and physical and psychological effects. For instance, a small amount of alcohol can make you feel relaxed. However, an amount greater than .08 percent can lead to loss of judgement, coordination, and your inhabitations. Your vision, depth perception, and reflexes also become impaired. Between .11 to .20 percent, you can experience mood swings and your reaction time and speech are impaired. This is where slurred speech becomes common. When you have a BAC above .20 percent, you can black out and your physical abilities like walking become difficult to execute and control. At a BAC of .30 percent or higher you can lose consciousness and your breathing and heart rate are negatively affected. A BAC of .40 percent or higher can lead to medical events and death.
While each person is a little different and not everyone reacts to alcohol the same way, there is enough evidence to support these assumptions in court. So while it is true that not everyone behaves the same way with a BAC of .08 percent, there is enough scientific evidence to hold that this much alcohol within your system makes you incapable of safely operating a vehicle.
How is BAC used in DUI Cases?
Your BAC can influence a DUI case twice. First, it is relevant to whether prosecutors can move forward with a DUI case against you. If a BAC test comes back with a content of .08 percent or higher, you will likely be charged. However, you can also be charged with a DUI without a BAC at or above .08 percent. Second, your BAC at the time of the incident will be relevant at trial. Prosecutors will use your BAC test results as proof that you were too intoxicated to safely drive. However, your attorney can argue against your test results and what they mean as part of your defense to these charges.
Contact a Pittsburgh DUI Attorney For Help
Because BAC test results can be inaccurate, the tests can often be challenged successfully by a seasoned Pittsburgh DUI attorney. If you have been charged with a DUI in Pennsylvania, do not assume you will be found guilty and will lose your license for years. For more information, call the experienced criminal defense attorneys at (412) 281-2146.