Understanding Blood Alcohol Levels and DUIs
How BAC is measured and the consequences of exceeding the legal limit
By Andra DelMonico, J.D. | Reviewed by Canaan Suitt, J.D. | Last updated on March 11, 2024 Featuring practical insights from contributing attorneys Nathan J. Dineen and Robert ReiffUse these links to jump to different sections:
- What Is a Legal BAC Level?
- BAC Levels Across the US
- How Is BAC Level Measured?
- Factors Affecting BAC Level
- Why Is BAC Important?
- Consequences of Exceeding Legal BAC Limit
- Consult a DUI Defense Lawyer
When you enjoy a glass of wine with dinner or a beer with coworkers at happy hour, you aren’t thinking about the amount of alcohol in the glass. You are enjoying your time and not worrying about what that alcohol will do to your body or mental state. Alcohol is ethyl alcohol or ethanol that gets created in liquids when certain ingredients go through a fermenting process.
When you drink alcohol, it increases your blood alcohol concentration (BAC). As your BAC increases, your ability to safely operate a vehicle decreases, putting you at greater risk of getting arrested for driving under the influence or causing an accident.
What Is a Legal BAC Level?
When you drink alcoholic beverages, your body metabolizes them by processing the alcohol by absorbing the alcohol through your stomach and small intestines. From here, the alcohol enters your bloodstream. Your liver then identifies the alcohol as a toxin and begins filtering it out. When you drink alcoholic beverages faster than your liver can filter it out, the alcohol accumulates in your bloodstream. A chemical test measures the amount of alcohol in your bloodstream. This is your blood alcohol level (BAC). It can range from 0 percent or no alcohol to over .4 percent, which is a potentially fatal amount.
Generally, your liver can process one alcoholic beverage per hour. This would be the equivalent of five ounces of wine, 12 ounces of beer, or 1.5 ounces of liquor. However, this can vary because different beers, wines, and liquors have varying alcohol by volume percentages.
BAC Levels Across the US
The legal limit across most states is a BAC of .08 (in Utah, it’s .05). If your BAC measures .08 or higher, there is a presumption that you are too intoxicated to operate a motor vehicle safely. You do not have to have a BAC over this limit to get a DUI. You can still be arrested and charged with DUI if you are unable to pass field sobriety tests, appear intoxicated, or your normal faculties are impaired.
Commercial Driver’s License
Individuals with a commercial driver’s license (CDL) must adhere to a lower BAC standard of .04. Commercial vehicles are much larger, requiring more attention and skill to operate safely. An interest in public and road safety warrants the BAC limit, which is half the limit for regular driver’s licenses.
“The blood alcohol limit of .04 only applies when driving a commercial vehicle,” says Nathan Dineen, a DUI attorney in Germantown, Wisconsin, who represents CDL holders facing DUI charges. “Even though you have a CDL, if you are driving on your Class D license and in your personal vehicle, the legal driving limit would be .08.”
Underage Drivers
States have even stricter BAC limits for underage drivers. Many states have a zero-tolerance policy of 00 BAC for drivers under the age of 21, including:
- Alaska
- Arizona
- Illinois
- Maine
- Minnesota
- North Carolina
- Oregon
Other states have a BAC limit of .01 or .02 for underage drivers.
How Is BAC Level Measured?
Typically, blood alcohol level is reported as a percentage. However, you may also see it written as grams per milliliter (g/mL). When you take a breathalyzer test, the testing equipment measures the alcohol in the air you exhale from your lungs. A blood test measures the amount of alcohol in your bloodstream.
Breathalyzer Test
A breathalyzer test measures the amount of alcohol that gets diffused as vapor from the membranes in your lungs. Breathalyzer testing procedures require breathing into a machine designed to capture and measure your exhaled air. To administer the test, you will breathe deeply into a mouthpiece on a special machine for a specific time. After using a programmed formula to measure BAC, the machine will then output a number.
Blood Test
A blood test is another commonly used method for measuring BAC. Unlike a breathalyzer test, an officer cannot perform this test. It requires a medical professional trained in the ability to draw blood. The blood sample then gets sent to a lab for testing. The lab will return a report that lists your blood alcohol content. You do not have to do anything but sit still. The procedure of drawing blood takes about five minutes.
Factors Affecting BAC Level
Several factors can impact the accuracy of a chemical test meant to measure BAC. The timing of the test is crucial because your body does not stop processing the alcohol. A blood test is only accurate within six to 12 hours after consuming your last alcoholic beverage.
The amount of alcohol in your system will vary based on the number of drinks you consume, how fast you drink them, and their alcoholic strength. Other factors can impact BAC, such as what food and how much of it you ate before and while drinking. Finally, your gender, body weight/size, and age will impact how your body metabolizes alcohol.
Robert Reiff is a criminal defense attorney in Miami, Florida. He explains that sobriety tests require careful testing procedures for accurate results. “The problem with breath testing is that they’re supposed to look for deep lung samples, which would be accurate. They also need a fixed temperature. If you have any illness, anxiety, or stress, your internal heat goes higher. These factors can result in an inaccurate test result.”
Why Is BAC Important?
Your blood alcohol level is important because it is a data-centric measurement of your impaired ability to drive. Alcohol affects everyone differently, but there are some common trends. BAC helps to standardize the level of impairment.
If your BAC is .00, there is no alcohol in your blood, so you are sober. If your BAC is between .02 and .05, you likely feel relaxed, have a slightly altered mood, are less alert, and have the beginning signs of judgment loss. With a BAC of .08 to .10, you will experience slowed reaction times, reduced coordination, slurred speech, and significantly impaired thinking/judgment ability. When your BAC rises between .15 and .30, you will experience drowsiness, nausea, vomiting, loss of muscle control, and impaired balance.
Once your BAC rises above .30, you are now likely to experience alcohol poisoning. This is life-threatening, and you should receive emergency medical care. You will probably suffer loss of consciousness or fall into a coma.
These are general guidelines, though. Everyone’s body responds to and metabolizes alcohol differently. Your BAC level could be below the average, and you experience more severe or impactful effects. Other individuals may develop a tolerance to alcohol. They may not feel the same effects of alcohol as others who have drank the same amount. This does not mean their BAC is lower.
Consequences of Exceeding Legal BAC Limit
You will face several consequences if you exceed the legal BAC limit. After your arrest, you could receive a DUI conviction. This will lead to losing your driving privileges through license suspension or revocation. You may have to serve jail time, use an ignition interlock device (IID), community service, alcohol abuse treatment or courses, and fines.
Your penalties for drunk driving can vary based on the circumstances of your arrest. A first offense will have less severe consequences than a second, third, or fourth DUI arrest. Some with a BAC just barely over the legal limit with no property damage or victim physical injury will typically have less severe consequences than someone whose BAC is significantly above the legal limit or who caused extensive property damage and physical injuries.
Enhanced Penalty Limits
Many states have enhanced penalties for drivers with a BAC level significantly above the .08 limit. Several states have enhanced penalties for individuals with a BAC of .15 or higher. However, enhanced penalty BAC limits can vary greatly, from .10 to .20. The hope is that increased penalties will encourage people not to drive with an elevated level of intoxication.
Enhanced penalties can include increased fines, longer suspension periods, longer required driving time with an ignition interlock device (IID), or mandatory minimum incarceration periods.
Consult a DUI Defense Lawyer
People often assume that once you go through chemical testing and have a BAC measurement of .08, you are guilty of DUI with no defense. However, this isn’t always the case. A defense lawyer can analyze the circumstances around your DUI arrest to determine the best possible defense. An experienced attorney can identify potential issues with testing your blood alcohol content to call into question the accuracy of your test results.
Visit the Super Lawyers directory to begin your search for an experienced DUI defense attorney. For more information on these legal issues, see our overviews on DUI/DWI Testing Procedures and how DUI is proven.
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