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How Blood Alcohol Concentration is Used in DUI Investigations

The United States’ blood alcohol concentration, or BAC, level is 0.08 percent. For commercial drivers, the BAC limit is 0.04 percent. California has a different BAC limit for drivers under the age of 21 years old. It’s 0.00 percent. In other words, the state has a zero tolerance for underage drivers who choose to operate a vehicle while under the influence.

Exceeding the legal limit will result in a driving while under the influence of alcohol, or DUI, charge. BAC results can make or break a DUI case for a driver trying to fight the charge.

The blood alcohol concentration in a driver’s bloodstream is found in two ways: blood and breath tests. Under some circumstances, the law permits the police to use a urine sample as an alternative to the blood and breath tests. The urine, breath and blood tests are all referred to as chemical tests.


Understanding BAC limits in California and around the country is easy. It’s also easy to understand how BAC is determined in a DUI investigation. What’s more complex is how the blood alcohol concentration actually works. To simplify the complexity of how BAC actually works, we’ll answer the following questions:

  • How BAC testing actually works?
  • How alcohol affects an individual’s bloodstream?

How BAC Testing Actually Works? 

After an individual consumes alcohol, blood travels through the lungs. Some of the alcohol consumed moves across the membranes of the lung’s alveoli, or air sacs. The alcohol moves from the membranes to the air causing the alcohol to evaporate. The amount of alcohol in the alveolar air is related to the concentration of alcohol in the blood.

Once a driver is arrested for being under the influence for alcohol while operating a vehicle, police test his blood alcohol concentration. This is usually done via a breath test, or Breathalyzer test, or a blood test. In simple terms, after consuming alcohol, a person has an alcohol chemical left on his breath. The amount of alcohol chemical is tested using the breath test.

How Alcohol Affects an Individual’s Bloodstream?

Alcohol concentration in a driver’s breath sample relates to the amount of alcohol in a person’s blood. However, breath tests aren’t always the most accurate was test a driver’s blood alcohol level. Blood tests can be better than breath tests because the blood absorbs alcohol.

The effects of alcohol are found immediately. If there’s enough alcohol consumed, it affects the driver’s central nerves system. It can significantly impair a driver’s judgment. The amount of alcohol can play a major part in how the alcohol affects the driver. For example, alcohol consumption can affect each person depending on:

  • Weight
  • Gender
  • Food consumption 

For example, having two alcoholic beverages with food will take the alcohol longer to reach the highest BAC.

The Law Offices of Jonathan Franklin is ready to Help You with Your DUI Case

If you are arrested and your blood alcohol concentration, or BAC, is higher than the legal limit, don’t despair. It’s time to act quickly. Contact an experienced DUI attorney immediately. Time and evidence preservation is essential to fighting and winning your case.

You need a DUI attorney ready to fight for you. Here at the Law Offices of Jonathan Franklin, we’ll work hard to make sure you receive the representation you need to successfully fight your charge. No arrest is minor so we take on any type of DUI case from a misdemeanor to a felony.

Schedule a free consultation with us to immediately start resolving your DUI charge. In many DUI cases, high BAC results do not automatically mean a criminal conviction.  Call us today and take the first step towards resolving your matter and moving on with your life.

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Contact Information

Jonathan Franklin DUI Attorney
6777 Hollywood Blvd Ste 508
Los Angeles, CA 90028