Frequently Asked Questions: Blood Alcohol Concentration (BAC)

Insight from a Boston DUI Lawyer

If you have been charged with operating a vehicle under the influence (OUI) in Boston, you should understand the facts of your case, including the measurement by which you were charged. Blood alcohol concentration (BAC) is the primary evaluation used to assess the intoxication of a driver. For further assistance with your OUI, contact our firm at once. We are available to fight your case based on any inaccuracies or improper testing procedures.

When discussing OUI (operating under the influence) or DUI (driving under the influence) arrests, tests and charges, the subject of one’s blood alcohol concentration, or BAC, is bound to arise. This is one of the key parts of any drunk driving case, as it refers to the method of measurement used to describe the amount of alcohol in one’s system. If a person drives with a blood alcohol level exceeding a certain amount, he or she may face criminal charges for DUI – regardless of the impact of the alcohol on that person’s driving ability.

What does blood alcohol concentration represent?

Your blood alcohol concentration level is a chemical measurement of the presence of ethyl alcohol in the bloodstream.

In Massachusetts and across the United States, the legal limit for blood alcohol content is 0.08%. If your BAC is at 0.08 or higher, operating a motor vehicle is a serious legal offense. The more you consume, the higher your BAC will be. Many factors, however, can influence a person’s BAC.

Factors that affect a person’s BAC are:

  • Amount of alcohol you consume
  • Period of time in which the alcohol was consumed
  • Body size
  • Amount of food in your stomach
  • Type of mixers used
  • Gender
  • Duration of time you have been drinking

Measurements of Alcohol in the Body

If one drink is equivalent to 1.25 ounces of 80 proof liquor, 12 ounces of beer or 5 ounces of wine, a 200-pound man may experience a .08% BAC after 4 drinks. A 120-pound woman may experience a .08% BAC after just 2 drinks.

Alcohol is measured as weight per unit of volume, and this measurement is converted into a percentage. If a person has a BAC of .05%, for example, this would indicate that one-half of a percent of that person’s blood is alcohol. With a BAC of .08%, a person is considered legally “intoxicated” or “under the influence” of alcohol, depending on the specific wording under the applicable state law. Lower BACs apply for drivers under the age of 21 (.02%) and commercial drivers (.04%).

To determine a driver’s BAC after a DUI or OUI arrest, law enforcement will request that the driver take a chemical test, either a blood test or a breath test. A driver may face license suspension for refusing such a test after a lawful OUI arrest, to the tune of 180 days for a first OUI offense for a driver over the age of 21. Increased penalties apply if the driver has prior OUIs or is under the age of 21. Similarly, a driver may face license suspension and criminal charges if he or she takes a breath or blood test and fails with a result of .08% or greater. Administrative license suspension penalties are less for a failed breath test than a refused breath test, but if the driver is convicted in criminal court, he or she may face imprisonment, fines and other criminal penalties.

Your Blood Alcohol Level and Massachusetts OUI Charges

If you were arrested for suspected OUI and are now facing criminal charges because you took a breath test or blood test that showed a result of .08% or greater, you have much to gain by involving a competent attorney. As Boston DUI lawyers, we at Keegan Law understand exactly what goes into determining a driver’s blood alcohol level and how these tests can be challenged. Our familiarity with criminal court proceedings and Registry of Motor Vehicle (RMV) hearings can make all the difference in protecting a client from imprisonment, fines, license suspension and other serious penalties. Contact our firm today to get started.