How Blood Alcohol Concentration Works

The national blood alcohol concentration (BAC) limit is .08 percent, .04 percent for commercial drivers and "zero tolerance" for drivers under the age of 21 in California. Exceeding the established BAC will result in drunk driving charges. BAC can make or break a DUI case.

Blood alcohol concentration is tested two main ways: through breath tests and blood tests. In some cases, law enforcement allows urine tests as an alternative BAC testing option. Breath, blood and urine tests all fall into the category of chemical tests.

It may be relatively easy to understand what BAC limits are against the law and what tests determine BAC, but it is a little more complex to understand how blood alcohol concentration works. In this blog, we will answer two major questions:

  1. How does BAC testing work?
  2. How does alcohol affect a person's blood stream?

Once a person is arrested under suspicion of DUI, law enforcement test their blood alcohol concentration by way of a breath or "Breathalyzer" test and/or a blood test. Breath tests measure BAC by measuring the chemical alcohol leaves behind on a person's breath after consumption.

As the blood goes through the lungs, some of the alcohol moves across the membranes of the lung's air sacs (alveoli) into the air, because alcohol will evaporate from a solution -- that is, it is volatile. The concentration of the alcohol in the alveolar air is related to the concentration of the alcohol in the blood. As the alcohol in the alveolar air is exhaled, it can be detected by the breath alcohol testing device.

Alcohol concentration in a person's breath sample correlates to the real concentration of alcohol in a person's blood. However, breath tests are not as accurate as blood tests. Blood tests are more direct, because blood absorbs alcohol. Law enforcement or a licensed medical person will take a blood sample and send it to the Orange County Crime Lab for assessment (if the arrest took place in Orange County).

The effects of alcohol are detectable almost immediately. If enough alcohol is consumed, it can affect an individual's central nervous system (CNS) and significantly impair their judgment. All states have adopted the .08 percent standard because this is the generally accepted level at which a person becomes impaired by alcohol consumption.

Alcohol affects each person differently. For example, a person's weight and gender play large roles in how many drinks a person can have before they are legally drunk. Other foods and drinks consumed can also affect the severity of alcohol's impact on your blood stream. For example, having two drinks with food will increase the amount of time it takes for the alcohol to reach the highest level. If you are interested in estimating your blood alcohol concentration, visit the BAC calculator.

If you've been arrested, do not hesitate to contact an Orange County DUI attorney at The Law Offices of Virginia L. Landry.

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