How is BAC (Blood Alcohol Concentration) Calculated in Maryland?

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We take all sorts of important tests which could determine what can happen next in our lives. If you are pulled over for a DUI, that test is based on your BAC results, your “Blood Alcohol Concentration.”

Unlike the tests you had in school, the higher your score is, the more likely you failed.

BAC is measuring the amount of alcohol you have in your body. A high BAC has been found to negatively affect your driving ability.

It is the standard the police will use to determine if you have been committed a crime. When the amount of alcohol absorbed into your blood is found to be 8% or greater, you can be convicted of DUI (driving under the influence ).

This will result in potential jail time as well as administrative action taken against your license by the MVA. While there can be other pieces of evidence, this is the most important factor. That’s why you need to understand BAC .

The biggest factors in determining your BAC are:

  • The amount of alcohol you drank prior to being tested.
  • the percentage of alcohol in the beverage (wine has more alcohol than beer, spirits like whiskey have more than wine).
  • Your weight (the heavier you are the more alcohol it will take to raise your BAC)
  • Your sex (The body composition of men contains more water than women, so generally it will take more alcohol to raise their BAC.)
  • How long you have been drinking (drinking a lot over a short period of time will raise the BAC higher than stretching drinking over time)
  • Whether there is any food in your stomach prior to drinking.

Scientifically, Blood alcohol concentration (BAC) is the amount of alcohol present in a 100 milliliter (mL) volume of blood.

For example, 80 mg is 0.08 grams, 0.08 grams of alcohol in 100 mLs is written as 0.08%. In other words, 80 mg% is equal to 0.08% which is equal to 80 mg/dL (deciliter; 100 mLs). This value can also be described as 0.08 BAC.

As soon as your BAC passes 2%, you should be feeling the effect of the alcohol.

Here are some general effects when BAC increases:

  • .2% – Light to moderate drinkers begin to feel some effects
  • .4% – Most people begin to feel relaxed
  • .6%- Judgment is somewhat impaired
  • .08% – Definite impairment of muscle coordination and driving skills. This is the legal intoxication level in most states.
  • .10% – Clear deterioration of reaction time and control. This is legally drunk in all states.
  • .12% – Vomiting usually occurs
  • .15% – Balance and movement are impaired. Here the equivalent of a 1/2 pint of whiskey is circulating in the bloodstream.
  • .20%- Most people begin to experience blackouts
  • .30% – Many people lose consciousness
  • .40% – Most people lose consciousness and some die
  • .45% – Breathing stops. This is a fatal dose for most people.


The best means to scientifically measure your BAC is by a blood test, taking a sample from your body. If you are pulled over by the side of the road, this is not going to be practical for many reasons.

What an officer will administer instead, unless you refuse, is a breathalyzer test. This result will give you your BrAC, Breath Alcohol Concentration. If the percentage is 8% or over, like Blood Alcohol Concentration, this will give probable cause to arrest you.

Can you have a DUI defense attorney present when they give you the BAC test? In Maryland, the answer is in some situations, yes. However, your attorney must arrive within two hours of your arrest. If the lawyer does not appear in time, then it will be presumed you refused to allow the test. This will result in confiscation of your license for a minimum of 120 days, as well as whatever the outcome of the criminal trial turns out to be.

Reliability of a BAC Reading

Are breathalyzer tests that determine your BAC accurate? Generally, yes, but there are additional factors that can affect their reliability:

  • Foreign Substances – Substances present in the mouth that contain alcohol can produce “false positives” because the amount of alcohol vapor they emit may be greater than the amount exhaled from the lungs. For example, some mouthwashes, breath fresheners, and toothache medicines contain alcohol and can skew readings.
  • Calibration – Breathalyzers must be calibrated periodically, and batteries must be replaced to maintain accuracy.
  • Software – Breathalyzers run on special software, just as computers rely on operating systems, which can result in occasional bugs and glitches.
  • Human Error –  As easy as breathalyzers are to use, they still require some attention to detail.
  • Consistency – To ensure accuracy, breath tests should be performed multiple times to produce a reliable result. Breathalyzers that utilize fuel cell sensor technology provide the most reliable and accurate results in repeated tests.
  • Environmental Factors – False results can be triggered by the presence of paint fumes, varnish, and chemicals such as plastics and adhesives.

However, any potential challenge may require specific technical and legal expertise that will not be raised until there is a court hearing. You might be able to raise doubt about the test, but it will be nearly impossible to keep the BAC results from being allowed as evidence.

Other Clues for a DUI Arrest

Keep in mind that while your BAC at the time of an arrest is important, there are other factors an officer can observe about you at the time of the arrest to provide circumstantial evidence of intoxication:

  • Driving- If prior to being pulled over you were running a red light, driving excessively fast or too slowly, weaving in and out of traffic, crossing the center line, involvement in an accident. (Traffic citations for other offenses are usually what leads to the traffic stop where a DUI arrest is made.)
  • Breath- If the officer smells alcohol on your breath or notices the smell in the vehicle.
  • Appearance- If you appear disheveled, confused, unable to maintain your balance, eye contact, blurry or red eyes, redness in the face.
  • Speech- If your speech sounds incoherent or slurred, mumbling, words mixed up or difficult to make out.
  • Movement- If you have trouble walking straight or are moving overly cautiously, stumbling, awkward uncoordinated motion, or are simply unable to stand up.
  • Behavior- Unusual emotions, refusal to answer questions, inappropriate actions or remarks, sudden expected actions or movement, refusal to cooperate, outbursts, socially inappropriate actions or speech.

All or some of these factors may lead to the officer administering a field sobriety test prior to a portable breathalyzer determining your BAC. Any of these factors in and of themselves can be introduced by testimony of the officer at the time of your trial to support the claim of driving under the influence.

What if your driving doesn’t appear impaired and you don’t appear to show any ill effects of drinking when pulled over? Can you still be guilty of a DUI? The answer is yes.

If a BAC test shows you over 8% , then you can  be convicted of a DUI. If it is over 4% but less than 8% you can be found guilty of a DWI—driving while intoxicated (an offense with lesser penalties).

While DUI charges exist to prevent dangerous driving, the crime is based on your BAC at the time of arrest. Everything else is just evidence.

What if you are unconscious? Can the police perform a blood test to determine your BAC  if you don’t give consent? The Supreme Court of the United States has said in the case of Missouri vs. McNeely that taking blood from someone without their permission was a violation of their 4th Amendment right against unreasonable search and seizure.

Normally, this situation would require a warrant. The court allowed exceptions if there were an emergency or exigent circumstances that demanded immediate action to preserve evidence. Otherwise, an officer would need to get a warrant to obtain a sample of blood to test.

What if you realized you are becoming intoxicated, what can you do to reduce your BAC, so you don’t run into trouble? Not much, other than stop drinking and wait.

The only thing that will reduce the amount of alcohol in your blood is the passing of time to allow it to eventually leave your system. Eating, drinking coffee or taking a cold shower may produce other effects, but they won’t change your BAC.

That’s why there is the two-hour rule on waiting for an attorney to be with you while you take the test, because after enough time, your BAC will drop. So, the short answer is don’t drive, find alternative transportation and wait  the hours necessary for the alcohol to pass out of your body before getting on the road again.

Like any explanation, you might have additional questions, or you might want specific answers to a specific situation. If so contact Rice, Murtha & Psoras.  You’ll get answers and if you need it, you can get the representation you need.


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