Blood Alcohol Content (BAC) and Florida Law

Blood alcohol content (BAC), also called blood alcohol concentration, blood ethanol concentration, or blood alcohol level is most commonly used as a metric of alcohol intoxication for legal or medical purposes. BAC is usually expressed as a percentage of alcohol (generally in the sense of ethanol) in the blood. For instance, a BAC of 0.10 means that 0.10% (one tenth of one percent) of a person's blood, by volume is alcohol.

There are five different bodily samples that can be screened for a DUI suspect's BAC level: urine, saliva, hair follicles, blood and breath. However, only breath analysis (i.e. breathalyzer test) and blood screening are usually used by law enforcement for gathering evidence. Since blood screening is considered more invasive, this method is used less often than breath analysis (mainly after a serious accident or where the suspect has refused a breath test). A blood test gives much more accurate results of blood alcohol content than a breathalyzer test.

There are several different machines on the market used for analyzing a DUI suspect's BAC. The most current generation of breath analysis machines (still commonly referred to as "breathalyzers"), analyze the alcohol content of exhaled vapor through a method called infrared spectroscopic analysis. The latter method of analysis is based on the scientific principal that captured alcohol vapor absorbs light waves of a particular frequency in the presence of light, depending on the amount of alcohol present. A computer translates this data into the more familiar BAC measurement used to determine the level of alcohol in a person's bloodstream.

Breathalyzers have been considered acceptably accurate by most courts as tools for gathering evidence. However, some independent studies have determined that breath readings can vary by 15% from actual BAC levels (as measured by a blood test). Some courts have even thrown out breathalyzer results, calling into question the reliability of the machines. Problems with the breathalyzer machine include:

• High readings due to design flaws;
• Variance in results based on the temperature of the machine itself;
• Different results from the varying body temperatures of test subjects; and
• Variances in the presence of hematocrit in the blood also affecting test results.

Several years ago, every state had a different BAC level to determine when a driver would be charged with a DUI. With the number of deaths by vehicle on the rise due to alcohol-related incidents, another countermeasure was needed in the fight to stop drunk driving. The nation as a whole began a campaign to persuade states to lower their limit to a standard of 0.08. Since the lowering of the limit, the number of DUI's has decreased. When tests reveal that a suspected DUI driver has a BAC that is extremely high (the Florida enhanced penalty aggravated BAC limit is .15%), the crime becomes an aggravated DUI and will likely result in a harsher punishment. If you are underage, there is a zero tolerance BAC limit of .02%.

According to Florida Statute 316.1934, (see www.flsenate.gov if you would like to read the entire statute) it is illegal for any person who is under the influence of alcoholic beverages or controlled substances, when affected to the extent that the person’s normal faculties are impaired, to drive or be in actual physical control of any motor vehicle within the state of Florida. Such normal faculties include, but are not limited to, the ability to see, hear, walk, talk, judge distances, drive an automobile, make judgments, act in emergencies, and, in general, normally perform the many mental and physical acts of daily life. The results of any test administered in accordance with Florida Statute 316.1932 or Florida Statute 316.1933 and this section are admissible into evidence, and the amount of alcohol in the person’s blood or breath at the time alleged, as shown by chemical analysis of the person’s blood, or by chemical or physical test of the person’s breath, gives rise to the following presumptions:

(a) If there was at that time a blood-alcohol level or breath-alcohol level of 0.05 or less, it is presumed that the person was not under the influence of alcoholic beverages to the extent that his or her normal faculties were impaired.

(b) If there was at that time a blood-alcohol level or breath-alcohol level in excess of 0.05 but less than 0.08, that fact does not give rise to any presumption that the person was or was not under the influence of alcoholic beverages to the extent that his or her normal faculties were impaired, but may be considered with other competent evidence in determining whether the person was under the influence of alcoholic beverages to the extent that his or her normal faculties were impaired.

(c) If there was at that time a blood-alcohol level or breath-alcohol level of 0.08 or higher, that fact is prima facie evidence that the person was under the influence of alcoholic beverages to the extent that his or her normal faculties were impaired. Moreover, such person who has a blood-alcohol level or breath-alcohol level of 0.08 or higher is guilty of driving, or being in actual physical control of, a motor vehicle, with an unlawful blood-alcohol level or breath-alcohol level.

These presumptions do not limit the introduction of any other competent evidence bearing upon the question of whether or not the person was under the influence of alcoholic beverages to the extent that his or her normal faculties were impaired.

Factors that affect BAC include:

• How many drinks you have
• Food eaten along with drinking alcohol will result in a lower, delayed BAC because the alcohol enters the bloodstream at a lower rate
• Alcohol is attracted to areas of the body with a lot of water. Fat contains very little water, and allows more alcohol to enter the blood stream.
  • A person with lower percent of body fat will generally have a lower BAC than a person with a higher percent of body fat.
  • Women tend to have a higher percentage of fat and a lower percentage of body water. Therefore, if a man and a woman of the same weight ingest the same amount of alcohol, the woman will tend to have a higher BAC.
  • Muscle contains a lot of water. People who are more muscular tend to have lower BACs.
• Drinking when you are tired can lead to a higher BAC because your liver does not function as well when you are tired.
• When you’ve been sick or are currently sick, you will be dehydrated. Dehydration has a number of effects that cause greater intoxication.
• Only time can lower your BAC. Coffee, cold showers, and jogging around the block will just leave you alert, wet, and out of breath.

 If you want to estimate how much you can drink without exceeding the legal limit of .08, go to www.ou.edu/oupd/bac.htm and answer the questions. The blood alcohol calculator will estimate how much alcohol will be in your blood after drinking a specific number of specific drinks. This will help you know when to stop drinking if you know you must drive home.

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