The determination of Blood Alcohol Content (BAC) is a standardized means to measure the amount of alcohol present in brain tissue as alcohol consumption affects the brain. Because sampling of brain tissue is not practical in living people the use of blood, breath, or urine samples are used to measure the presence of alcohol in a living person. The most common means of making this determination is through the use of a breath test.
General Background on Breath Test Machines
All breath-testing devices are based on the assumption that the blood alcohol to breath alcohol partition ratio is approximately 2100:1. This is based on the premise that the amount of alcohol in 2100 milliliters of deep lung air is equal to the amount of alcohol in one milliliter of blood. This standard was adopted in 1952 as a compromise by several different companies all of whom were manufacturers of various different breath testing machines and by the National Safety Council's Committee on Tests for Intoxication. This “average” has been the subject of a great deal of debate ever since. Because the same average ratio is applied to everyone, it may be inaccurate for a particular individual, since it fails to account for differences in height, weight, and other variables unique to an individual. Despite this breath test results are recognized by law as reliable evidence.
Accuracy of Breath Test Machines
In Florida if you submit to a breath test and the results are over .08 the jurors will be instructed that they must find the defendant guilty. To defend against this your Defense Attorney’s task is to show the jury that the evidence is inaccurate. During cross examination questioning the means used to calibrate the machine, the amount of time since the machine was last calibrated prior to the test, the machine's failure rate, maintenance standards and other factors it may be possible to raise a reasonable doubt about the machine's trustworthiness.
Issues Related to Breath Tests and Blood Alcohol Levels
Absorption and Elimination of Alcohol. The active ingredient in alcoholic beverages is ethyl alcohol, or ethanol. Ethanol is not digested by the body, rather it is absorbed.
The rate at which alcohol is absorbed depends on the amount ingested along with its concentration. The contents of the digestive tract may also factor in the rate of absorption.
The rate of elimination of alcohol from the body occurs through the process of oxidation. This rate is generally accepted to be at 0.15% per hour. This is the body’s natural function and to date no realistic way of accelerating this rate has been discovered. So, no matter how much coffee you drink while you are under the influence of alcohol this will not “sober you up”, it will just keep you awake while you are under the influence.
Effects of Alcohol Consumption. While everyone is different there is a common pattern of reaction to alcohol ingestion. Initially there appears to be feelings of relaxation and pleasure which is followed by increased emotionalism and decreased psychomotor function. Excessive consumption of alcoholic beverages may result in a lot of health related issues including but not limited to liver disease, addiction and a reduced life span.
In Florida a BAC of .08% is a presumption of impairment. However factors such as body weight, tolerance of alcohol, stomach contents and other physiological variables may affect how impaired someone feels or acts. Some people may appear intoxicated at .05% yet others may not appear intoxicated at .20%.
Time Delay between Arrest and Breath Test
There is usually a considerable time delay between the time the Defendant was driving, the arrest for DUI and the actual breath test itself. After a person is stopped by the police they are usually requested to perform field exercises and then arrested and subsequently transported to a police station or a mobile Blood Alcohol Testing Unit (the so-called BAT mobile). The question then is “does the breath test prove anything other than your blood alcohol level at a police station?” However this may “open the door” to the State introducing evidence of what is known as retrograde extrapolation.
Retrograde Extrapolation
Retrograde extrapolation can be used to estimate a defendant's BAC at the time of driving based on the defendant's BAC at a known time after arrest. The basic premise of retrograde extrapolation is that the body eliminates alcohol at a certain rate. This rate varies among individuals. A mean hourly clearance rate calculated at 0.015% is utilized in retrograde extrapolation. The example below illustrates how retrograde extrapolation may be applied to a given set of facts:
By using retrograde extrapolation the prosecutor can use expert testimony to prove your BAC was higher when you were driving.
In certain circumstances retrograde extrapolation may be employed to prove the opposite, in other words that the Defendant’s BAC was below the legal limit at the time the Defendant was driving. This does require expert testimony to do this.
