Explaining Blood Alcohol Levels (BAC) (What does the .08% BAC mean? How many drinks is that?) STAFF PICK

Posted almost 4 years ago. Applies to Austin, TX, 5 helpful votes

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BAC Blood Alcohol Concentration Levels Overview & Explaination for Austin DWI Arrests

Blood alcohol concentration levels, or BAC, is a number typically expressed in a percentage that references the concentration of alcohol within the blood stream. Since alcohol is dissolved evenly in the fluids of the body, rather than body fat, a high level or concentration of alcohol within the body, specifically the blood stream, will begin to affect motor skills and thought reflexes. The higher the concentration of alcohol in the blood stream, the more a person will be affected.

Early studies into the way alcohol is absorbed into the body and blood alcohol concentration levels were conducted in a series of research experiments by Widmark, who devised a basic formula for calculating BAC, Blood Alcohol Concentration. The formula is still widely used by lab technnitions for the district attorney's office who testify as expert witnesses at DWI Jury Trials. The Widmark Formula can be expressed in a long or short form. Many so called expert witnesses attempt to only use the short form, which can lead to inaccuracies in the calculation; even the long form of Widmark's formula is not 100% accurate, and should only be used as a guide rather than hard science or fact.

The Basic Widmark Formula is as follows: %BAC = (A x 5.14 / W x r) - .015 x H

"A" is the total number of ounces of alcohol ingested by the individual starting at the first drink.

"5.14" is a mathematical conversion factor (.823x100/16) used to convert liquid ounces to regular weighted ounces, with the "100" used to convert the final value to a percentage, and lastly, "16" is used to convert lbs to ounces.

"W" stands for the weight of the individual consuming the alcohol, while "r" is the distribution ratio for alcohol through the body. For men, "r" stands for 0.73, while for woman the value is 0.66.

Lastly, "H" is the period of time, in hours, that alcohol was eliminated from the body -- in other words, how quickly the alcohol finished going though the bloodstream and then was processed by the liver, thereby losing the potent affect of the alcohol itself. Typically, "H" is equal to the time btween the first drink and the time the BAC calculations are being made (typically the time of driving).

Key to BAC levels and the Widmark Formula is the idea that all people share the same or very similar parameters for alcohol absorption and elimination through the body. This includes distribution of alcohol through the bloodstream, meaning how long it takes a drink to work its way through your body before the BAC reading will reach it's true mark. While rough estimates place people at the same values for each of these traits, the truth is that people vary in each phase of BAC calculations, and involves a number of other factors that cannot be ignored.

Such factors that need to be accounted for include the hours of sleep an indiviudual has had the night before, whether they are on any medications, if they are ill or suffer from certain ailments, if a person ate, and if so, how much and how long ago, and whether the person was drinking other fluids in addition to the alcohol.

Also, some people's body flushes alcohol out faster than others, which can lead to individual tolerance differences. It is sometimes acecpted for basic calculations to say a person can burn off or eliminate alcohol at a rate of 0.02% per hour elimination phase rate, however, the rate of an individual's metabolism can vary significantly, leading to inaccuracies in DWI expert witness testimony. This means if an individual is at a .04% BAC, and falls within the normal range for elimination, that person would require two hours of no drinking to reach 0.0%, however this is a ROUGH ESTIMATE.

The equasion for estimating an individual's rate of alcohol elimination and burn off (Alcohol Metabolism Rate) is as follows: BAL (at xx minutes after drinking) = BAL - Alcohol destroyed after xx minutes).

It is helpful, but not necesary to convert the amount of alcohol consumed (usually measured in ounces or descriptive terms like mug (8oz) or pint (16oz)) in mLs. For example, one 12oz beer is equal to 13,500 mLs.

Also helpful, is to think of drinks in terms of the percentage each one will reach upon absorption into your body. For example, a common beer like budweiser, which contains about 4.5-5% alcohol volume per can/bottle, will give the "Normal" consumer about a 0.02% reading of BAC after about 45 minutes of consumption. If the drinks following are consumed faster than one drink per hour, the BAC levels will climb higher, depending on the persons weight, age, drinking habits and tolerance, meals, other liquids, metabolism and burn off elimination rate, and medications, sleep, hereditary issues and illnesses.

Because there are so many other factors that go into calculating a person's BAC at the time of driving, it is imperative for an investigator or scientist to fully examine the individual's medical history and lifestyle habits, recording any details for inclusion in the BAC analysis for a DWI. However, expert witnesses for the prosecution rarely if ever attempt to obtain the information needed for a detailed and accurate analysis of BAC levels, instead relying on the data of an average person, hoping the data will be reliable enough.

For your DWI, or your loved one's DWI trial, "close enough" should never be acceptable. Make sure you speak with an attorney who knows DWI law and DWI Defense well enough to expose the expert DWI witness on the stand and demonstrate the incomplete analysis to the jury. Call us Today for a Free DWI Case Evaluation.

Explaining Blood Alcohol Levels (BAC) (http://www.lawofficeofrobertkeates.com/dwi/explaining_bac.php) (What does the .08% BAC mean? How many drinks is that?)

Additional Resources

View our DWI / DUI Legal Guide at: http://www.lawofficeofrobertkeates.com/dwi/dwi_guide.php

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