Blood Alcohol Content (BAC), the medical term used for measurement of concentration of liquor in blood, is also known as Blood Alcohol Concentration. It can be denoted as a percentage by mass per volume, by mass, or a combination of both. For example, a BAC of 0.10% means 1 gram of alcohol per 1000 grams of blood. As there is a great variation in individual physiology and tolerance level to alcohol, from person to person, the number of drinks consumed is not an appropriate measure of intoxication. It varies greatly with body weight, fat percentage, and gender. Hence, neither the number of drinks consumed by a person, nor the liquor in the body, makes the precise indicator of level of intoxication. However BAC still creates a standard platform to compare the intoxication of individuals due to consumption of alcohol. Concentration of alcohol in blood can be determined by tests carried out in laboratories. However, for law enforcement investigations, it is not always possible to carry out blood sample tests for this purpose. So, Breath Alcohol Concentration (BrAC) is checked, using an instrument known as Breathalyzer. Breathalyzers estimate the percentage of alcohol found on the breath of a person. This is because spirits, once ingested, maintain equilibrium throughout the body due to their high affinity towards water. Test Assumptions The BrAC tests are carried out while assuming that the individual is an average in many ways. To understand this, let us look at the predetermined BAC average ratio. The assigned standard value is 2100:1. That means on an average, for every part of breath, 2100 parts of alcohol are found. But in actual cases, this ratio can vary from 1300 parts to 3100 parts, for every part of breath. Similarly, while analyzing urine to measure BAC, it is assumed that the average ratio is 1.3:1, although the actual proportion considerably varies from person to person. Moreover, all these tests are based on the assumption that there is complete absorption of alcohol, and it is disbursed evenly and completely throughout the body. Thus, all these tests are done by assuming that the state of equilibrium has been achieved by the body. Effects at Different Levels of BAC When ingested, the intoxication levels gradually increase with an increase in content of alcohol.

1. Euphoria: This is the initial stage of intoxication, characterized by BAC level at 0.03 to 0.12%. In this phase, a person is much more relaxed, overconfident, and appears without any inhibitions.
2. Lethargy: In this phase, BAC ranges from 0.09 to 0.23%. The person starts losing body balance, his vision gets blurred, and he appears sleepy.
3. Confusion: BAC gets increased, at 0.17 to 0.28%. Name of this phase rightly denotes the status of the person, as he appears intense in his emotions and feelings. Dizziness and nausea are peculiar to this stage.
4. Stupor: This stage is marked by the BAC count ranging from 0.25 to 0.39%, where person starts losing and gaining consciousness at frequent intervals. Due to this feature, there is high risk of coma.
5. Coma: BAC ranges from 0.35 to 0.50%. Patient becomes unconscious, his body reflexes become poor, and there is drop in his pulmonary beats, with a decrease in breathing.
6. Death: BAC exceeds the mark of 0.50%. This is a very fatal stage, marked by Central Nervous System failure.

Legal Limits Although, the effects of a particular BAC vary from person to person, it is widely used to determine the levels of intoxication. It provides a standard, common platform for a rough conclusion of the status of the subjects. Most countries have prescribed a certain level of BAC as bar, and don't allow the maneuvering of vehicles, boats, aircraft, and heavy machinery beyond these levels. Alcohol Regulation Laws differ in their limits, from one state to another. While in United States, 0.10% level is assigned for safe driving for common carriers, and 0.04% is assigned for aviators; Australia and Argentina prescribed 0.05% level of BAC. In India, the permissible limit is 40 mg/deciliter, while countries like Russia, Norway, Poland, and Sweden permit the level of 20 mg/deciliter. Countries like Saudi Arabia, Malaysia, Romania, Czech Republic, etc., are zero tolerant countries. BAC Calculation A certain mathematical approach is used to estimate the content of alcohol in blood. Although, this mathematical estimation is not as precise as a breathalyzer, it is very handy for determining the level that is not testable at a given moment. Retrograde extrapolation is one of the most used mathematical processes to calculate BAC at the time of driving. It involves consideration of rate of the absorption and elimination of alcohol, between driving and actual testing. Thus, this blood alcohol content is an important tool used by physicians, forensic experts, and law enforcement departments for varied purposes.