What is Blood Alcohol Concentration?

Blood alcohol concentration refers to a measurement of a person’s level of intoxication. This measurement is obtained by assessing the amount, by volume or mass, of alcohol in the bloodstream. The term blood alcohol concentration is often shortened to BAC and used for legal purposes. In many jurisdictions, driving under the influence (DUI) laws are based on setting a maximum BAC for the operators of motor vehicles.

Blood alcohol concentration measures how intoxicated a person is at a given time. The results can do a great deal of fluctuating even within the course of a day. The more alcohol a person consumes, the higher his BAC should be. If he stops consuming alcohol, his BAC may still continue to rise because some of the alcohol consumed earlier may not have been absorbed into the bloodstream at the time of the initial testing. Eventually, if consumption is discontinued, the level of alcohol in the blood should begin to drop, resulting in a lower blood alcohol concentration.

BAC is often expressed as a percentage due to the manner in which it is measured. The same method of measurement is not used globally. It is most common to calculate blood alcohol concentration in terms of either the mass or volume of alcohol present in a specific amount of a person’s blood.


In many jurisdictions, drunk driving laws are established based on blood alcohol concentration. What tends to happen in these instances is that the law will specify a legal limit, normally expressed as a percentage. If a person is caught operating a vehicle and her blood contains that percentage or higher, she may be arrested and charged with drunk driving.

For example, in the United States, it is illegal for a person to operate a motor vehicle if he has a BAC of 0.08 or higher. In some cases, this maximum may be lower. These laws are often so strict that even if the person does not feel or act drunk and he was operating the vehicle properly, he can still be convicted.

One reason that BAC is used for DUI enforcement is because it is believed that this measurement can assess the risk of a person having a car accident. Legislation is often based on studies that report that the higher a person’s blood alcohol concentration, the more she loses control of her cognitive functions. These include abilities such as eye and hand coordination, which are important for the safe operation of a motor vehicle.



Discuss this Article

Post your comments

Post Anonymously


forgot password?