Blood Alcohol Level

The blood alcohol level (BAL) or blood alcohol content is a measurement used to determine how much alcohol is in the blood. It is typically denoted by a percentage of the alcohol per volume of blood found within the body. Often the BAL may be tested for medical or legal reasons. Establishing how much alcohol a person has consumed can be useful in identifying a person’s level of intoxication. In most countries an individual can be charged with drunk driving if the BAL is above .08. Most of the states in the US have zero-tolerance laws which makes it illegal for anyone under the age of 21 to have detectable levels of alcohol in the system.

What do the different measurements define?

Each percentage expresses a level of intoxication. While alcohol will affect individuals  differently, this guideline is the standard used to identify the typical effects at each level.

  • A BAL of .05% will cause an individual to feel relaxed but will not necessarily impair regular functions.
  • A BAL of .06% will cause light headed-ness with a slight degree of impairment.
  • A BAL of .08% – .10% will affect coordination and balance and is defined as legally drunk.
  • A BAL of .15% may cause alcoholic blackouts and memory loss.
  • A BAL of .20% may cause vomiting and extreme nausea.
  • A BAL of .25% will cause significant psychological and physical effects leading to numbness or loss of feeling.
  • A BAL of .40% or more can lead to coma and/or possible death.

How does alcohol affect overall function?

Alcohol has many ill-effects which can affect an individual within a few minutes of drinking, depending on the concentration of the drink and how much is had in a particular time frame. It depresses brain activity and leads to the impairment of certain normal functions. Typically it will affect the cerebrum which controls vision, reasoning, emotion and recognition; the cerebellum which controls coordination and the medulla which controls breathing and heart rate. Therefore, once a person becomes legally drunk they are likely to experience slurred speech, uncoordinated movements or problems balancing, increased heart rate, changes in reflexes, extreme emotional outbursts, poor judgment and lowered inhibition. These effects can also occur at lower levels that are not defined as legally drunk. Women are more likely than men to experience the effects of alcohol more quickly and are more likely to get drunk below levels of .08.

What methods are used to determine blood alcohol level?

The standard testing equipment used to determine the blood alcohol level is the breathalyzer. This device allows individuals suspected of drunk driving to breathe into the machine which then detects the amount of alcohol in the blood. The air from the individual will initiate a chemical reaction which then results in a color change that will indicate the BAL.

The chemical, Potassium dichromate, found within many breathalyzer tests is yellow-orange in color. Once the vapor from alcohol contacts the crystals it changes to green with a potent green color being correlated with higher levels of alcohol. If the concentration of alcohol is found to be .08% a driver may be charged with drunk driving.

A breathalyzer test has its limits. Different factors can affect the results including the presence of natural alcohol in the body and the mouth. In addition, the use of mouth wash can exaggerate the levels of alcohol detected in the blood. Because of this, police officers often observe a person carefully. In some instances an individual may be asked to perform simple tests that can detect physical impairment before the breathalyzer is administered.

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