Minutes after drinking, alcohol can be measured in the blood. Levels of alcohol in the blood are easily measured for numerous reasons--the primary one being able to determine whether blood alcohol content (BAC) has reached the legal limit.

Factors affecting blood alcohol content are food consumption, which will slow the absorption of alcohol into the bloodstream, size and weight of the drinker, and the amount consumed over a period of time. As amounts diminish and are expelled from the system, time is a critical factor in amounts of alcohol left in the blood.

Legal Limits from State to State

Nationwide, the legal BAC limit is .08, the amount proven to impair judgment. Reaction time is slowed significantly at this amount, as is attention span and the ability to multi-task. Because ALL behaviors are heavily impacted by this amount of consumption, this is the legal limit for any type of activity performed, especially driving.

Data confirms that aggressive behaviors are present for drinkers have BAC of .08 or higher, thus reminding us that 40-60% of those incarcerated nationwide are convicted of crimes committed under the influence of alcohol at this rate or higher. This applies to employment, which can also be tested randomly, as well as performing publicly in any means, such as being arrested for “public intoxication.” If there is any reason for law enforcement to intervene on someone in a public place, this limit will be legally enforced. Also when boating, swimming, motorcycles, skiing, and use of any kind of equipment that requires skillful operation, such as tools.

Methods of Testing

Blood alcohol content is tested through a blood sample, via a saliva sample, a urine sample, or by breath analysis. Many factors determine the level of alcohol in a person’s blood. Laws regarding legal quantities of alcohol present in the blood of someone operating machinery or a vehicle have been adapted over the years to accommodate what is legally “drunk” or “under the influence” nationwide in the US.

Ingestion/Intoxication Levels

Behavior is affected for everyone drinking alcohol, not just when an intoxication level is reached. While no set behavioral patterns occur, there are certain physical, emotional, and physiological effects that are common with alcohol consumption. The following information is taken from the table, Characteristic Effects of Different BAC Levels, by Dr. William R. Miller which illustrates how increasing amounts of alcohol affects behavioral patterns.

BAC Level Expected Behavioral Effects

  • .02-.04 Relaxation, mild euphoria, relaxed social behaviors
  • .055 Any positive changes occur below this limit. Judgment altered...driving and motor abilities impaired” lack of coordination, “information processing impaired, loss.
  • .06-.08 of restraint, fantasies and motivation change.
  • .10 Legally intoxicated in all states; reaction time slowed, memory impairment, increased risk of fatal car crash by 10x.
  • .12 Vomiting may occur unless tolerance established.
  • .15 Balance impaired, slurring of speech, fatal crash increases to 25x at this BAC; Major memory impairment “blackout” normally occurs in this range (complete memory loss).
  • .20 Memory does not transfer from short-term to long-term storage.
  • .30 Double vision may occur; most drinkers become unconscious or fall asleep.
  • .45 Lethal dose for 50% of adults; death occurs by alcohol poisoning - central nervous system inhibition of heart and breathing.

How Many Drinks until Intoxicated?

Alcohol levels in the blood of the drinker are different, due to several factors. The amount consumed and the time period over which it is consumed. A person drinking four 1-ounce drinks in 30 minutes will have higher blood alcohol content than a larger person consuming the same four drinks over 2 hours. Some people absorb alcohol more rapidly, due to having not eaten, having a smaller body mass, or other health factors, especially taking medications impacting the effects of alcohol and increasing behavioral aspects.

Women absorb alcohol differently than men, being inclined to reach higher blood levels of alcohol on less. Their capacity is less, even when the same size as the man. Absorption of alcohol happens faster and at a higher blood-alcohol ratio. Once believed to be due to body fat, it is now known women do not have the same number of digestive enzymes in their stomachs to help metabolize alcohol.

Highest rates of alcohol occur within an hour. It takes approximately one hour for each ounce of alcohol consumed to be processed out of the drinker’s body via the liver. While some of the alcohol is removed through respiration or the kidneys, 90% goes through the liver. Depending on the type of alcohol and amount, ridding the body completely takes several hours, of 100 proof liquor, 2.5 ounces of wine, or 10 ounces of beer.

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