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What is Blood Alcohol Concentration (BAC) – How Does it Work?

What is BAC

This is Blood Alcohol Concentration (BAC)

  Blood Alcohol Concentration or Blood Alcohol Content (BAC) is an assessment of alcohol intoxication.

By measuring the alcohol concentration in a person’s blood, you get a rough measure of their impairment or intoxication. This can be used for legal or medical purposes.

  A Blood Alcohol Concentration of .05 (0.05% or 5 hundreds of one percent) means that there are 0.05 g of alcohol for every 100 ml of blood.

A BAC level of .00 means that there is no alcohol in the blood. A BAC level of .08 is known as the legal limit in United States and means that a person is legally too intoxicated to drive (Utah has adopted a legal limit of .05). For underaged drivers, all states have a legal limit that is between “any traces of alcohol” and .02, depending on state.

  Methods for testing include breath, blood, and urine tests.

Breath testing is the most common method to estimate a person’s BAC. Analysis of a blood sample for BAC is, however, generally more accurate than breath and urine tests.

  Your BAC is primarily affected by how much you drink, the time you drink, and your body weight.

The number of drinks and the time you spend drinking are the major factors affecting your BAC. But your body weight and gender also play a big role. The more you weigh, the less you will be affected by alcohol.

Women are often more affected because they generally have more body fat per pound of body weight.

Food plays a role in how quickly alcohol is absorbed by the blood and can space out the intoxication, but sooner or later all alcohol reaches the bloodstream.

Only time can sober you up -  Photo by Skitterphoto from Pexels

  BAC is raised by the amount of pure alcohol in a drink, not what kind of drink it is.

A standard drink has about 0.6 fl oz. (14 grams) of pure alcohol. This is roughly a 12 fl oz. bottle of regular beer, a 5 fl oz. glass of wine, or a 1.5 fl oz. shot of 80-proof distilled spirits.

They all contain the same amount of pure alcohol and will affect you the same way.

  Alcohol is eliminated through oxidation by the liver

Most of the alcohol is eliminated through oxidation by the liver. Only small amounts are eliminated through breathing, perspiration, and urination.

Oxidation by the liver is a slow process. To lower the BAC, you must wait for the liver to do its job. The rate cannot be increased by drinking coffee, exercising, taking a cold shower or anything else.

Read more: What helps you sober up?

In general, the liver can only oxidize one drink per hour.

How Alcohol and Your BAC Affects Driving

To understand how a few drinks affect your driving, you must understand that once alcohol is absorbed into the blood, it is transported to all parts of the body. Alcohol reaches the brain in 15 to 30 minutes. Once in the brain, alcohol affects those areas of your brain that control judgment and skill.

It is a common statement in driver manuals that “judgment is the first to go“.

Obviously, good judgment is important to driving. You must be able to judge distance, speed, and the movement of other vehicles. This ability is affected after only one drink and becomes even worse if it is dark.

Judgment also includes your attentional control. It refers to what you choose to pay attention to and what you ignore. You become more easily distracted with alcohol. Alcohol can also make you overconfident and give you a false sense of invincibility. You may start to ignore risks that you normally wouldn’t ignore.

After one or two drinks reaction times are also affected.

Since alcohol is a depressant , it slows you down. You don’t react as quickly as you normally do. The risk of ending up in a crash is much greater than if you did not drink any alcohol.

Your ability to react to hazards worsens with every drink.

  With a BAC of .10 percent, you are seven times more likely to cause a crash than if you were sober.

  As your BAC increases to .15 percent, your chances of causing a traffic crash increase to 25 times.

When Your BAC Reaches the Legal Limit

If your BAC reaches the legal limit, you are not fit to drive.

Alcohol has affected your vision and depth perception. Your eye muscles are relaxed by the alcohol and cannot focus properly.

Vision provide almost 90 percent of the information you use when you drive and any limitation in your ability to see clearly can have disastrous results.

If you drive at night, which is often the case when people have been drinking, the ability to recover from glare is also changed. If you get temporarily blinded by the headlights of oncoming vehicles, it can take many seconds before your eyes recover. For every second you drive blind, the risk of an accident is imminent.

Chances are that you still think you can drive, even though you have reached the legal limit. This is because both judgment and reasoning are affected at this stage. It is harder for you to make sense of things and apply simple logic, even if you are confident that you can.

Simply put, you are drunk when you reach the legal limit. Others may not see it and you may not be aware of it, but you are in no shape of driving.

Remember, a driver’s reaction time starts to slow at a much lower BAC. Even if you are below the legal limit, you can get a ticket if your driving is affected by alcohol and unsafe.

What is the Legal Limit

The legal limit is the BAC at which you are too intoxicated to drive safely.

The legal limit allows the state to convict you of drunk driving or driving under the influence of alcohol without any other proof of unsafe driving.

If you are stopped by a police officer who has reasons to believe that you have been drinking (reasonable cause), you will be arrested, and asked to take a test to measure how much alcohol is in your blood. If the result shows that you are at or over the legal limit, you will most likely be convicted.

Even if .08 is down from .15, which it used to be not too long ago, some experts still consider the legal limit of .08 too high. In December 2018, Utah became the first state to lower the legal limit from .08 to .05.

Many other countries set much stricter limits. It is .03% in most of India and .05% in many European countries.

Legal Limits in Other Countries (Examples)

Country Legal limit
Argentina 0.05
Belgium 0.05
Brazil 0
Canada 0.08
England and Wales 0.08
France 0.05
Greece 0.05
Iceland 0.02
India 0.03
Israel 0.024
Japan 0.03
Malaysia 0.08
Mexico .04-0.10
Nepal 0
Norway 0.02
Panama 0.08
Sweden 0.02
Thailand 0.05
Turkey 0.05


The Best Advice

Drinkers who think they can tell when they’ve had enough are very often wrong.

But alcohol affects individuals differently with many factors in the mix. The best advice is always not to drink at all if you’re driving. Or let someone who has not been drinking to drive you home.

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Quick DMV Quiz about Alcohol



Great job!

Alcohol awareness is often an important part of your DMV test. Make sure you study these chapters in your driver’s manual.

#1. How long will it take the liver to oxidize one alcoholic drink?

The liver can only oxidize about one drink per hour. Contrary to popular belief, this rate cannot be increased by drinking
coffee, exercising, taking a cold shower, taking sober-up pills or anything else.

#2. To be convicted of a DUI violation an adult's BAC level:

A BAC level below the legal limit does not necessary clear a driver from a impaired driving conviction. Remember that the law refers to alcohol, drugs, or a combination of both. If an officer have enough proof of driving under influence, you may be convicted regardless of the BAC result.

#3. Taking a cold shower after drinking alcohol:

Drinking coffee, exercising, and taking cold showers do not increase the rate of oxidation and has no effect on your BAC.

#4. Food in the stomach causes alcohol:

Food in the stomach causes alcohol to be absorbed more slowly, slowing down the rate and the level of intoxication. But remember, all the alcohol consumed eventually gets into the blood whether you have eaten or not.

#5. Which is a common effect of drinking alcohol?

#6. Which are usually the first things to be affected by drinking alcohol?

All of the above are affected by alcohol, but judgment is usually the first thing to go. Your ability to judge speed, time and distance are often altered after only one drink. In addition, your reaction time and coordination begin to deteriorate.

#7. How long will it take your body to cancel the intoxicating effects of three alcoholic drinks?

#8. The amount of alcohol in a 1.5 fl oz. shot of whiskey equals about:

The amount of alcohol in a 1.5 fl oz. shot of whiskey equals the amount in of alcohol a bottle of standard beer.

In the United States, a standard drink contains about 0.6 fl oz. or 14 grams of pure alcohol. This is roughly the amount of alcohol in:

  • 12 fl oz. of regular beer.
  • 5 fl oz. of table wine.
  • 1.5 fl oz. shot of 80-proof distilled spirits.
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DMV Tests – Check Your General Driving Knowledge

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  1. It is important to know that sober-up pills or hangover pills don’t work either. Might make you feel better. But the alcohol is still there. A waste of money!

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