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What is Blood Alcohol Concentration?

Posted by:

James Clark | December 20, 2018

Blood alcohol concentration, commonly referred to as BAC, determines an individual’s level of intoxication. It’s a measure of the percentage of alcohol that exists in one’s blood and is shown as a ratio of alcohol to blood in the body. For reference, someone with no alcohol in their system will have a BAC of 0.00. 

Having a system in place for assessing an individual’s ‘drunkness’ has allowed states to create laws and policies around what people can and cannot due under the influence. For example, in a collective effort to reduce fatalities on the road, all 50 states agreed to enforce a BAC for drivers of 0.08% in 2004. Which means that anyone 21 and up is considered legally intoxicated and unable to drive safely when 8/10ths of a milliliter of alcohol is found present in every 1000 milliliters of their blood.  Sounds complicated, but it typically only takes a couple drinks to hit that limit. 

Now, you might be wondering, how does one determine a person’s BAC level?

How is BAC measured?

The amount of alcohol in a person's body is measured by the presence of alcohol in a certain volume of blood. This is called the blood alcohol concentration, or "BAC." A driver's BAC can be measured by testing the blood, breath, urine or saliva. Law enforcement use breath testing as their primary method because it’s quick, reliable, and impossible to trick. 

BAC highly correlates to the amount of alcohol consumed over time. However, it’s important to keep in mind that BAC is also influenced by other factors such as weight, the rate that alcohol is consumed, gender, age, and much more. For example, women typically become intoxicated more quickly than men that drink the same amount over the same period of time, even if body weights are the same. 

Restaurant staff and bartenders are also among those who usually have BAC education as part of their training. In fact, it’s normal for establishments who offer alcohol to have a chart behind the bar that displays estimates of a person’s BAC level based on height, weight, duration, and amount of alcohol consumed.

The chart helps the staff, primarily the bartender, in making calculated judgement on customers’ intoxication levels.

Other Factors that Affect BAC:

  • The person’s gender
  • Drinking on an empty stomach
  • The rate that he person’s drinking
  • Ratio of body fat (body fat does not absorb alcohol)
  • Metabolic rate (affected by diet, digestion, fitness, emotional state, hormonal cycle, time of day, year etc).
  • Tiredness also affects concentration and absorption.
  • Individual differences in size, weight, and metabolism.
  • The percentage of alcohol in the drink.
  • Type of alcohol (fizzy drinks are absorbed more quickly).
  • The amount of time since the last drink (the body can only break down about 1/2 a drink an hour).

The use of stimulants, such as caffeine won’t affect BAC, but may ‘mask’ the effect of alcohol, making you feel more sober than you really are.

What are the risks of having a high BAC?

The faster someone drinks, the higher the BAC is, and the more dangerous drinking becomes. Here’s an overview of how alcohol consumption can affect a person based off different BAC levels:

  • BAC .02 – Drinkers begin to feel moderate effects.
  • BAC .04 – Most people begin to feel relaxed, mildly euphoric, sociable, and talkative.
  • BAC .05 – Judgment, attention, and control are somewhat impaired. Ability to drive safely begins to be limited. Sensory-motor and finer performance are impaired. People are noticeably less capable to make rational decisions about their capabilities (for example, about driving.)
  • BAC .08 – This is legal level for intoxication in some states. There is a definite impairment of muscle coordination and driving skills.
  • BAC .10 –This is legally drunk in most states. There is a clear deterioration of reaction time, control, and hand-eye coordination. 
  • BAC .12-.15 – Vomiting usually occurs, unless this level is reached slowly, or if an individual has developed a strong tolerance to alcohol. In addition:
    • Drinkers are drowsy.
    • Drinkers display emotional instability, loss of critical judgment, impairment of perception, memory, and comprehension. Lack of sensor-motor coordination and impaired balance are typical.
    • Decreased sensory responses and increased reaction times develop.
    • The vision is significantly impaired, including limited ability to see detail, peripheral vision, and slower glare recovery.
  • BAC .15 – This blood-alcohol level means the equivalent of 1/2 pint of whiskey is circulating in the blood stream.
  • BAC .18-.25 – Drinkers are disoriented, confused, dizzy, and have exaggerated emotional states. Vision is disturbed, as is perception of color, form, motion, and dimensions. Drinkers may also experience increased pain threshold and lack of muscular coordination. Furthermore, they may stagger or lose the ability to walk and have slurred speech. Apathy and lethargy are typical.
  • BAC .25-.30 – Drinkers display general inertia, near total loss of motor functions, little response to stimuli, inability to stand or walk, vomiting, and incontinence. Drinkers may lose consciousness or fall into a stupor.
  • BAC .30-.50 – Symptoms are complete unconsciousness, depressed or absent reflexes, subnormal body temperature, incontinence, and impairment of circulation and respiration.

Death may occur at .37% or higher, while BACs of .45% and higher are fatal to nearly all individuals.

Using BAC Awareness to Maintain Order at the Bar

A strict alcohol program must ensure certification of all servers through a state-sanctioned alcohol-awareness training program. After that, it’ll be on the management team to lead by example and enforce the rules and standards without exception. Making responsible service as part of the culture, will help the establishments avoid any penalties and negative publicity going forward.

A few best practices to consider when examining your responsible service policy are:

  • Outlining a clear procedure for refusing service.
  • Having standard recipes for bartenders and servers to follow.
  • Training all your staff (i.e. hosts, valet, bussers, etc.) in addition to the bartenders and servers.
  • Communication system between management and other servers when someone is suspected to have over consumed.
  • Implementing closing procedures including “last call,” evaluate customers’ intoxication level, and providing alternative forms of transportation.

Identifying BAC levels can be very tricky for those without prior experience. Thus, aside from training, an accessible support system that may come in the form of documents, charts, or tools, must be available for all the staff who are serving alcohol.