Final answer:
Legally, a person is considered impaired with a Blood Alcohol Concentration (BAC) at or above 0.08%. This legal limit is widely recognized in the United States for determining when an individual is not fit to drive due to the influence of alcohol.
Step-by-step explanation:
When discussing the point at which someone is legally impaired by alcohol, we refer to their Blood Alcohol Concentration, often abbreviated as BAC. In the United States, a person is considered legally impaired and it is illegal to drive with a BAC at or above 0.08%. This is because a BAC at this level signifies that alcohol has affected the individual's motor skills, reaction times, and judgment sufficiently to impair their ability to operate a vehicle safely.
It's important to note that individual reactions to alcohol may vary, but legally, the impairment threshold has been set at this level by law. The BAC can be measured through breath, blood, or urine testing. Remember that the only effective way to avoid alcohol toxicity and reduce BAC is to give the liver enough time to metabolize the alcohol; activities such as drinking coffee or taking a shower do not expedite this process.