Final answer:
A person of 21 years or older is considered under the influence of alcohol with a blood alcohol concentration of 0.08% or higher. Alcohol intoxication levels are measured using devices such as Breathalyzers, and metabolism rates of alcohol can vary individually.
Step-by-step explanation:
A person 21 years of age or older is considered under the influence of alcohol if the person's blood alcohol concentration (BAC) is 0.08% per 100 mL of blood. This level of BAC is typically reached after the consumption of two or more alcoholic drinks. Factors such as age, sex, and pre-existing health conditions can influence individual BAC levels even with the same amount of alcohol consumed.
The legal definition of alcohol intoxication with a BAC greater than 0.025-0.080% can be measured via blood or breath testing, with devices such as a Breathalyzer playing a crucial role in this determination. The Breathalyzer device measures the ethanol concentration in a person's breath, which correlates to the blood alcohol level. The rate at which alcohol is metabolized in the body is approximately 15 mg/dL per hour, but this can vary depending on individual factors.