Alcohol is a drug and classified as a central nervous system depressant. It acts primarily on the central nervous system and interferes with the brain’s ability to effectively and efficiently control motor and mental functions in a person. The effect is cumulative – which means that the higher the BAC, the more numerous and severe are the effects of alcohol. These effects can be classified into three zones:
1. The Zone of Impairment (30 – 100 mg%)
A person with a BAC in the range of 30 – 100 mg% may exhibit few of the outwardly observable effects of alcohol consumption. These outward effects could be: watery and bloodshot eyes; flushed face; an odor of liquor (depending on the beverage consumed). These observable effects may occur at BACs of less than 80 mg%, but become more common as the BAC rises beyond 100 mg%. If a person was impaired by alcohol, but not intoxicated by alcohol, you might not notice anything unusual about that person (other than some of the symptoms indicated above) because the impairing effects of alcohol are inward effects. In fact, a driver who is impaired but not intoxicated might outwardly appear to be sober. The impairing effects of alcohol include: decreased comprehension, attention, and judgment leading to an impaired ability to judge the risks associated with any particular activity (such as driving), and decreased visual functions such as decreased visual acuity, depth perception, and peripheral vision. Obviously, if you were to look at a person who is impaired you could not SEE that their comprehension, judgment, and attention were affected, nor that their visual functions were diminished.
2. The Zone of Intoxication (100 – 300 mg%)
As the BAC rises beyond 100 mg%, a person becomes intoxicated by alcohol as well as impaired. At these higher BACs we start to see the signs and symptoms that most people associate with drunkenness. For the average social drinker, we see balance and speech problems starting at BACs of about 150 mg%, and for people unaccustomed to the effects of alcohol or having a low tolerance to alcohol, we see these effects at lower BACs. As the BAC increases beyond 150 mg%, the balance and speech problems become more common and more severe. At BACs starting around 200 mg%, symptoms in the average person increase to staggering gait, lurching or reeling, mental confusion, emotional instability, and problems with memory. At 250 – 300 mg%, people can become stuporous or comatose.
3. The Zone of Death (over 300mg%)
Death can occur at BACs of 300 mg% or more due to depression of the respiratory centre of the brain.