Get Herald RSSSenator Barack Obama! Okay, now that we've got your attention, we would like to introduce ourselves. We're two curious seniors who are inspired by the many unanswered questions that arise each year at Brown and decided to do something about it. This week, prompted by a series of alcohol-related events, we are tackling blood alcohol limits and their relationship to drunk driving.
Concerns about the effects of drinking go back thousands of years. Ancient Greek mythology has it that Dionysus, god of wine, when affronted by a mortal, took vengeance on a young girl, Amethyst. The goddess Diana protected Amethyst by turning her into a white quartz statue which Dionysus spilled his wine on, turning the quartz into the purple stone known today as amethyst.
Amethysts, from the Greek meaning "not" (a-) and "make drunk" (methyskein), were commonly thought to ward off the effects of drunkenness.
This summer, the Amethyst Initiative, a group of more than 100 current and former college presidents, released a statement declaring their intention to rethink the drinking age in order to combat bingeing and other detrimental effects of alcohol use.
Mothers Against Drunk Driving, one of the main opponents to the Amethyst Initiative, has focused the debate on drunk driving, an issue that hit close to home in June when a former chef for Ruth Simmons was pulled over with a staggering blood alcohol content of .49 percent. So what exactly is blood alcohol content and how is it measured?
Blood alcohol content is a measure of the concentration of alcohol by mass in the blood stream. As of August 2005, the nationwide BAC limit for an adult operated vehicle was .08 percent, or .08 grams of alcohol per 100 milliliters of blood, while for underage drivers, the limit varies across states from 0 percent to .02 percent (Rhode Island uses a .02 percent limit).
By most standards, this limit is somewhat lenient on drivers. By about .02 percent, most people have a reduced capacity to focus, but are generally relaxed and competent drivers. As the BAC increases from .05 percent to.1 percent, so does one's inability to react to novel situations and execute the coordinated maneuvers driving requires. Studies have shown that, at a .08 percent BAC level, a single vehicle accident is 11.1 times more likely than for a sober driver.
While the concentration of alcohol in the blood is a fair, though somewhat indirect measure of intoxication across various groups, there exist a wide variety of factors relating the amount of alcohol consumed to one's level of intoxication.
With more blood, food, water or acquired metabolic enzymes, the body can handle more alcohol before getting drunk; in a typical college population then, anywhere from two drinks (for a petite, female, infrequent drinker for instance) to five drinks (for an overweight, male, heavy drinker) over the course of an hour can push you over the legal BAC limit.
Behavioral tolerance is one outcome of habitual drinking not accounted for in a BAC evaluation. Drinkers who repeatedly perform a behavior while intoxicated, such as driving from Fish Co. to Keeney, can learn to adapt this behavior to their altered mental state -- making them better drunk-drivers. That is to say, the coordinated tasks of braking, steering, and changing lanes can be improved by a behavioral tolerance, but certain other aspects of driving, such as reacting to a person stepping out from behind a parked car, cannot be accommodated.
When police happen upon a swerving, or irregularly slowing or accelerating car, they turn to breathalyzers to enforce the BAC limit. These devices rely on an even more indirect method of gauging intoxication than BAC: measuring breath alcohol content and inferring BAC.
This inference can be justified through the empirical observation made by chemist William Henry: that at a given temperature, the concentration of a gas (alcohol in this case) dissolved in a volume of liquid (blood) is proportional to the partial pressure of that same gas in equilibrium with the liquid. So breathalyzers can show a relationship between alcohol pressure in one's breath and one's BAC.
Converting breath alcohol readings to blood alcohol percentages can be tricky. Modern breathalyzers use as their constant of proportionality the ratio 2100 parts BrAC to 1 part BAC; studies have shown, however, that these ratios vary across individuals from 600:1 to 3000:1. The deviation can be attributed to the several independent elements of William Henry's Law. For example, blood isn't a pure liquid. Red blood cell volume varies greatly from person to person and the body's temperature fluctuates with ambient temperature and metabolic rate.
The equilibrium that exists between the blood alcohol and the vapor alcohol in the airway - the determining factor in the test - can be affected by breathing pattern. That a DUI can be narrowly avoided by hyperventilating after being pulled over seems to undermine this decades-old method of enforcement.
As a final note, while we really enjoy explaining how stuff works, we certainly do not endorse any kind of alcohol abuse, especially drunk driving. Don't sue.
Want something explained? Ask the Wiz Kids at AskTheWizKids@browndailyherald.com.
