Understanding Blood Alcohol
Blood Alcohol Concentration (BAC) is the amount of alcohol in a person’s body measured by the weight of the alcohol in a certain volume of blood. Alcohol is absorbed directly through the walls of the stomach and into the small intestine, thereafter it moves its way into the bloodstream, and travels throughout the entire body and ultimately into the brain. Studies have shown that alcohol quickly absorbs into the body and can be measured within 30 to 70 minutes after a person has had an alcoholic beverage.
Contrary to popular myth, medications or drugs will not directly change one’s BAC level. However, if someone drinks alcohol while taking certain medications, he may feel – and actually may be – more impaired, which obviously may affect his ability to perform driving-related tasks. Because of the multitude of factors that affect BAC levels it is very difficult to assess one’s own BAC level or even his own level of “impairment”. Though small amounts of alcohol can affect one’s brain and the ability to drive, people often swear they are “fine” after several drinks; failure to recognize one’s alcohol impairment is often deemed a common symptom of impairment.
While the lower stages of alcohol impairment may be undetectable to others, the drinker knows vaguely when the “buzz” begins. It is said that a person will likely be too impaired to drive before looking or even feeling “drunk.” In Washington State, drivers can be arrested with a BAC below .08 if a law enforcement officer has probable cause to believe an individual is driving while under the influence of alcohol and/or drugs.
The following chart contains common symptoms and the probable effects on driving abilities at various BAC levels:
| BAC Level | Typical Effects | Effects on Driving |
|---|---|---|
| .02% | Some loss of judgment; Relaxation; Slight body warmth; Altered mood. | Decline in visual functions (rapid tracking of moving target); Decline in ability to perform two tasks simultaneously. |
| .05% | Exaggerated behavior; Loss of small-muscle control; Impaired judgment; Lowered alertness. | Reduced coordination; Reduced ability to track moving objects; Difficulty steering. |
| .08% | Poor muscle coordination (balance, speech, vision); Harder to detect danger; Impaired reasoning. | Concentration loss; Short-term memory loss; Speed control issues. |
| .10% | Clear deterioration of reaction time and control; Slurred speech; Slowed thinking. | Reduced ability to maintain lane position and brake appropriately. |
| .15% | Far less muscle control than normal; Major loss of balance; Vomiting may occur. | Substantial impairment in vehicle control and auditory information processing. |
Source: Information gathered from NHTSA, NIAAA, AMA, and the National Commission Against Drunk Driving.
Field Sobriety Testing
Law enforcement agencies in Washington State often use Field Sobriety Testing to assist them in determining impairment. There are only three field sobriety tests recognized as valid “standardized” tests by the National Highway and Traffic Safety Administration (NHTSA):
- (1) The Horizontal Gaze Nystagmus (HGN) test
- (2) The Walk and Turn (WAT) test
- (3) The One Leg Stand (OLS) test
HGN (Horizontal Gaze Nystagmus) looks for involuntary jerking of the eyeball:
- Jerking of the eyeball at rest or while following a stimulus.
- Distinct and sustained nystagmus at maximum deviation.
- Jerking as the eyeball moves to the side before it gets to a 45-degree angle.
WAT (Walk and Turn) is a divided attention test. Officers look for eight specific clues:
- Cannot keep balance during instruction; Starts too early; Stops walking; Misses heel-to-toe; Steps off line; Raises arms (more than 6 inches); Incorrect number of steps; Improper turn.
OLS (One Leg Stand) requires the subject to raise a leg six inches and count aloud. Indicators include:
- Swaying while balancing; Using arms for balance; Hopping; Putting the foot down.
