This test estimates the concentration of alcohol in the blood by measuring the level of alcohol in exhaled air.
A breath alcohol test may be performed for a person who was driving or behaving erratically or was involved in a motor vehicle crash to determine if he or she was legally intoxicated at the time of the incident.
One type of this test is administered using a kit that includes a balloon and a small container filled with yellow crystals. The yellow crystals turn green when exposed to alcohol-containing air.
The person being tested is asked to exhale into the balloon. The person should fill it with one continuous breath. The balloon's mouthpiece is fitted to the end of the glass tube.
The air inside the balloon is allowed to flow through the glass tube for one minute. The alcohol content of the exhaled air is measured by counting the number of bands in the tube that have changed from yellow to green. This reflects the alcohol content of the blood.
A calibrated breathalyzer machine is also available to check a person's alcohol level. The person blows into a mouthpiece, and the machine displays the alcohol level electronically. This machine usually gives a more accurate reading than the balloon type test.
There is no preparation for this test.
Normally, blood alcohol level is zero. If the person has not been drinking alcohol, the air he or she exhales will contain no alcohol and the yellow bands in the tube will not change color. If alcohol is detected in the exhaled air, some of the yellow bands in the glass tube will change from yellow to green.
If one band is green, blood alcohol levels are .00% to .05%. If two bands are green, blood-alcohol levels are .05% to 0.1%. At these levels, the individual will suffer from reduced muscular coordination, impaired judgment, and longer reaction time due to alcohol intake.
If three bands are green, blood-alcohol levels are 0.1 to 0.15%. At this level, a person usually shows obvious signs of impairment, and is considered legally "under the influence" in all 50 states.
Some states have enacted a lower permissible alcohol limit for drivers. If the driver is under age 21, any level of alcohol in the blood is a violation of the law.