The term BAC refers to the concentration of alcohol in a person’s system. Measuring the amount of alcohol, or ethanol, in a person’s system requires a blood, saliva, urine, or breath sample.
An alcohol breath test refers to BAC measurement through breath. This test will typically require a person to blow into a device known as a breath analyzer, or breathalyzer Trusted Source, which is usually portable.
An individual can use a personal device to measure their own BAC. However, it is more common for law enforcement to request a breathalyzer test if they suspect that a person has been drinking alcohol and not complying with a drinking-related law, such as driving under the influence of alcohol.
A breathalyzer test measures BAC, which reflects the percentage of alcohol in a person’s blood. Authorities can use BAC levels to gauge a person’s level of intoxication. Following alcohol consumption, the body absorbs this chemical through the stomach lining into the bloodstream. As blood passes through the lungs, some alcohol evaporates and moves into the lungs.
The concentration of alcohol in the lungs relates to the concentration present in the blood. By using a partition ratio, it is possible to determine the BAC almost instantly from the air a person exhales rather than requiring a blood sample. The ratio of breath alcohol to blood alcohol is roughly 2,100:1. This means that roughly 2,100 milliliters (ml) of breath will contain the same amount of alcohol as 1 ml of blood.
Using the partition ratio, a breathalyzer can calculate a person’s BAC. Generally, a breathalyzer is able to measure BAC due to a chemical reaction. The alcohol vapor in a person’s breath reacts with an orange solution known as potassium dichromate. When alcohol is present, this solution turns green. This color change creates an electrical current, which the breathalyzer can convert into a value to determine the BAC.
Generally, the BAC limit in the U.S. is 0.08%. However, in Utah, the limit is 0.05%. For an adult, a BAC of 0.08% may correspond Trusted Source to consuming four or more drinks — typically five or more drinks for a male — in 2 hours. If a person’s BAC measures 0.08, it means that there are 0.08 grams of alcohol per 100 ml of blood or that their blood is 0.08% alcohol.
The following chart summarizes different BAC levels and their potential effect on a person’s perceptions and capabilities.
| BAC level |
Effect on perceptions and capabilities |
| 0.01–0.05 |
relaxed, a slight “buzz,” less inhibited, and alert |
| 0.06–0.10 |
emotional, numb, sleepy, reduced memory and coordination |
| 0.11–0.20 |
mood shifts, mania, inappropriate behavior |
| 0.21–0.30 |
aggression, depression, impaired vision and reasoning |
| 0.31–0.40 |
unconsciousness or coma |
| 0.41 and over |
potentially fatal |
Generally, there are two different types of breath analyzer tests: preliminary alcohol screening (PAS) tests and evidential breath tests (EBTs).
PAS tests refer to the small handheld devices that police may use in the field to determine a person’s BAC. However, these machines are not always accurate. EBTs describe larger, stationary machines that are more reliable, which the police keep at the jail or station. A law enforcer may use a PAS machine prior to an arrest and then an EBT after the arrest to confirm the results.
Breathalyzers may also use different techniques to measure BAC. These can include:
electrochemical fuel cell breathalyzers
infrared optical sensor breathalyzers
semiconductor breathalyzers
Ongoing research is also developing breathalyzers that are compatible Trusted Source with smartphones and looking at other ways to measure intoxication using smart devices.
