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Breathalyzer Accuracy

Learn about how Breathalyzer’s work

Alcohol intoxication is legally defined by the blood alcohol concentration (BAC) level. However, taking a blood sample in the field for later analysis in the laboratory was not practical or efficient for detaining drivers suspected of driving under the influence (DUI). What was needed was a way to measure something related to BAC without invading a suspect’s body. Urine tests for alcohol proved to be just as impractical in the field as blood sampling. In the 1940s breath alcohol testing devices were first developed for use by police. In 1954, Dr. Robert Borkenstein of the Indiana State Police invented the Breathalyzer, one type of breath alcohol testing device.

How do Breathalyzers Work?

We hear and read about drivers who are charged with a DUI arrest after an accident, and usually a news report on the accident will state the driver’s blood alcohol level as well what the legal limit is for blood alcohol. For example, a driver may have a BAC level of 0.15%, while the legal limit is 0.08%. But what do those figures mean and how do police officers find out if a driver they suspect has been drinking is legally drunk? You have probably heard about the Breathalyzer, but may wonder exactly how a person’s breath can show how much that person has had to drink.

Principle of Testing

Alcohol that a person drinks shows up in the breath because it gets absorbed from the mouth, throat, stomach and intestines into the bloodstream. Alcohol is not digested upon absorption or chemically changed in the bloodstream. As the blood goes through the lungs, some of the alcohol moves across the membranes of the lung’s air sacs (alveoli) into the air because alcohol will evaporate from a solution — that is, it is volatile. The concentration of the alcohol in the alveolar air is related to the concentration of the alcohol in the blood. As the alcohol in the alveolar air is exhaled, it can be detected by the breath alcohol-testing device. So instead of having to draw a driver’s blood to test his alcohol level, an officer can test the breath on the spot and determine whether there is a reason to make a DUI arrest.

Because the alcohol concentration in the breath is related to that in the blood, you can figure the BAC by measuring alcohol on the breath. The ratio of breath to blood alcohol is 2,100 to 1. This means that 2,100 milliliters of alveolar air will contain the same amount of alcohol as 1 milliliter of blood.

The legal standard in DUI law for drunkenness across the United States was 0.10% for years, but recently many states have adopted the 0.08% standard. The federal government has pushed states to lower the legal limit. The American Medical Association says that a person can become impaired when the blood alcohol level hits 0.05%. The standard 0.08% means that there is 0.08% gram of alcohol per 100 milliliters of blood.

BLOOD ALCOHOL CONCENTRATION CHART

“What is a drink?” *

One drink equals: Levels of intoxication:
1 oz. 86 proof Liquor, or BAC less than .05% – Use Caution
3 oz. wine, or BAC .05 to .079% - May be Impaired
12 oz. Beer BAC .08% & above - Presumed Under the Influence

Body
Weight
Number of Drinks
1 2 3 4 5 6 7 8 9
100  0.032  0.065  0.097  0.0129  0.0162  0.194  0.226  0.258  0.291
120  0.027  0.054  0.081  0.108  0.135  0.161  0.188  0.215  0.242
140  0.023  0.046  0.069  0.092  0.115  0.138  0.161  0.184  0.207
160  0.020  0.040  0.060  0.080  0.101  0.121  0.141  0.161  0.181
180  0.018  0.036  0.054  0.072  0.090  0.108  0.126  0.144  0.162
200  0.016  0.032  0.048  0.064  0.080  0.097  0.113  0.129  0.145
220  0.015  0.029  0.044  0.058  0.073  0.088  0.102  0.117  0.131
240  0.014  0.027  0.040  0.053  0.067  0.081  0.095  0.108  0.121

* This table shows the effects of alcohol within one hour on an average person of a given body weight. Please do not take this information as a license to drink irresponsibly. Everyone is different, and alcohol has a different effect on each person. Only you know your limits. Please drink responsibly.
*from the Arizona Department of Public Safety

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