Science Of Breath Testing; Theory Of Fuel Cells - Intoximeters Alco-Sensor FST Operator's Manual

Alco‐Sensor FST®
2.5 Science of Breath Testing
When a person consumes an alcoholic beverage, it passes from the mouth and esophagus to
the stomach and small intestine, where it is absorbed into the blood stream. The absorption of
alcohol is quite rapid, generally taking 20 to 30 minutes after consumption to reach the
maximum reading. Absorption time may be affected by the type and amount of food in the
stomach, the rate of alcohol consumption, the type of beverage consumed as well as some
drugs, disease and emotional states. Once in the blood stream, the alcohol is distributed to all
parts of the body including the lungs, brain and liver. It is the depressant action of alcohol in the
brain that causes impairment and intoxication.
Elimination of alcohol begins immediately after it has entered the blood. Most of the alcohol
(approximately 95%) is eliminated by metabolism in the liver. The remainder (approximately
5%) is excreted unchanged through breath and other body fluids. Unlike absorption, the
elimination process is slow. The elimination rate ranges between 10 ‐ 20 mg% per hour for most
of the population.
The basis for all breath test equipment is that alcohol is eliminated unchanged in the breath.
There is a fixed and known relationship between the amount of alcohol in the breath and the
amount of alcohol in the blood. This relationship (essentially the principle of breath testing) is:
o
At 34 C, 2100 parts of deep lung air contains the same amount of alcohol as one
part of blood.
Using this ratio, it is possible to collect a measured volume of breath, analyze it for alcohol and
convert the result to a blood alcohol concentration. This principle is used in all breath test
instruments and screening devices operated in North America, including the Alco‐Sensor FST®.
It should be noted that this ratio is lower than the actual ratio (2300:1) and so the results
obtained through breath testing tend to underestimate the actual blood alcohol concentration.
2.6 Theory of Fuel Cells
The Alco‐Sensor FST® analyzes the amount of alcohol in a sample of breath by means of a fuel cell.
A fuel cell is similar to a battery except that it requires a fuel (like alcohol) to make it produce a
current. The current is produced by a chemical reaction that occurs when alcohol comes in contact
with the fuel cell:
Alcohol ‐‐‐‐‐‐‐‐‐> Acetic Acid + Electrons ‐‐‐‐‐‐‐‐‐‐‐‐> CO
The current is produced when electrons are generated in the above reaction. The more alcohol
there is in a breath sample, the more electrons are produced causing a stronger current and
subsequently, a higher reading.
Alco‐Sensor FST® Operator's Manual
+ O + H O
2 2 2
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