Physiology Of Breath Testing - Intoximeters Alco-Sensor FST Operator's Manual

An ASD demand must be made without any delay. Generally a MAS demand should be made as soon as
stopping a vehicle. For 320.27(1)(b) demands they should be made as soon as an officer forms the
reasonable suspicion of alcohol being present in the suspect's body. The officer should read the ASD
demand exactly as written.
3.0 P
This brief chapter is included to explain how breath samples are used to determine the blood alcohol
concentration.
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. The absorption time
may be affected by the type and amount of food in the stomach and the type of beverage consumed. 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 the alcohol begins immediately after it has entered the blood. Most of the alcohol
(approximately 95%) is eliminated by metabolism in the liver. The remainder (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 instruments 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:
2100 parts of deep lung air contain 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 content. 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.
A -S FST®
LCO ENSOR
HYSIOLOGY OF
Figure 1 Only deep lung air can reflect the true alcohol concentration.
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