A Brief Overview of how a Breath Test
Ohio's main breath testing machine is the BAC DataMaster.
The two other primary machines are the Intoxilyzer 5000 and
the BAC Verifier (which is not manufactured any longer).
These machines use a principle called infrared analysis.
In a nutshell, alcohol absorbs
infrared energy at a certain frequency when an infrared beam
is sent through the breath containing alcohol. The breath is
held by a sample chamber inside the machine. The beam is
emitted from the infrared source, also located within the
machine. The more alcohol present in the sample chamber
(known as an alcohol concentration) the more infrared light
is absorbed. The amount of infrared energy absorbed by the
breath sample in the sample chamber is calculated by the
machine's internal computer to calculate and print out a
breath alcohol reading (known as a BAC evidence ticket).
There are a number of problems with
this type of "science". Many people have heard that you
should not take a breath test if under arrest. Have you ever
wondered why? Keep reading. . . .Determination of BAC by use
of a breath test, is by far the most popular scientific test
for drunk driving. The breath test involves the measurement
of alcohol in an appropriate sample of breath, expired
alveolar air. (Alveolar air is that part of the expired air,
which is in equilibrium with blood-the bottom of the lungs).
The breath test machine then converts
the breath sample into a corresponding blood equivalent.
Unfortunately, this conversion ration assumes that all human
beings are of the same height, weight, body temperature,
etc., etc. The commonly used partition-ratio of 2100 can be
expressed as follows:
In principle, this ratio is determined by simultaneously (or
as close to simultaneous as experimentally possible)
measuring the concentration of alcohol in the blood and
expired alveolar air of test subjects administered alcohol
under controlled conditions. While values in the scientific
literature for this ratio range from 1900 to 2400, an
international panel chose, in 1972 Essentially by fiat, the
currently accepted value of 2100. Brent, supra at 133.
Some factors that affect the partition-ratio, such as the
effect of temperature, may be obvious, even to a
non-scientist. There are others that are not so apparent.
These factors can either increase or decrease the actual BAC.
The most common problems with breath
testing in Ohio center around irregular calibration checks,
the presence of mouth alcohol in the motorist who is
submitting a breath sample, smaller motorists who cannot
muster enough breath volume to activate the machine, police
radio interference (RFI), and machines that have sketchy
maintenance and repair histories.