Facing painful accusations of drunk driving, Dale Lee
Underdahl of Minnesota challenged the accuracy of the Intoxilyzer 5000EN
breathalyzer used against him, and demanded to see the source code used in the
The claim launched debates and a lawsuit that escalated all
the way to the Minnesota Supreme Court. The device’s manufacturer, CMI, Inc. of
Kentucky,claimed the source code was proprietary, copyrighted and refused
to comply. To that end, CMI attempted to
block the source code’s release by filing a writ of prohibition, which was
denied by the Minnesota Supreme Court, who said the writ is “an extraordinary
remedy and is only used in extraordinary cases.”
The State of Minnesota specifically commissioned the Intoxilyzer 5000EN model and “all right, title, and interest in all copyrightable material” created “will be the property of the state,” according to the state’s original bid proposal. Furthermore, the proposal also said CMI must provide
the necessary information to “attorneys representing individuals charged with
crimes in which a test with the proposed instrument is part of the evidence,”
to CNet, “seems to include source
On July 26, the Minnesota Supreme Court ruled in Underdahl’s favor,
assuring the discoverability of the devices source code and affirming his right
to its examination. “The problem is, the manufacturer of the thing thinks they
can hold it back and not tell anybody how it works. For all we know, it's a
random number generator,” said Underdahl’s attorney, Jeffrey Sheridan.
The Minnesota Department of Public Safety has expressed
reluctance to forcibly acquire the source code, and according to a department spokesman,
is still considering its response. The department thinks a lawsuit is
unnecessary as the contract stipulates CMI’s cooperation with court orders.
The “source code defense” has been used in a number of other
states with mixed success. Manufacturers, in the interest of guarding their
trade secrets, have rigorously fought against court-ordered scrutiny. In one instance,
judges in Florida’s Seminole County threw
out hundreds of cases involving breath tests because the manufacturer would
not disclose their breathalyzer's source code. However, in another instance a
group of more than 150 suspects, in Florida’s Sarasota County, were
granted access to the machines’ source code, with the judges citing it
was “material to their theory of defense in [their] cases.”
quote: Body Temperature: The widely used blood-to-air partition ratio of 2100 is based on a normal body temperature of 98.6°F. A higher body temperature of the individual will overestimate the actual BAC because of the higher volatility (or vapor pressure) of liquids like alcohol at a higher temperature. An elevation in body temperature of 1°C (1.8°F) results in a 7% higher value in the result since the air in the lungs will contain an artificially higher amount of evaporated alcohol. Therefore, a person with a body temperature of 100.4°F, and with an actual blood alcohol of 0.0935%, will register a value of 0.10% by the breath test. Be careful if you have a cold or the flu.
quote: Cellular Composition Of Blood: Blood contains suspended cells (e.g. red and white cells) and proteins, and is therefore only a partial liquid. The partition ratio of 2100 is based on an average cell volume 47%. Some of this cell volume is tissue, and at 47% cell volume, 81.5% of the blood volume is liquid in which the alcohol is actually dissolved. A person with a lower cell volume will have a falsely elevated blood alcohol level based on a breath test since the amount of alcohol in 2100ml of lung breath will be dissolved in a slightly higher amount of liquid, and hence have a lower concentration. Cell volume values range from 42% to 52% in males, and 37% to 47% in females. This variability will only have a small impact on BAC (ranging from -2% to +5%) so don't rely on it in court.
quote: The ratio of breath alcohol to blood alcohol is 2100 to 1 (and called the partition ratio), so the alcohol content of 2100 milliliters of exhaled air will be the same as for 1 milliliter of blood. The maths are simple from there and leads to blood alcohol readings expressed as a percentage of alcohol in the blood.The partition ratio can vary between 1700 and 2400 depending upon the individual and local environmental conditions, leading to a breath analysis reporting either a higher or lower calculated blood alchol reading.