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How does a (DUI) breathalyzer work?

Fresno DUI Defense Attorney | Fresno DUI Defense Lawyer

Explaining the breath machine and the errors that can occur

Breath Tests for Alcohol are commonly employed by law enforcement.  There are different types of Breath Testing Machines.  The first type is an IR device that measure the characteristics of the molecular bonds and organic molecules when IR light strikes them.  The second type, most commonly employed in the Fresno area and greater Central Valley is the "Fuel Cell Breath Test" devices. These machines actually consume the organic material in the exhaled breath as fuel.  The energy created by the consumption of the organic molecules (which are not entirely specific to ethanol alcohol, which is the type of alcohol which is consumed by humans in distilled or fermented beverages.

Most common questions involve who accurate a breath machine can be.  This has been answered by experts across the nation many times, despite the truth of the science behind the machines showing they can be extremely inaccurate, lacking of precision, and entirely misused during the period of time between consumption of the alcoholic beverage and equilibrium within the blood in the body, government experts will commonly testify otherwise.

7 Deadly Errors in Breath Alcohol Measurement and Conversion to Blood Alcohol Levels

1.  Machine Error: Every machine has a margin of error.  Accuracy and precision are very important.  Accuracy is more correctly described as a measurement of inaccuracy.  The best description is if a particular gun is fired at a bulls eye numerous times, and all the bullets strike the target within 2 inches of the bullseye, the gun was firing at an accuracy level of or level of inaccuracy of 2 inches or less.  Precision describes the how precise each shot was in relation to the other shots.  For example, if a a target has been fired at four times, and each missed by exactly 2 inches, it would be accurate to within two inches.  One shot was high two inches.  The next shot was low two inches.  The next shot missed to the right by two inches.  The last shot was two inches to the left.  The results show a level of accuracy of two inches, but a horrible level of precision.  If, all four shots missed by two inches, but each hit precisely the same spot, resulting in a single hole in the target, it would be extremely precise.  Breach machines have not shown this level of accuracy or precision.  In fact, we commonly see breath tests that are extremely inaccurate and exhibit a low level of precision.

2.  Breathing Pattern Error: The machine consumes the organic chemicals in the exhaled breath, assumes they are alcohol, then estimates blood level based on a pres set program.  However, one error that is inherent to the machines is assuming it was properly used by the operator.  This means having the subject exhale at the proper time.  If a person is hyperventilated or holds their breath, the results are affected.  Simply holding ones breath for 20 seconds causes an increase in the breath alcohol concentration estimate of 15% over the true value. An officer may simply instruct a subject to inhale, and pause before inserting the device into their mouth, causing an inaccurately high estimate of the subjects blood alcohol concentration.   This is due to the continuous exchange of gases that takes place within the lungs during this time.

3.  Exhaled Breath Temperature/Core body temperature: The Breath Machines used in California are programmed to assume, usually incorrectly, that the subjects breath temperature is 34 Degrees Celsius.  Fact is people vary greatly in their core body temperature and likewise in the temperature of their exhaled breath.  The study the software was based upon was very small, conducted in 1950, and involved only 6 subjects.  A more recent study conducted in 1996 involved 700 subjects, and recorded a range from 33-36.7 Degrees for exhaled breath temperature. The study concluded that for each degree increase in deep-core body temperature the Breath Alcohol Concentration's estimate of the Blood Alcohol Concentration increased 8.6%.

4.  Hematocrit Error: Hematocrit is the solid matter within the blood.  Red Blood cells are the predominant source of hematocrit in blood.  The more hematocrit, the less water, within which the alcohol dilutes.  The higher the the hematocrit, the more solids in the blood, less water, and higher estimated BAC.  Lower Hematocrit, has less solids, more water, and a lower BAC result.

5.  Partition Ration Error: All Breath machines use a partition ration, in the United States the ratio is deemed to be a 2100:1.  That means that amount of alcohol in an exhaled breath is multiplied by 2100, to estimate the blood alcohol content.  Studies have found, like most every other aspect of humans, we are unique and exhibit different true partition ratios.   Partition rations vary depending on many factors between true partition rations of 900:1 up to 3400:1.  One of the factors to be aware of is that a breath machine is seriously at risk of overestimating BAC during the absorption phase.

6.  Mouth alcohol Error:  Even machines with a "slope detector" do not adequately distinguish between breath alcohol and mouth alcohol.  The air flowing over the liquids, saliva, mucous, and possible mouth alcohol can pick up additional alcohol molecules that will greatly influence the machine.  This additional alcohol content is then combined with the breath alcohol and cause the machine to inaccurate estimate blood alcohol content.

7.  Extrapolation Error: The machine takes a very small sample, then extrapolates the amount of alcohol to the equivalent of the amount that would be present in 210 Liters of air.  The machine captures and measures about a cubic centimeter.  The sample is about the size of a dice.  210 liters is about the size of 2 27.5 gallon trash cans.

With all of these potential errors, that can not be eliminated or safeguarded against, how can we trust the results?

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