Police officers and prosecuting attorneys would like for everyone to believe in the infallibility and reliability of breathalyzer machines. If breath test machines were truly 100% accurate, convicting or exonerating suspected DWI offenders would be fairly easy; simply compare an individual's readings to the accepted legal limit.
But despite the claims of prosecutors and policemen, the same science used to design the breathalyzer also shows that any number of biological factors can cause erroneous readings. If you are arrested for DWI, an adverse breath test result is not the end of the line.
The "Partition Ratio"
The "partition ratio" is a comparison of the alcohol in blood and the corresponding amount of alcohol carried on the breath. Most breathalyzers operate using a 2100 to 1 partition ratio; i.e., the assumption that there is 2100 times as much alcohol in one milliliter (ml) of a person's blood as there is in one ml of the same person's breath.
However, studies show that, while the majority of the population may have partition ratios close to the 2100 to 1 ratio assumed by breathalyzers, this ratio is not constant, and fluctuates even within the same individual over time. Furthermore, documented partition ratios in normal human beings range from 1300:1 to 3100:1, meaning that there could be significant disparities between an individual's results and his/her actual blood alcohol content.
Hematocrit and Breathalyzer Error
A person's hematocrit (HCT) is a measurement of how much of his/her blood volume is composed of red blood cells. Because red blood cells are the oxygen-carrying cells in the blood, they affect the rate at which blood alcohol leaks into the air through alveoli in the lungs.
Though some breath test machines are calibrated for an average 46% hematocrit, such a number is not representative of the natural variations found across the population. In fact, the spread of possible hematocrit percentages is usually considered to be as large as 10%. A person with a hematocrit at the lower end of this range would receive falsely elevated test results.
The Result?
Some studies have shown that, in calculating an individual's true blood alcohol concentration (BAC), breathalyzers can be 'off the mark' by as much as 15%. Furthermore, nearly 1 in 4 people receive breath test results higher than their actual BAC - hardly meeting the standard of "beyond a reasonable doubt."
For more information, visit the website of Austin DWI attorneys Morales & Navarrete at http://www.dwi-lawyers-austin.com.
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