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Las Vegas police use the Intoxilyzer 5000EN for evidentiary breath analysis of suspected DUI / DWI drivers. The machine uses infrared light to scan the breath for alcohol (ethanol) and some organic interferents through four filters. The machine is designed to see and quantify only ethanol, but in reality, it can see other volatile organic compounds (VOCs) in a breath sample and is supposed to flag them as "interferents". Some experiments have shown that these VOCs can, under certain conditions, be mistakenly read as ethanol and thus result in a falsely high BAC analysis.
There have been some experiments that have shown that the Intox 5000 is good at specificity, which is seeing and measuring the amount of ethanol that is present in a breath sample when there are no interferents present in the breath. Specificity depends upon the machine code that controls how the machine's IR light source, filters and photo detector (lead selenide) work. However, the machine's accuracy has been questioned because of its apparent inability to differentiate some volatile organic compounds from ethanol when both are present in the breath. The conversion of what the machine detects at the photo detector into a BAC quantification of the breath sample is controlled by the source code. Thus, where the machine's specificity is controlled by the machine code, its accuracy is dependent upon its source code. So far, the manufacturer has largely refused to release the source code for scientific scrutiny and validation. If there are no errors in the code and the machine is accurate under all circumstances, why would the manufacturer be reluctant to prove it?
Finally, a legal source of error in the breath analysis is the statutory partition ratio. DUI law in Las Vegas and other cities in Nevada instructs the machine to use a partition ratio of 2100:1 in its blood-to-breath ratio of ethanol. The problem is that this causes a significant portion of the population to be given a wrongfully high BAC quantification by the breath machine. That is, a blood analysis taken at the same time as the breath test would indicate a substantially lower blood BAC than the breath BAC. The statutory DUI partition ratio has certainly caused many lower BAC drivers to be falsely convicted of DUI in Las Vegas.
All things considered, the breath test is more likely to give a falsely high BAC reading to smaller people (literally people with smaller than average lungs), people with asthma, with COPD (chronic obstructive pulmonary disease), people who work with VOCs (such as furniture finishers, beauticians, mechanics, etc.), poorly controlled diabetics and people on high protein and/or low carbohydrate diets.
Only a True DUI Attorney knows how the breath machine works and how to exploit its shortcomings. Only a True DUI Attorney can effectively challenge the breath machine results at trial.
