Intoxilyzer or Breathalyzer Testing

Manufactured by CMI Inc. of Owensboro, KY, the Intoxilyzer 5000 is a infrared spectrometry breath alcohol measurement tool used by law enforcement to determine the Blood Alcohol Level (BAL) of individuals suspected of Driving While Intoxicated (DWI). The Intoxilyzer 5000 works by measuring alcohol content in the breath in parts per million. Under a theory known as Henry’s Law, the Intoxilyzer 5000 assumes a breath to blood ratio of 2,100 parts breath to 1 part blood. Therefore, by measuring the alcohol content in the breath, the Intoxilyzer 5000 extrapolates the estimated Blood Alcohol Content (BAC).


While many states rely on the Intoxilyzer 5000, they are by no means infallible or completely accurate. In fact, in November of 2005, a Florida court ruling disallowed use of the device when the manufacturer, CMI Inc., refused to give defense attorneys exact information and details about how the device computes Breath Alcohol Content.


In addition, scientific studies have been conducted which uncovered very troubling information about the accuracy of the Intoxilyzer 5000 or Breath Test device. In a study entitled “Variables Affecting Accuracy Precision of Breath Alcohol Instruments including Intoxilyzer 5000” (Rose & Furton) , a medical doctor and professor specializing in Medical Forensics at Florida International University revealed several serious factors which can cause Intoxilyzer 5000 to give incorrect readings.


Looking at the Accuracy of the Breath Test Machine

First, the scientists attacked the theory of Henry’s Law and the 2100:1 ratio by stating “In order to understand the application of this Law, one needs to imagine a capped bottle containing water and a little ethanol. The bottle will contain the water and ethanol in two forms; liquid, and gas above the liquid. This law states that at equilibrium, one can measure the concentration of the ethanol in the gas phase, and from that measurement predict the concentration in the simultaneous liquid phase. The comparison being made is that the lungs are like the bottle, the blood in the lungs is like the liquid in the bottle, and the breath is like the gas phase above the liquid. Unfortunately, Henry’s Law does not apply in the lungs.”

The study further indicates that since the exact conditions required to accurately create Henry’s Law do not exist in the Intoxilyzer 5000, the ratio that is used to calculate intoxication (2100:1) is highly susceptible to false positives (indications that the subject’s Blood Alcohol Level is substantially higher than it actually is).

The same study found that are many additional factors can only further increase the propensity for error, including:

– Individual rate of metabolism of ethanol (alcohol),

– Breathing patterns

– Body and breath temperature

– The presence of other compounds cannot be accounted for by the Intoxilyzer 5000

Additional factors that must be considered are:

– The size of the sample chamber, which is considerably smaller than that of the human lungs

– The sample chamber is never cleaned and only replaced once a year

– The machine is a self-testing machine and the self-testing feature is not independently tested

– The manufacture does not warranty the Intoxilyzer 5000 for accurate and reliable breath testing

– The machine has an acceptable error rate of .02%,

– Any test results will be from the time of testing and not from the actual time of driving.

While the Intoxilyzer 5000 may be the “Gold Standard” for law enforcement, it is by no means absolute or incontrovertible evidence that a subject was intoxicated.



Stefan Rose, M.D. and Kenneth G. Furton, Ph.D. “Variables Affecting Accuracy Precision of Breath Alcohol Instruments including Intoxilyzer 5000” July 7, 2003, (pg. 1-12).



– It is your right to refuse the Field Sobriety Tests

– It is your right to refuse the Breath Test and/or Blood Test


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