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Reviewing the margin of error in breathalyzer devices

Those facing drunk driving charges in Roanoke may think that there options for challenging the charges against them are limited if authorities are using the results of a breathalyzer test against them. The common school of thought is that such results offer scientific proof of one’s intoxication, yet that may not necessarily be true. As is the case with almost every measuring device, there is a degree of error that should be taken into account when dealing with breathalyzer devices. Knowing what that may be requires that one also understand how a breathalyzer test generates a measurement. 

Breathalyzers measure the ethanol content in a breath sample, and then uses a conversion factor in order to draw a conclusion about the ethanol content of the blood of the person from whom the breath sample came. According to the Alcohol Pharmacology Education Partnership, two points are assumed when making this conclusion. First, it is assumed that the sample follows the parameters of Henry’s Law, which is that the concentration of gas in a liquid is directly proportional to the concentration of the same gas in the air directly above that liquid. This equates to (in the context a breath test) the concentration of ethanol in one’s breath being proportional to the concentration of ethanol in their blood. 

The second assumption is that the air one exhales is in equilibrium with their blood. For the purposes of a breath test, the equilibrium ratio that is assumed is 2100:1 (one milliliter of blood having 2100 times more ethanol than one milliliter of breath). In reality the blood-breath ratio  of individuals ranges between 1500:1 to 3000:1. This wide range may contribute to the wide margin of error present in breathalyzer devices, which (per the National Motorists Association) can be as high as 50 percent.