It may be easy for most people in Mount Pleasant to assume that if they have been arrested and charged with driving under the influence of alcohol that their conviction is assured if law enforcement has the results of a roadside breath test to use against them. However, that may not be entirely correct. While handheld breath testing devices are the assumed symbol of DUI offenses, their accuracy is often disputed. Indeed, according to research results shared by the National Motorists Association, such devices may have a margin of error as high as 50%.

Understanding how these devices could have such issues with accuracy requires a fundamental knowledge of how they work. Handheld breath testing devices measure the amount of ethanol in a sample. As has been detailed on this blog in the past, gaseous ethanol is expelled in one’s breath shortly after consuming alcohol. Per the Alcohol Pharmacology Education Partnership, breath testing devices determine one’s blood-alcohol content by making two assumptions. The first is that the ethanol concentration on one’s breath is directly proportional to that which is in their blood. The second is that amount is in equilibrium. This equilibrium is represented by the assumed ratio of 2100:1 (1 unit of blood having an ethanol concentration 2100 times greater than 1 unit of breath).

The trouble with that assumption is that a person’s actual blood-to-breath ratio can vary between 1500:1 and 3000:1. How one metabolizes alcohol in their body depends on factors such as age, sex or genetic makeup. Conditions such as how much food is in their system and how long it has been since the person drank also come into play. Each of these elements might be used to challenge the result of a breath test.