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Breathing into a breathalyzer can feel like testifying against oneself; technology cannot lie, there is no arguing against it, or so police officers, prosecutors and their expert witnesses would have you believe.

But is that really the case? Are breathalyzer tests infallible

Part of establishing reasonable doubt in defending against drunk driving charges is challenging the technology that prosecutors use as evidence. Understanding how breathalyzer tests work is the foundation for finding ways that they may have given inaccurate results. 

There are multiple factors that can influence the accuracy of a breathalyzer’s readings. This post covers a few examples.

Does the concentration of alveolar air in a breath sample make a difference? At least one study suggests that alcohol exchanges from the bloodstream to the lungs in the upper airway. This may affect the result of a test, depending on the lung volume of the person providing a breathalyzer sample, because people with larger volume may provide a sample with less alveolar air, which may produce a lower alcohol concentration.

Do breathing patterns have an influence on breathalyzer results? Some breathing behaviors may increase alcohol concentration in the test sample, such as holding one's breath, or keeping one's mouth closed for five minutes beforehand, both of which may increase the concentration. Even heartburn (gastric reflux) or belching may have an effect; the presence of residual alcohol in the mouth, or even small amounts of stomach contents or gas can create an artificially high reading.

Can substances other than alcohol affect the test result? Evidence suggests that exposure to some chemicals, such as paint thinner or lacquer, can trigger a breathalyzer test reading in the same way that alcohol does. Even the fuel cell used in some test devices can read substances other than ethanol alcohol, but may not be able to distinguish these from ethanol.

Can quality control problems affect the quality of the test sample? Instances have occurred demonstrating that the lack of quality assurance and quality control procedures, and even outright falsification in the police laboratory environment can lead to compromise of test results.

These examples are but a few of the ways in which breathalyzer tests, instead of being technologically infallible, can in fact lead to questionable if not erroneous results. It is among the roles of your defense attorney to diligently explore all relevant possibilities through which reasonable doubt may arise at trial.

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