DUI Defender

How Roadside Breath Machines Work

Roadside breath test devices typically use an electro-chemical reaction to measure breath alcohol content. Air, from a suspect or calibration machine, is blown over a porous disc. This disc is a wafer of materials, one of which will react with the alcohol, freeing electrons and causing a small electrical current. This current is measured and then translated in to an alleged Breath alcohol content.

In order to ensure a “good” breath sample, the devices measure the flow time of the air sample and “capture” a sample near the end of the “average” persons breath. Some devices are also equipped to allow a “manual” capture by the officer if the flow rate and time is not met. This is done by the simple pushing of a button.

Typically in breath testing, not all of a person’s breath is tested, only a small portion is reviewed. This is done by a simple piston popping closed once blow time or manual trapping has occurred. This sample is then analyzed and the results displayed.

Problems with Roadside Breath Machines
Because these devices only sample the air stream, they can easily end of measuring mouth alcohol instead of true breath (also known as deep lung alcohol). Laboratory machines typically have a “slope detector” that allows a trained operator to distinguish between the two. With a slope detector there is constant monitoring of the breath as it passes through the sample chamber and an evaluation made. Any rapid falling off of the alcohol level, or “slope”, triggers the sensor to indicate mouth alcohol.

Next, these machines are subject to more calibration problems. Unlike their big brothers, these machines are not being kept and maintained by laboratories and their staff. Most are housed by local cops or CHP. The maintenance, or more appropriately, calibration is being done by police officers with no scientific back ground.

Depending on the underlying technology, some roadside breath analyzers might be subject to other serious problems. For example, with fuel cell devices there is a lack of specificity: the devices will detect a large number of chemical compounds, indiscriminately “reading” them as ethanol. Although the manufacturers of the passive alcohol sensor claim in their advertisements that it “is unaffected by acetone, paint and glue fumes, foods, confectionery, methane and practically any other substance likely to be found in the breath,” the fact remains that any device using fuel cell oxidation is not specific for ethanol; the manufacturer’s use of the term “practically” should certainly create suspicion.

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