Written by attorney David Nelson Jolly

The DUI Guide: DUI Evidentiary Breath Test Devices (Breathalyzer)

Published with permission from the book, DUI/DWI: The History of Driving Under the Influence, David N. Jolly. Outskirts Press (2009)

The DUI Guide: DUI Evidentiary Breath Test Devices


In 1954 Dr. R. F. Borkenstein invented the the Breathalyzer. The invention of the breathalyzer provided law enforcement with a non-invasive test providing immediate results to determine an individual's BAC at the time of testing. The Breathalyzer machine measures the percent weight by volume of blood alcohol using photometric measurement of a quantity of alcohol and a measured sample of deep lung (alveolar air). The Breathalyzers were manufactured by Smith & Wesson in Springfield, Massachusetts until July, 1984, until the Breathalyzer division was sold to National Draeger, Inc., an American subsidiary of a German manufacturing company.

Like all photometers the Breathalyzer Model 900 worked by using a measured quantity of alveolar that is then bubbled through a solution contained in a glass jar called a test ampoule. The solution is a mix of potassium dichromate and sulphuric acid in water which acts with a catalyst known as silver nitrate. When the alcohol mixes with the solution, it becomes oxidized to acetic acid. The potassium dichromate is then reduced in proportion to the quantity of alcohol that is oxidized and this reduction results in a loss of color to the solution. This loss of color allows more light from a source on one side of the ampoule to pass through onto a surface on the other side. The resulting amount of light that passes through is proportional to the amount of color change and the amount of alcohol present.

During the test two ampoules are used and each ampoule is chemically identical. Within the unit there is a lamp that is located on a movable carriage between the ampoules. The lamp directs light through each ampoule and onto a distant surface. This carriage is then adjusted so that the light on the two surfaces is identical. The second ampoule however, is considered a “reference ampoule" and is never exposed to any chemicals and as a result, never changes color. Once the test ampoule is exposed to the breath sample and reacts, the amount of light that passes through the two ampoules is compared a second time. The difference is then measured and converted to a measurement of blood alcohol concentration. That figure is then multiplied by the 2100 to 1 ratio to give the blood alcohol concentration.

The potential number of sources of errors in the Breathalyzer are many. For instance, the reagent which detects ethyl alcohol will also react with any other reducing agent that it comes into contact with. This is a concern since there are a number of interfering substances which can potentially affect the reagent, including acetone, methanol, acetaldehyde, among others, none of which are “alcohol." Additionally, if the ampoule is broken it is possible that anything adjacent (ie. foreign substances on the operator’s clothing or body) may make their way into the ampoule, thereby affecting the test. Further, things such as smoke, paint, or any other foreign substance can also be transferred from the bubbler tube into the reagent.

Another issue with the Breathalyzer is acquiring a breath sample of sufficient concentration. If the sample is not of sufficent concentration it could lead to innaccurate readings. Further, the temperature of the chamber may also result in readings that are either too high (when the chamber is too cool) or too low (when the chamber is too hot).

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