What to Know About the Breath Testing Device for CT DUI

Breath testing devices, also known as "breathalyzers," can be utilized by the police if they think that a person is driving under the influence. You can learn more about breath testing devices, the science behind them, and defenses to breath test results on this page. For more assistance, contact us.


In the state of Connecticut, a breath testing device is used by law enforcement. These devices are used to test for the presence of alcohol after a driver has been arrested for DUI. These machines use infrared spectroscopy. This identifies molecules based on the way they absorb infrared light. Scientists discovered in the 20thcentury that all molecules are constantly vibrating. These vibrations change when the molecules absorb infrared light. The changes in vibration includes the bending and stretching of various bonds.

Each type of bond within a molecule absorbs infrared light at different wavelengths. To identify ethanol in a sample, a scientist has to look at the wavelengths of the bonds in ethanol. They have to measure the absorption of infrared light. The absorption wavelengths help to identify the substance as ethanol. The amount of infrared absorption indicates how much ethanol is present.

Breath Testing Device

The breath testing device has a cell where the driver exhales air. There is an inlet for the cell and there is an exhaust portion of the cell. There is also a sample chamber where the breath travels. The light source is similar to a regular light bulb that produces energy. It is the same type of energy that an electric stove emits and that one can feel when the burner turns red.

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The breath testing device has a wheel at the outlet of the chamber. This is where the light goes through. There are five different filters. The filters act similar to sunglasses. Each filter is different. They filter out all unwanted light. This allows only small portions of light to come through. As the wheel goes around, small pulses of energy occur impacting the receptor as the filters break it up. The amount of heat that is sensed goes through what is referred to scientifically as an “A to D” (analog to digital) convert.

The computer system inside doesn’t automatically recognize that type of signal. It has to be converted to a digital signal first. It is then sent to a computer where it is reduced to numerical values. That numerical value is then shown on a small screen on the face of the device. Then, it prints out a readable result for the police. You should have a copy of the report. If the machine used is a Draeger Alcotest 9510 machine, the breath testing device results will be listed under the column “breath analysis” under the row subject “IR”.

Henry’s Law

Breath analysis is based on the scientific law known as “Henry’s law.” Henry’s law is officially defined as, “the mass of a gas that dissolves in a definite volume of liquid which is directly proportional to the pressure of the gas provided that the gas doesn’t react with the solvent.” In everyday language, this means that if a gas and liquid are in a closed container, the concentration of the gas in the air above the liquid is proportional to the concentration of the gas that is dissolved in the liquid. This can best be related to a thought experiment in which blood is in a closed container that contains alcohol.

The alcohol will evaporate until the concentration in the air above the liquid is equal to that in the liquid. This is known as a fixed constant or “Henry’s constant.” The ratio given to that of the blood in the human body to be used in accordance with Henry’s Law is 2100:1. This can best be explained as the concentration of alcohol in an average person’s blood. This is approximately 2100 times as great as the concentration in the air with it.

Impact of Henry’s Law

What this means is that if the alcohol concentration found in blood is in equilibrium with the alcohol in air, the alcohol concentration in the blood should be close to 2100 times greater. The problem is that there cannot be a normal status for the blood/air equilibrium because not every person has the same body weight, frame, and physical makeup. The ratio would be much wider depending upon the person being tested because the human body is not an ideal subject for a sealed container. Forensic scientists determined this problem of the “normal” ratio. There can be up to 0.03% error or more with a breath machine due to the normal ratio being used as a constant with the breath machine.

Temperature Impact

In addition to the issues of the ratio of the breath machine, the temperature of the individual supplying the sample can impact the reported results. What this means is that the temperature of the person taking the test could affect the results. A temperature increase of only two degrees Fahrenheit will cause about a 10 percent increase in BAC results due to the volatility of alcohol. Likewise, a drop in temperature can cause similar results. Also, a heavy dose of aspirin can cause body temperature to be reduced and thus potentially alter the results.

These two issues of breath can be used as a viable defense when being charged with a DUI. If you have taken any medication or have been sick, it is a good idea to tell the officer when they question you, or to later tell your attorney. Let your attorney know about any medical conditions that could affect your normal blood ratio. They can obtain the correct medical documents to support your claims. If you are a diabetic, the police officer and your attorney should know because a diabetic can naturally produce ketones, which can skew the results of the breath test. A dedicated DUI attorney like myself can review your medical history and investigate any possible medical defenses to the charges brought against you.

Do you have questions about breath testing devices? If so, you can contact my office. I am happy to answer any of your questions.

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