Breath Testing

Breath testing is one way that the police determine if a person is driving under the influence in Greenwich and throughout the state of Connecticut. But what are breath tests? How accurate are they? Why are they used in Connecticut? We answer all of these questions and more on this page. For help defending against a DUI charge, contact us.


In Greenwich, breath testing machines are a common tool used by law enforcement to test for the presence of alcohol on the breath after a DUI arrest. When a police officer uses a breathalyzer device, they will instruct the arrestee to take a breath and then exhale air into the device through a small mouthpiece. The air goes into the device, and as it travels into the device, the air passes through a light source, similar to a bulb. You can learn more about Greenwich breath testing on this page.

Breath Testing Science

This breath analysis is based on scientific law called Henry’s Law. This law is defined as the “mass of 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.” This means that if a liquid and a gas are confined in a closed container, the concentration of the gas in the air above the liquid is proportional to the gas that is dissolved in the liquid.

This can best be thought of as a situation 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 Henry’s constant. The ratio given to that of the blood in the human body to be used in accordance with this law is 2100:1. The concentration of alcohol in the average person’s blood is approximately 2100 times as great as the concentration in the air with it.

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Issues With Breath Testing Devices

The problem with this is that there is no normal amount of blood/air constant because every person’s body weight, frame, and physical makeup is unique. Scientists have determined that there can be up to a 0.03% error or more with each breathalyzer due to the normal ratio being used as a constant in the breathalyzer. This can mean the difference between a DUI charge and walking away from a police stop.

Other factors can influence breath test results. For example, a person’s body temperature can also impact the results because an increased or decreased body temperature can increase the percentage of the blood alcohol concentration due to the volatility of alcohol. Taking a heavy dose of aspirin can even cause the body temperature to be reduced and potentially alter the breathalyzer results. Medical problems such as diabetes, sickness, and medication can all be possible defenses to the breathalyzer results.

Another factor that can seriously alter the accuracy of a breathalyzer is poor maintenance or improper calibration of the breathalyzer device. Improper calibration of the device makes the test unreliable and can cause the entire test to be thrown out as evidence. In order for the test results to be admissible in a court case, there are general guidelines that law enforcement must follow when it comes to their breathalyzer devices.

The breathalyzer must be properly maintained and checked for accuracy at consistent intervals, and the person administering the breath test must be certified to use the device and administer the device in accordance with breathalyzer training. The officer administering the test must also inquire about factors that could alter the sample result such as eating or burping before the test was administered. The breath testing must also be able to capture at least two measurements that are within .02 of each other to be considered accurate or reliable results.

Under Connecticut law, each person who gets behind the wheel and drives on the road has implicitly consented to a breath test that tests blood alcohol concentration. However, just as you may decline to take field sobriety tests and answer questions, you may also decline to take the breath test, as the police legally cannot force you to take it. However, there are consequences if you don’t take the test, such as automatic license suspension, though the consequences of taking the test and having that evidence used against you in a criminal case may be far greater.

A good Greenwich DUI defense attorney will be able to analyze a DUI case where there are breathalyzer results or a breathalyzer refusal and advise you on what defenses you may have. If you have been arrested for a DUI in Greenwich, call Lady DUI to find out more.

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