When is a Breathalyzer not a Breathalyzer?

Although it has become a common term to mean breath alcohol tester, technically, Breathalyzer is a trade name for particular piece of equipment, which is used for determining a person's blood alcohol concentration (BAC). There are two other kinds of devices that are commonly used to measure BAC: Alcosensor and Intoxilyzer.  Each uses a different method for measurement than the Breathalyzer.

All three devices are similar in that they require a person to exhale into them but different in the way they measure the percentage of alcohol. That is because each test is based on the same principal, which is that alcohol appears in the breath because it goes almost directly into the bloodstream - not digested - where its chemical make-up remains unchanged.

As a person's blood pumps through his or her lungs, any alcohol present, because it's volatile, evaporates into their lungs. There is a direct relationship between the percentage of alcohol in a person's lungs and the percentage of alcohol in their blood.  This can be tested to accurately determine how much alcohol is in the blood without having to draw any.

All blood alcohol testing devices measure alcohol in the breath and use this relationship to calculate how much alcohol is present in a person's blood. All the devices have a mouthpiece through which a person blows air and a chamber to hold the air sample, but the similarities end there.

The Breathalyzer measures alcohol percentage by examining a change of color generated by a chemical reaction. In addition to the sample chamber and mouthpiece, the device has two glass vials for containing the chemical reaction and an arrangement of photocells coupled to a meter. The air sample is passed through one vial containing chemicals and then into another vial. From that vessel, the lung air sample is blown over the photocells so the gauge can assess the color change and calculate the blood alcohol content.

Rather than detecting color change, Alcosensor performs its task by sensing the amount of a chemical reaction of alcohol in a fuel cell. The fuel cell has two platinum electrodes with a porous acid-electrolyte material layered between them. As the person’s exhaled air blows past the electrodes, the platinum oxidizes any alcohol in the air and produces acetic acid, protons and electrons. The electrons then flow through a wire that connects the first electrode, an electrical-current meter and a another electrode, which then converts the other constituent parts into water. The more alcohol oxidized, the greater the electrical current. A computer chip measures the electrical current and calculates the blood alcohol concentration.

The Intoxilyzer, on the other hand, measures alcohol through infrared spectroscopy, which identifies molecules by the way they absorb light. Different molecules absorb light differently, so alcohol molecules can be recognized, counted and fed into the formula by computer. With the Intoxilyzer, an infrared lamp generates a multiple wavelength beam. This beam goes through the sample chamber and a lens focuses it onto a rotating filter wheel. The wheel uses band filters for the specific wavelength of alcohol. The light that passes through the filters is detected by a photocell, where it is converted to an electronic pulse. Each pulse is transmitted to a small computer which uses these pulses to calculate the blood alcohol concentration.

Each one of these tools is a sophisticated piece of testing equipment that must be calibrated before each use. Police officers must be trained on their proper use and calibration, and attorneys who defend DUI cases often get the results of the tests thrown out of court because of improper use or calibration.

Learn more about the Breathalyzer