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An In Depth Look At The Intoxilyzer

There are two Intoxilyzer’s currently being used in the United States. In Texas, the only machine used presently is the Intoxilyzer 5000 model. However, this article will address each Intoxilyzer and attempt to explain how they work and the scientific principles behind them.

The Science

The basic scientific principle upon which the Intoxilyzer 5000 and Intoxilyzer 8000 operate can be found in the Lambert-Beer Law. The Lambert-Beer Law, also referred to as Beer’s Law or Beer-Lambert Law, is the linear relationship between absorbance and concentration of absorbing specific substances. As it relates to alcohol breath testing, when alcohol comes in contact with infrared light, the alcohol absorbs the infrared light. Because this relationship is linear, the higher the concentration of alcohol, the more the light is absorbed. Thus, when exposed to a given amount of infrared light, the concentration in alcohol is proportional to the decrease in light detected by the infrared detector.

Since that explanation is very technical here is an example that might clear things up.

It is like standing at one end of a tunnel and a car, with its headlights on, is at the other end. You can see the car’s headlights without any obstruction, and they appear clear and bright. Add fog to the tunnel, and the fog absorbs some of the light. Now the headlights of the car appear dull and fuzzy. The Intoxilyzer is similar in that it measures the difference in the intensity of the infrared light to get a reading of the amount of alcohol.

The 5000 and 8000 model absorb the alcohol differently because they use different technologies.

Intoxilyzer 5000 Infrared Absorption: Ethanol absorbs infrared light at a high degree of sensitivity at 3.39 and 3.48 microns specifically. Acetone is a substance that can mimic the presence of ethanol absorption because it too absorbs light at a linear measure of 3.39 microns. Ethanol, however, is distinguishable from acetone because while they both absorb infrared light at 3.39 microns, only ethanol absorbs it additionally at 3.48 microns.

Intoxilyzer 8000 Infrared Absorption: The Intoxilyzer 8000 used dual wavelength technology and absorbs infrared light at 3.4 microns and 9.3 microns. The instrument is looking for the specific pattern of ethanol absorption at these two wavelengths. If the specific pattern is not measured, the instrument will detect the compound as an interferent, cancel the test and return to the ready mode.

Now that we have a basic understanding of the science we can move on to explain how the Intoxilyzer 5000 and Intoxilyzer 8000 measure a subject’s breath alcohol level.

Intoxilyzer 5000: At one end of the sample chamber is an infrared light source. This source is a quartz iodide lamp that emits infrared light. The light is directed through a heated sample chamber by a lens. The chamber is heated and maintained at a temperature hot enough to avoid sample condensation. The chamber is sealed so that the sample will not leak, and outside air cannot dilute it. At the opposite end of the sample chamber a second lens focuses the light leaving the chamber through three rotating filters and onto an infrared energy detector. Because the light exiting the chamber still consists of various wavelengths of infrared light, it is filtered so that only wavelengths of 3.39 microns, 3.48 microns, and 3.80 microns are allowed to pass through the filter wheel where it falls on the infrared detector. The detector converts the filtered light into electrical energy. The amount of this energy is directly proportional to the amount of light able to pass through the sample chamber, thus providing a method of measurement.

Intoxilyzer 8000: At one end of the sample chamber is an infrared light source. This light source pulses infrared light into the sample chamber. The sample chamber is heated and maintained at a temperature hot enough to avoid sample condensation. The chamber is sealed so that the sample will not leak, and outside air cannot dilute it. At the opposite end of the sample chamber are two stationary filters (3.4 and 9.3 microns) which filter the infrared light. The filtered light is focused onto an infrared energy detector. Because the light exiting the chamber still consists of various wavelengths of infrared light, it is filtered so that only wavelengths of 3.4 and 9.3 microns are allowed to pass through the filter where it falls on the infrared detector. The detector converts the filtered light into electrical energy. The amount of this energy is directly proportional to the amount of light able to pass through the sample chamber, thus providing a method of measurement.

How it Works

So how is it done? How is a sample taken?

Intoxilyzer 5000 and 8000 – The Intoxilyzer 5000 and 8000 are instruments designed to detect and measure alcohol in a person’s breath by the principles of Infrared Light Absorption. This is how it works:

  • The subject blows into the mouthpiece for at least six seconds (Intoxilyzer 5000) or for a minimum breath volume of 1.1 liters (Intoxilyzer 8000). The instrument emits a steady tone to indicate the defendant is blowing hard enough to provide a sufficient sample.
  • The breath is analyzed in the sample chamber. A beam of infrared light passes through the chamber (Intoxilyzer 5000). A beam of infrared light is pulsed through the sample chamber (Intoxilyzer 8000).
  • The Intoxilyzer (5000 or 8000) measures alcohol in the breath by detecting the decrease of intensity of infrared light passing through the sample chamber.
  • As the concentration of alcohol vapors increases in the chamber, the amount of infrared light reaching the detector decreases.
  • The absorption of this light determines the alcohol concentration, which is read on a digital display and recorded on a print card (Intoxilyzer 5000) or on a report (Intoxilyzer 8000).

Below is more detailed description of obtaining a breath specimen:

  • Intoxilyzer 5000: The subject blows into the mouthpiece, which directs the airflow through the device and does not allow fluid to enter the breath tube. Baffles inside the mouthpiece capture any excessive saliva or moisture. The breath tube is heated to prevent condensation. If condensation were to develop, it could affect the readings. Initially, the instrument establishes a zero reference point by measuring the amount of infrared energy striking the detector when the chamber is filled with ambient air–room air. During a breath test, as the amount of alcohol vapor in the chamber rises, the amount of infrared energy reaching the detector falls. By finding the difference between the zero reference point and the breath test measurement, the instrument determines breath alcohol level. The breath tube also acts as an antenna that may receive radio frequency interference (RFI). An internal hose inside the instrument allows a path for the breath sample to enter a three-way valve. In the open position, the three-way valve allows the breath sample to enter the sample chamber. A pressure switch is attached to the exit end of the sample chamber. As the subject blows into the breath tube, the air pressure activates the pressure switch and a steady tone is heard indicating that the subject is blowing hard enough to provide a sufficient sample. One-way valves inside the tubing ensure that the breath sample cannot be sucked back. Infrared light passes through the chamber to the detector. The degree of absorption of infrared light determines the alcohol concentration, which is digitally displayed and recorded on a print card. The Intoxilyzer 5000 series instrument will detect and compensate for acetone that absorbs infrared light energy in the same frequency range as alcohol.
  • Intoxilyzer 8000: The subject blows into the mouthpiece, which directs the airflow through the device and does not allow fluid to enter the breath tube. Baffles inside the mouthpiece capture any excessive saliva or moisture. The breath tube is heated to prevent condensation. If condensation were to develop, it could affect the readings. During a breath test, as the amount of alcohol vapor in the chamber rises, the amount of infrared energy reaching the detector falls. The instrument can detect radio frequency interference (RFI). The subject blows the breath sample directly into the sample chamber. The instrument automatically senses deep lung air using slope detection, breath volume, breath flow and minimum time. A non-return valve inside the instrument ensures that the breath sample cannot be sucked back. Infrared light passes through the chamber to the detector. The degree of absorption of infrared light determines the alcohol concentration, which is digitally displayed and recorded on a report. The Intoxilyzer 8000 series instrument will detect interfering substances.

Can the Intoxilyzers Make Mistakes

Now, knowing all of that you might ask: are these machines infallible, can they make mistakes? And the answer is most certainly yes. Just to provide a few examples of how this might happen.

The Intoxilyzer is not designed to detect the molecule of ethyl alcohol (ethanol), but rather only a part of that molecule, the methyl group. In other words, it is the methyl group in the ethyl alcohol compound that is absorbing the infrared light, resulting in the eventual blood-alcohol reading. Thus the machine will “detect” any chemical compound and identify it as ethyl alcohol if it contains a methyl group compound within its molecular structure. The Intoxilyzer only assumes that the methyl group is a part of an ethyl alcohol compound.

Industrial compounds such as: paint, glue, gasoline, thinners, and other compounds contain the methyl group which the Intoxilyzer detects as alcohol concentration. No, you don’t have to drink the stuff: simply absorbing it through your skin or inhaling the fumes can result in significant levels of the chemical in your body for hours or even days, depending upon the “half-life” of the compound.

Diabetics with low blood sugar can have high levels of acetone — which is “seen” as alcohol by Breathalyzers. And scientific studies have found that people on diets can have reduced blood-sugar levels, causing acetone hundreds of times higher than found in normal individuals.

If you are a smoker, your Breathalyzer result is likely to be higher than expected. The compound acetaldehyde — reported by the Breathalyzer as “alcohol” — is produced in the human body as a by-product in metabolizing consumed alcohol, and eventually passes into the lungs and breath. Researchers have discovered that levels of acetaldehyde in the lungs can be 30 times higher in smokers than in non-smokers. Result: higher BAC readings on the machine.

On top of false reading from other substances there is always the possibility of a malfunction. The Intoxilyzer machine is fully capable of electrical or mechanical malfunctions, as is any machine. The accuracy of the Intoxilyzer depends, among other things, on the intensity of the light that is beamed through the breath sample; the final reading is determined by the amount of the light that is absorbed by the alcoholic vapor. Thus any reduction in the intensity of the light from the quartz-iodide lamp bulb in the Intoxilyzer will register as the presence of alcohol, and the greater the reduction, the higher the reading. A malfunction in the bulb, then, or a drop in the line voltage (the bulb is designed to perform at 105 to 130 volts) could result in a false reading.

To put this in a list format, the following is non-cumulative list of ways a breath test can be inaccurate:

  • Breath/Blood Partition Ratio: Research suggests that you can have two different people of the same gender, size and weight, who consume the same amount of alcohol, yet their breath alcohol readings can differ by as much as 42%! Only an effective courtroom Dallas DWI attorney can point this out to a jury.
  • Nonspecificity: The machine fails to identify ethanol to the exclusion of all other chemical compounds. In other words, the machine can mistake other compounds for alcohol.
  • Mouth Alcohol: Alcohol in the mouth can result in a falsely high reading.
  • Testing during “absorptive” state: Due to the differing alcohol concentrations in the arterial and venous systems during absorption of alcohol (this can last anywhere between 15 minutes and 2 hours, depending upon your particular circumstances) some leading experts suggest that reliable breath testing cannot occur during the absorptive state.
  • Hematocrit: Different people have a different amount of solids in their blood, such as red blood cells. The machine assumes a certain proportion, but if the person’s is different, the result can be biased and inaccurate.
  • Body Temperature: It is well established that the higher a person’s body and breath temperature, the higher the breath test reading.
  • Breathing Technique: Breathing technique can affect the breath test result by up to 30%.
  • Stress: tress can affect blood pressure and breath test readings.
  • Used Mouthpieces: Regulations require clean mouthpieces for each test. Used mouthpieces could contain residual alcohol.
  • Simulator Calibration: Improper calibration of the reference solution can result in an improper reading.
  • Ambient Air: Rooms where DWI suspects are routinely tested on a breath machine may contain the exhaled breath of those suspects who have been previously tested. The result is that the sample chamber could be purged with alcohol-polluted air.
  • Incomplete Purging: An incomplete purging cycle during the machine’s operation sequence can result in improper readings.
  • Radio Frequency Interference (RFI): Research suggests that RFI can affect the result by up to 40%.
  • Testing after an Auto Collision: This can result in stress and high blood pressure.

The most important thing to remember is that you need a tough, aggressive, and trusted Dallas DWI lawyer if you’ve been arrested for a drunk driving offense. Contact the Law Office of Mark T. Lassiter today for an experienced Dallas DWI attorney.


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