Intoxilyzer Breath Test in OUI, DUI: How it Works, What it Means

An Intoxilyzer 5000 or 8000 Breath Alcohol Test is key evidence in many Maine OUI or Operating Under the Influence cases. A person is guilty of OUI in Maine if they drive with a breath alcohol concentration at or above .08 grams per 210 liters of breath. People who are charged with Operating Under the Influence will usually get a copy of the breath test either from the police, the Bureau of Motor Vehicles, or the District Attorney’s Office. While the form shows a result at the bottom, it doesn’t say anything about how the machine works or how to read the print out. Here I will discuss what the Intoxilyzer machine does, the internal calibration and testing process, and I will take you through an annotated test result sheet to explain what each entry on that form actually means.

How the Intoxilyzer Works

The Intoxilyzer 5000 and the newer 8000 machines work by exposing air in a sample chamber to infrared light. An emitter produces a known amount of infrared light which passes through the sample chamber to reach a sensor at the opposite end. Alcohol molecules are known to absorb a certain amount of infrared radiation and so, if alcohol is in the sample chamber, a predictable proportion of the light will not reach the sensor. The machine compares the light sent with the light received in order to calculate an alcohol concentration. The more infrared radiation is absorbed, the more alcohol is in the breath sample.

OUI by Blood Alcohol or Breath Alcohol Concentration

The Intoxilyzer was developed to use the breath as a way to measure a person’s blood alcohol level. This makes sense since alcohol in the breath is not intoxicating, it’s alcohol in the blood stream that impairs a person’s ability to drive. For this reason, the intoxilyzer is designed to measure breath not from the throat or mouth, but from the lungs. The lungs function to exchange gases in the blood with gasses in the atmosphere. As we breath, some alcohol will vaporize into the lung air to be expelled in the breath. Measuring this lung air is then an indirect way of measuring how much alcohol a person absorbed into their blood.

According to generally accepted science, the lungs exchange blood alcohol with air at a rate of 2100:1. Put another way, for every 2,100 molecules of alcohol in the blood, 1 molecule will escape into lung air. By measuring the breath alcohol and then using the 2100:1 ratio, the machine calculates what the blood alcohol level could have been. That means that the Intoxilyzer measures blood alcohol content by looking only at about .047% of the alcohol in the body. Think of it like estimating the height of a building by measuring the size of a single brick. Imagine how far off the height estimate would be if your brick measurement was off by a fraction of an inch. Since the exchange ratio is so high, even small differences among how people process alcohol can have a big impact on how the breath sample corresponds to the alcohol in the body. Further complicating issues, the Intoxilyzer uses proprietary software and secret formulas to do these calculations so we don’t know what assumptions the machine makes or how exactly it calculates an alcohol result.

Maine’s OUI laws used to require proof of a “blood alcohol concentration” of .08g per 100 ml of blood or more and so breath tests were expressed in those terms. But defense attorneys won a lot of cases by pointing out the problems inherent in using breath tests to prove a blood alcohol level. Rather than fix the testing methods, the legislature changed the law and now, Maine is a “breath alcohol” state. Today, if the breath alcohol concentration is at or above .08 grams per 210 liters of breath, the person can be convicted of Operating Under the Influence.

Even with the newer breath alcohol standard and the newer intoxilyzer 8000 machines, breath test results are still open to attack. I believe that in trading blood for breath the State has just swapped one kind of problem for another. Though the prosecution no longer needs to worry about the 2100:1 ratio, it now has to deal with finding one tiny drop of alcohol (.08 grams) in huge amount, (210 liters or over 55 gallons) of breath. Click the following link for details about how I have used these issues to win at trial even in OUI with a .20 intoxilyzer test.

How to Read the Intoxilyzer 5000 Result Sheet

Intoxilyzer 5000EN Result

The following explains the testing process and what the entries on the result sheet mean. I have annotated a copy of an Intoxilyzer 5000EN result print out with numbers that correspond to the paragraphs below. Click the image to open a larger version in a new browser window.

1. The testing process begins when an individual is arrested and brought to some waiting area, often seated at the Intoxilyzer machine. Procedure requires a 15 minute deprivation period where the individual must be continuously observed and cannot eat, drink, burp, vomit or do anything else that might introduce stomach contents into the person’s breath. This time period allows any residual liquid alcohol to evaporate. Any foreign objects must be removed from the mouth as they can trap liquid alcohol and contaminate the test. During the 15 minutes, the machine will perform several internal tests.
2. First the machine will draw an “air blank” which is simply room air flushed through the machine to clear the sample chamber.
3. The machine then runs internal checks on three transparent filters which are designed to absorb an amount of light corresponding to an alcohol level of .1 .2 and .3% alcohol. The machine is checking to ensure that the sensor to returns an alcohol value within 5% of those amounts.
4. The machine then pulls another air blank to flush the sample chamber.
5. It then does a calibration check on a water and alcohol solution kept in the machine at a concentration of .09% and warmed to human body temperature. The result of this check must be within .01 of the known .09 value.
6. The machine then draws another air blank and is ready for the first subject breath test.
7. Once ready, the Intoxilyzer allows three minutes for the subject to produce an acceptable breath sample. The sample must have sufficient flow rate over at least 4 seconds and must total at least 1.1 L in volume. The Intoxilyzer needs two sufficient samples to produce a result. This first sample must be introduced at least 15 minutes after the wait period began.
8. After the first sufficient sample, the machine will flush twice with two air blanks.
9. A Second sample in introduced no less than two minutes after the previous test. Again, there are 3 minutes in which to produce a sufficient sample.
10. Once two valid samples are received, the machine adds them together, divides by two and drops the third digit after the decimal point to give a result. For the machine to accept the two tests, they must be within .02 of each other.  A variation greater than that suggests that the breath may be contaminated with mouth or stomach alcohol or that there is some other problem.

As you can see, there is a lot more to the Intoxilyzer 5000 breath test than just the result printed on a sheet. If the machine is not functioning properly, or if the officer does not follow procedure, the test result should not be accepted by the court. If you have a test print out, compare it to the one above. If you see significant differences, there might be an argument that the test should be excluded.  You can review the following articles for more information about Maine Operating Under the Influence Law:

Further reading on Maine OUI Law

• Maine OUI Laws: Elements of the Crime and Penalties if Convicted
• Maine Operating Under the Influence (OUI): Charges & Defenses
• Can I Visit Canada with an Operating Under the Influence Charge?
• Portland Maine Intoxilyzer 5000: Inaccurate for Months, Replaced
• Maine’s Operating Under the Influence Statute (State Legislature Site)
• A page with links to all my  OUI Articles