Most of us know that the legal limit in Florida is a .08. But how many of us really know what that means?
The legal description is 0.08 or more grams of alcohol per 210 liters of breath. Thus, if the breath machine registers a person’s breath alcohol level to be at or above this threshold, the state will attempt to admit this evidence at trial against the accused. But just how does the breath machine work and how does it analyze one’s breath for alcohol concentration? The only goal of this article is education, not to sway your thinking one way or the other on the accuracy of the breath machine. Of course, we can only touch on the basics of breath testing, as it’s impossible to cover everything in one article.
Although we must talk a little physiology, I’m going to merely skim the surface here because I don’t want your eyes wandering off to the next page just yet. The way that alcohol molecules find their way into your breath is through a process known as diffusion. This is where alcohol in the blood travels to the breath via the alveoli (thin-walled sacs that fill the lungs). The goal is to try and obtain, through exhalation, deep lung air from the subject.
Reliability of the sample, however, could be compromised where residual alcohol in the mouth is present, which could result in a false positive result. Breath test operators attempt to reduce this possibility by performing what is known as the “20-minute observation” to ensure against regurgitation, which causes alcohol to travel up into the mouth area.
In Florida, the police must collect two breath samples that are within a .02 agreement of each other. Thus, where the first test registers a breath estimate of .10, the second sample can be as far off as a .08 or a .12 and the estimates are deemed valid. The two samples do not (and rarely are) need to be the same. To give you a real-world analogy, this is akin to buying a scale for your bathroom, taking it home and getting on it and it says you weigh 100 pounds. Then you step off, step back on and it then says you weigh 120 pounds. Is that an acceptable range of accuracy?
The breath machine uses infrared light absorption to analyze the breath sample. Once the breath sample moves through the breath tube and into the sample chamber, the alcohol molecules will begin to absorb portions of the infrared light. The more alcohol molecules there are in the sample, the more light will be absorbed, which in turn will trigger a higher breath alcohol estimate.
Devices such as cell phones cannot be anywhere near the breath machines while a test is being conducted due to the radio frequency interference that may also compromise the test. Thus, if an officer inadvertently leaves his/her phone in their pocket while in the breath test room, reliability issues could surface.
Other issues that may call into question the accuracy of the test are “purge fails.” This is where the machine was not able to clear the sample chamber of a breath or control test sample before the next test is run. If the problem is not identified, the results of any subsequent tests would be invalid. Although the machines are in theory supposed to be able to safeguard against these issues (through display messages), that does not always occur.
A person arrested for DUI in Florida has the right to request the more reliable blood test if they first agreed to the breath test. Otherwise, blood tests are generally only obtained where there is an accident involving serious injuries or death. Simple misdemeanor DUI cases will rarely involve a blood test unless the circumstances are such that the administration of a breath test is impossible or impractical.
In sum, it’s important to understand the inner workings of the breath machine before deciding whether you should blow. Although your license will be suspended if you refuse, your license will also be suspended if you agree to the breath test and you blow over a .08. Of course, the best advice I can give anyone is to never drive impaired. That way you can forget all this science talk!
