DUI Breath Test Results
How to show the breath test results in your DUI case are unreliable
There are many ways to attack the reliability and accuracy of the DUI breath test results in your DUI case. This article discusses 3 of them.
There’s going to be three different problems that we’re going to be talking about that are associated with the breath testing machines. Now there are plenty more than that but we’re just going to be talking on three of them. Why are we discussing this? Because the prosecutor’s case against you gets a lot weaker when you can show that there are problems with the machine.
Before we begin our discussion you need to be aware of two things. One, the laws relevant to DUI evidence and defenses are constantly evolving. The science relevant to DUI cases is also continually developing and changing. Now that we’ve got that disclaimer out of the way let’s discuss three key problems with breath alcohol testing machines.
Number one is alveolar air. Number two is temperature and number three is breathing pattern.
DUI Breath Test Results and Alveolar Air
Let’s start with the alveolar air. You might be thinking what on earth is that? Well, I’ll tell you. Alveolar air is the air in your respiratory system that is closest to your blood. It’s at the deepest part of your lungs. For that reason we also refer to it as deep lung air.
The alcohol breath testing machines are intended to measure a person’s breath in order to get a blood alcohol concentration or BAC reading. It’s not just any old type of breath that the machines are supposed to be analyzing. They’re supposed to measure deep lung air. Deep lung air is the air in your lungs that actually interacts with the blood in your system which means measuring the amount of alcohol in the deep lung air is supposed to give us the best idea at how much alcohol is in the blood that passes right next to it. That’s what the breath testing machines are supposed to be doing. But is that really what they do? No. Not really.
Here’s what really happens. Right before you blow into the machine you take a deep breath. As you do so, air enters your mouth and then travels down your trachea and then into your bronchiole tubes. Then down into the deep part of your lungs like you see here. You’ve got the trachea, it goes into your mouth and then down into your trachea, then down to your primary bronchi, then secondary, then tertiary, down into the bronchioles and finally into these little sacks the alveoli.
An alveoli is a little sack of air. It’s estimated that there are around three hundred million of them in the average sized adult. They’re small. They’re also the place where the air meets up with the blood in your body to feed your blood with oxygen and take the carbon dioxide out of the blood. That’s where they make the old oxygen carbon dioxide hand-off.
The air says I’ll give you some oxygen if you give me some carbon dioxide. The blood says, deal. Each air sack is covered with capillaries that allow your blood and air to, in essence, rub up against each other and make the exchange. Here’s what they look like.
The idea behind the breath machines is that the blood that has alcohol in it will transfer some alcohol to the air that’s in those sacks. By measuring the amount of alcohol in those air sacks we can take an educated guess as to how much alcohol is in your blood.
But there is a big problem. The air that passed through your mouth and into your trachea can pick up tiny molecules of alcohol vapor along the way. Why? Because as you’re drinking, alcohol gets stuck in the mucous that lines your internal tubing. When the air passes, it picks up that alcohol. As you continue breathing, the air passes over that same tubing and a mucous lining and picks up those alcohol molecules. Alcohol is an extremely effective hitchhiker.
What’s more, air can only hold so much alcohol. If the air is full of alcohol when it gets to the air sacks, it won’t have any more room to pick up more alcohol from your blood. When the air travels back up the trachea into and then out of your mouth and then into the breath machine, the alcohol the machine is reading is the alcohol that came from the mucous in your mouth and trachea…not the alcohol that’s in your blood.
The alcohol in your mouth and trachea can’t make you drunk. Only the alcohol in your blood gets carried to your brain. Only the alcohol that gets to your brain can have any effect on your nervous system, your ability to think straight and drive straight.
This means that the resulting BAC of your breath test is largely irrelevant and says nothing at all about how much alcohol is actually in your blood. That’s the first weapon of mass destruction.
DUI Breath Test Results and Temperature
Onto the next defense. Temperature. The temperature of the air that’s being analyzed by the machine is crucial. Breath test machines are calibrated based on an assumed breath temperature of thirty four degrees Celsius. However, the average body temperature for humans is ninety eight point six degrees Fahrenheit which is thirty seven degrees Celsius.
Someone who has a fever will have a higher temperature and their breath temperature will also be higher. The higher your body temperature is, the less accurate the breath machine will be. For example, if you have a temperature of 104 degrees and blow on the breath test machine, the machine will give you a BAC reading that is 19.5% higher than your actual BAC is. If your actual BAC is .07%, a high temperature could result in a false reading of .08% and get you arrested.
Unfortunately, cops aren’t trained to ask if you’re running a fever. Nor do they take your temperature at the time of the arrest. Police officers and prosecutors won’t go out of their way to gather evidence that could prove your innocence. It will be up to you and your lawyer to pursue this as a possible defense in your DUI case.
DUI Breath Test Results and Breathing Pattern
On to the third method of beating your case: breathing pattern. Your breathing pattern can account for a difference between your actual BAC and the BAC reading from the breath test machine of plus or minus 50%. This is because your body’s airways are very sensitive to temperature. As you breathe in cold air, your airways are cooled off. As the warmer air inside your airways is exhaled, some of the alcohol sticks to the cooler airways. It’s somewhat similar to what happens when you breathe on a cold window. The water in your breath sticks to the window because it’s colder. What happens when the window warms up? He water molecules evaporate into the air. Right?
A similar thing happens with your airways. As you continue to exhale for an extended period of time, the warm air warms up your airways. The alcohol molecules condense and detach from your airways and get exhaled out of your mouth and into the breath testing machine. This means that when you’re blowing into the breath testing machine the first part of your breath has a lower BAC and the later part of your breath has a higher BAC. In the later part of your breath the BAC is too high because the breath is carrying alcohol from your lungs plus the alcohol it picks up from the airways which have since warmed up. The first part of your breath sample could have a lower concentration of alcohol than your actual BAC. The last part of your breath sample could have a higher concentration of alcohol than your actual BAC.
Wouldn’t you know it? The breath testing machines are designed to use the last part of your breath as your BAC level that they report. Convenient, right? When you blew into the breath testing machine did the officer keep telling you, blow, blow, blow? Now you know why. The more you kept at it, the higher your BAC was going to go. Ain’t that a dirty trick?
All of this means that your breathing pattern before you take the breath test can effect the result of the test. Breathing deeply for twenty seconds prior to blowing into the machine can reduce your BAC result by eleven percent. Holding your breath for thirty seconds can increase the result of your breath test by sixteen percent. This is because breathing deeply cools your airways and holding your breath warms your airways.
Those are the three weapons that could potentially help you win your case. You now know more about breath tests than the cop that arrested you. You learned that: 1) the breath testing machines aren’t capturing the air they think they are, the deep lung air; 2) the breath testing machine is susceptible to inaccuracies based on your body’s temperature and thus your breath’s temperature; 3) the machines are prone to inaccuracy because of differences in temperature between the air inside and outside your body which is further manipulated by your breathing pattern.
Why does all this matter? Because if you want to win your case, you’ll have to be ready to hold the government’s feet to the fire, so to speak. Make them prove their case. You, i.e., your lawyer, has got to be able to speak with the prosecutors from a position of power. Knowledge is power.
Learn more:
Court Hearing Process for DUI Cases
Field Sobriety Test Results in DUI Cases