Breathalyzers – What They Are, How They Work, and Their Lack of Accuracy

 

Most people are aware of the use of a breathing test by police to determine if a person is guilty of Driving Under the Influence (DUI).  However, most people are not aware of the how these devices work or their lack of accuracy.  While the breath test is usually the main piece of evidence used to arrest a person, it may surprise you to find out about the flaws in this type of testing device.

 

What is a Breathalyzer?

The breathalyzer is a common name that refers to a machine first developed by the firearm manufacturer Smith and Wesson.  The device measures the amount of alcohol in a person's blood steam through a breath sample.

 

How does a breathalyzer work?

On the machine is a tube in which a suspect blows air.  Inside are vials containing chemicals.  If alcohol is present in the breath the chemicals will turn a particular color.  A true breathalyzer is a rather large machine.  Smaller units, often called preliminary breath tests (PBT) are used by officers in the field to determine if a person should be arrested.

 

Problems with Breathalyzer: Ratios

While breathalyzers are used to calculate blood alcohol content (BAC) there is a fundamental problem with the ratio calculation.  When the breath sample is obtained from the suspect, the amount of alcohol is multiplied by 2100.  This number comes from a scientific average in which it is assumed that the body contains 2100 units of alcohol within the bloodstream for every one unit of alcohol found in the suspect's breath.  This ratio is called a “partition ratio.”

However, test data has shown that the number of units in the bloodstream can range from a low of 900 up to a high range of 3500.  So what does that mean in simple language.  For someone that has a partition rate of 1400, which is much lower than the average of 2100, they will show a BAC much higher than the legal limit simply because their body is different from the scientific average.

 

Problems with Breathalyzer: Testing Early

Another common problem with breath tests is the timing of the test.  Suppose a man shares a bottle of wine with his date over dinner.  He sips on his first glass for an hour.  The gentleman decides to pour a second glass and finishes it in short order.  The couple choose a nice after dinner drink to finish their desert.  Looking at his watch the man quickly gulps down the glass and heads for home.  A police officer stops the man within a few blocks of the restaurant.  The field breath tests shows that his BAC is .09, way above the legal DUI limit and he is arrested. 

Yet, a blood alcohol test likely would have shown the man's BAC to be around .05, which is below the legal limit.  What is the difference?  Alcohol is absorbed into the body from 45 minutes to two hours after eating.  Food in the stomach can slow this process down even more.  While the blood is working its way through the body it is not absorbed in a uniform manner.  In plain words, certain parts of the body will have more alcohol than others.

 

Problems with Breathalyzer: They Don't Test For Alcohol Only

The biggest problem with breathalyzers is the main focus of most DUI lawyers’ legal challenges to the device.  Breathalyzers do not measure the amount of alcohol present in the body.  The machine actually picks up and then measures anything in the breath that contains a certain methyl group within the chemical makeup.  Many compounds that are found within the human body contain this methyl group and therefore report them as alcohol incorrectly.

To prove a point, researchers conducted a test among 8 adult males and found 69 various compounds that had the methyl group.  A breathalyzer would have picked up all of these compounds as alcohol in the bloodstream.

 

What should you do if you’ve been arrested and have taken a PBT or breathalyzer test?

Based on this overwhelming evidence most DUI lawyers take the position that their clients should refuse a field sobriety test.  Refusing the test will usually result in an arrest and a trip to the police station.  But it gives the suspect an opportunity to contact their attorney and get proper legal advice before taking any more action.