A few things to know before taking a DUI breath test

In South Carolina and across the nation, breath test results are one of the most widely used pieces of evidence in drunk driving cases. As a result of their importance in prosecuting DUI suspects, there are many tips circulating on the Internet and elsewhere that offer advice on fooling the machine into registering a lower blood alcohol content (BAC). Although most such tips are myths, one factor can influence the results of the breath test, although not always in your favor.

According to studies, how you blow into the machine can affect the results of a breath test. Breath test machines work by measuring the BAC of a person’s breath. When a person has been drinking, there is more alcohol at the bottom of a person’s lungs than at the top. As a result of this biological fact, a person who holds his or her breath before blowing into the machine can increase the BAC reading by as much as 15.7 percent, as the inhaled air has more time to become saturated with the alcohol in the lungs. A person who hyperventilates before the breath test, on the other hand, can decrease the BAC result by 10.6 percent.

Unfortunately, police offers often take advantage of this fact when administering blood alcohol tests to arrest as many drivers as possible. They do this by asking DUI suspects to take a deep breath and to blow as hard as possible into the machine. As a result of these instructions, more alcohol-rich air is exhaled, resulting in a higher BAC (and a higher likelihood of a DUI arrest).

Protect yourself

In reality, breath test machines only need about seven seconds worth of breath to test a person’s BAC. Additionally, the machines do not require a person to blow exceptionally hard to arrive at a result. To ensure that the BAC level is not influenced, it is important to remember the following when taking a breath test:

  • Blow into the machine at a normal rate as you would through a straw for about seven seconds.
  • Do not hold your breath or take a deep breath before blowing.
  • Let the police officer know before the test if you have any medical conditions that would prevent you from blowing steadily into the machine.
  • Always ask for a copy of the results.

In South Carolina, when an officer incorrectly administers a breath test, it is grounds to have the test results thrown out. In a 2013 DUI case, a Columbia, South Carolina, municipal judge ruled that the breath test results were inadmissible because the officer in the case instructed the suspect to “blow hard” into the machine. Although this particular case is not binding on other jurisdictions, it illustrates the importance the law puts on proper police procedure in DUI prosecutions.

If you have been arrested on suspicion of DUI, it is important to contact an experienced criminal defense attorney as early in the process as possible. An attorney can investigate the circumstances of your arrest and prepare an effective defense on your behalf.