Payson Blood Alcohol Concentration (BAC) Testing

A person’s blood alcohol concentration, or BAC, is often considered by prosecutors and police officers to be one of the strongest pieces of evidence in a DUI case. However, there are several factors that could lead to inaccurate BAC testing in Payson. Mishandling or contamination of blood samples, malfunctions with BAC testing devices, and user error all may lead to erroneous BAC results that are used to file DUI charges against you.

If you are arrested for a DUI in Payson, you should immediately request to speak with an attorney before consenting to any BAC test. We have attorneys available 24/7 to take your call and guide you through the process. Call 480-248-7666 any time, day or night, to speak with an attorney.

If you have already been charged with a DUI in Payson and the police took a blood or breath sample from you for BAC or drug toxicology testing, you will need an attorney that is ready and willing to challenge the reliability of the government’s tests.

Types of BAC Testing

The most common types of BAC testing used in Payson DUI arrests are “Intoxilyzer” (breathalyzer) and headspace gas chromatography testing (blood testing). Officers will take blood or breath samples to determine a person’s BAC. There are several precautions that need to be taken when administering and analyzing these tests. If police or lab technicians cut corners, BAC results may be skewed. We work with experts in forensic toxicology to stay up to date on the latest issues in the field so that we can mount aggressive defenses based on cutting-edge scientific data.

Payson BAC Testing Attorney

Portable Breath Test (PBT)

In many DUI cases, a person completes a breath test with a small handheld device on the side of the road. This device is a Portable Breath Test, or PBT. It takes one breath sample and uses that to give an estimate of a person’s BAC. It is important to know that you are not required to submit to a PBT test.

Many PBTs used by police officers rely on fuel cell technology to estimate a BAC, which uses an electrochemical process to oxidize the alcohol in a person’s breath sample. This produces an electrical current which the PBT reads and uses to calculate a person’s BAC, which is then displayed on a small screen. Officers use these devices because they are quick and easy, giving them a BAC estimate in a matter of seconds. However, quick and easy is rarely a good thing when it comes to the criminal justice system. PBT devices are very rudimentary and often produce wildly inaccurate results. In fact, a BAC determined by a PBT is not admissible in Arizona courts, it is essentially only used by police officers to make arrest decisions out in the field. So, if you were given a PBT on the side of the road, whatever result was displayed on the device’s screen will not be admissible against you in a criminal trial.


The Intoxilyzer is a breath testing device manufactured by a company called CMI. This is a much larger machine than a PBT and is often kept at the police station or in a dedicated DUI van. Unlike the PBT, a BAC determined by an intoxilyzer is typically admissible in a criminal case. A person blows two separate times into a flexible tube connected to the device and the machine produces two BAC readings by using infrared spectroscopy.

To boil it down to a basic explanation, a person’s breath travels through a chamber in the machine and infrared light is passed through the breath sample. Across from the infrared light emitter is an infrared sensor. Alcohol molecules are known to absorb a certain amount of infrared light. Therefore, as your breath passes through the chamber, if there is alcohol in your breath, infrared light will be absorbed before reaching the infrared sensor on the other end of the chamber. The intoxilyzer then calculates the amount of infrared light that was absorbed by the alcohol molecules in the person’s breath to determine a BAC.

Challenging BAC Test Results

Calling the results produced by this machine a “BAC” is a bit of a misnomer, because this machine is incapable of testing your blood. An intoxilyzer is calculating a BAC, or Breath Alcohol Concentration.

While this equipment may seem much more scientific than a PBT, it is not without its pitfalls. There are several defenses employed by the attorneys at the Rosenstein Law Group to challenge a BAC determined by an intoxilyzer.

We review intoxilyzer maintenance records to determine whether there are any known issues with each machine. Each machine will go through periodic checks from a Quality Assurance Specialist (QAS). If the QAS does not complete the required quality assurance checks properly or in a timely manner, this can be used to challenge the results or even to suppress the evidence altogether. Additionally, the two breath tests must be preceded and followed by proper air blanks and must be within .020 of each other.

The Arizona Department of Public Safety allows for a shockingly high range of accuracy for intoxilyzer machines, which is 10%. An experienced attorney will know that the accuracy of an intoxilyzer can vary by much more than 10% due to several environmental variables. Among other issues, residual mouth alcohol, a person’s breath temperature, and the way in which a person breathes into the machine can all affect the reliability of the results.

Blood Testing (Headspace Gas Chromatography)

Blood testing is now a common occurrence in DUI arrests. An officer or other qualified phlebotomist will draw two tubes of blood from an arrestee and submit the blood to a lab for testing. The testing method used throughout Arizona is headspace gas chromatography. This testing method involves a lab technician pipetting known controls and calibrators into a machine along with blood samples from people that have been arrested for DUI. The controls and calibrators are used to make sure that the machine can detect certain levels of ethanol and accurately determine a BAC.

Breakdown Blood Testing for BAC in Arizona

While the science behind a headspace gas chromatograph can be complex, it is helpful to break down the machine into more simple terms to get a basic understanding of what the machine does. The heart of the machine is basically an oven. Controls, calibrators, and blood samples are loaded into individual headspace vials, which are transferred into the machine and heated. As each vial is heated, the ethanol in the blood begins to diffuse into the gas phase until a state of equilibrium is reached between the amount of alcohol contained in the liquid blood and the alcohol contained in the gas vapor, this is based on a scientific principle called Henry’s Law.

A needle then punctures the top of the vial and draws up the ethanol gas vapor, injecting it into two columns, which are long glass tubes with a special coating on the inside. A carrier gas transports the gas vapor through the tubes. Because of their reaction with the coating in the columns, different volatiles, like ethanol, travel through the columns at different rates specific to each volatile. At the end of the columns is a flame ionization detector, which detects the ions formed by the combustion of the volatiles after they pass through the columns. By measuring the ions, the machine can calculate a BAC.

Effectively Defending Against Inaccurate BAC Evidence

This is a very abbreviated and boiled down synopsis of how headspace gas chromatography works. What is important to know is that this machine can be very sensitive to human error. While there may be problems with the machine itself that could cause accuracy issues, the danger of human error during the preparation of the samples, calibrators or controls is that it may be difficult if not impossible to detect the error by looking at the data produced by the machine after a test. This could result in erroneous BAC readings that a prosecutor or lab technician will not hesitate to rely on to prosecute you.

With a smart, comprehensive investigation into all of the aspects of your case, including the roadside field sobriety tests, driving behavior, drinking history, blood draw and toxicology testing, an experienced DUI defense attorney can mount an aggressive defense to challenge the prosecutor’s BAC evidence.

Payson DUI Lawyer – Available 24/7

The attorneys at the Rosenstein Law Group have substantial experience dealing with forensic evidence. We also work closely with leading forensic experts to mount unique defenses based on the facts of each case. A good DUI defense attorney will not only review the scientific testing data to challenge the BAC but will also use facts gathered from your roadside interaction with the police to attack the credibility of the prosecution’s BAC evidence. This comprehensive approach is necessary to get you the best possible result, which may include suppressed evidence, reduced charges, a dismissal or complete acquittal.

Contact the Rosenstein Law Group at 480-248-7666 or online for a free consultation and preliminary case evaluation.


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