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. The number produced by BAC testing devices can have a profound effect on your case, however, there are a number of factors that could lead to inaccurate BAC testing results. Mishandling or contamination of blood samples, malfunctions with BAC testing devices, and user error all may lead to erroneous BAC results that are used as evidence against you.
If you are arrested for a DUI in El Mirage, 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 El Mirage and the police took a blood or breath sample from you for BAC or drug toxicology testing, below you will find some information about the types of testing used in this jurisdiction.
The most common types of BAC testing used in El Mirage 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 a number of precautions that need to be taken when administering and analyzing these tests. If police officers 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 to DUI charges.
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 to give an estimate of a person’s BAC. While these machines are convenient for police officers, the results they produce can be wildly inaccurate. 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 a criminal trial. In Arizona, PBTs are used by officers to make an arrest decision out in the field. They are just another tool to establish probable cause for an arrest. 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 and police officers and prosecutors will rely on its results without hesitation.
During the administration of an intoxilyzer test, a person blows two separate times into a flexible tube connected to the device. The machine produces two BAC readings by using infrared spectroscopy. The breath samples are collected approximately 6 minutes apart and are recorded along with a series of internal checks in the machine. 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 measures the amount of infrared light that was absorbed by the alcohol molecules in the person’s breath to calculate a BAC. 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 actually calculating a BAC, or Breath Alcohol Concentration.
While the Intoxilyzer is considered more reliable than a PBT, it is not without its pitfalls. There are a number of defenses employed by the attorneys at the Rosenstein Law Group to challenge a BAC determined by an intoxilyzer. First, for each machine, police agencies keep maintenance records. These records will document known issues with the machine throughout time as well as routine maintenance that is supposed to be performed. Some parts in the machine wear down over time, requiring replacement or maintenance. In some cases, by reviewing the records we can find issues that were ignored or improperly handled. It is not unusual to see an officer complain of the machine producing an error code and then simply turning the machine off and back on as a quick fix.
Each machine must 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 suppress the evidence altogether. Additionally, the two breath tests must be preceded and followed by proper air blanks and the person’s BAC readings must be within .020 of each other. At times, we will see an officer simply have the person complete a third breath test is the first two were not reliable enough to produce a “successful” test sequence.
The Arizona Department of Public Safety also 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. That is to say that even if the machine produces what it labels as a “successful” test, there may be outside variables in your case that artificially inflated the BAC results.
Blood testing is now a common occurrence in DUI arrests in El Mirage. Many police officer take a course to become qualified phlebotomists. Some agencies may also use contracted phlebotomists to conduct blood draws. Either way, the police agency will attempt to draw two vials of blood from people that have been arrested for DUI. A vial is then sent to a lab for testing, while the second vial is typically held in refrigerated storage to be made available for testing by the defendant in the ensuing criminal case. The blood samples are tested for BAC using 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. While the science behind a headspace gas chromatograph can be complex, below is an abbreviated synopsis of the basic process and how it works.
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 rubber stopper on 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 is able to calculate a BAC.
The process for blood testing is more complex than what we see from the Intoxilyzer or PBT. With this increased complexity comes an increased possibility for human error, which this machine is particularly sensitive to. While there may be problems with the machine itself, such as worn out and malfunctioning equipment, which 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. The temperature of the samples and controls, storage conditions and handling of the blood samples during the pipetting process could each influence the reported results.
Issues in these areas could lead to erroneous BAC readings that a prosecutor or lab technician will not hesitate to rely on to prosecute you. That is why it is important to not only look for inconsistencies in the data produced by the machine, but also to look for inconsistencies between the reported BAC and the other facts of your case. A comprehensive defense approach will look at the roadside field sobriety tests, driving behavior, drinking history, blood draw and toxicology testing to find inconsistencies that may point to an inaccurate BAC.
At the Rosenstein Law Group, we have extensive training and experience when it comes to forensic toxicology and specifically BAC testing. We also work closely with forensic scientists to review BAC testing data to discover potential issues. We take an aggressive, smart approach to DUI defense to ensure that our clients receive the highest level of representation and the best possible outcome.