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McLean DUI Breathalyzers

Despite the potential issues with breathalyzers, breathalyzers are the main means by which persons’ blood alcohol content is determined. This is due in part to breathalyzers being much less intrusive than blood draws and easier to conduct. In addition, McLean DUI breathalyzers are tested at least twice a year for their accuracy and their error rate. Moreover, breathalyzers are serviced by the Department when they are transported for calibration.

For more information bout breathalyers and how an attorney could help you challenge a breath test result, contact an accomplished DUI lawyer.

Common Misconceptions About Breathalyzers

Some common misconceptions about DUI breathalyzers in Mclean are:

  • A Preliminary Breath Test (PBT) is equivalent to a breath test conducted by an instrument such as the Intox EC/IR II
  • That a person must submit to a PBT
  • That an individual is not required to provide a sample for the Intox EC/IR II

A PBT is a portable handheld device carried by many officers that measure the blood alcohol concentration of a person’s breath. Officers use these devices when making a probable cause determination for arrest. These tests, like all field sobriety tests, are voluntary – a person cannot legally be compelled to take a PBT.  Also, unlike Certificates of Analysis produced by the Intox EC/IR II, the Commonwealth is not permitted to introduce the results of an individual’s PBT in the prosecution for a DUI charge (Va. Code § 18.2-267).  However, there are some exceptions to this exclusion such as when the probable cause for arrest is challenged. While a person is not required by law to submit to a PBT, drivers are required under Virginia’s Implied Consent law (Va. Code § 18.2-268.2) to submit to having samples of breath taken for chemical analysis where they are physically able to do so.

False Positives with Breathalyzers

Some ways that breathalyzers can result in false positives or inaccurately high BAC reading include:

  • Presence of mouth alcohol
  • High breath temperature
  • Improper calibration or maintenance of the breathalyzer

Mouth alcohol – could result in a reading that does not accurately reflect the alcohol concentration in a person’s blood due to alcohol residue in the person’s mouth.  This is why officers are trained to have persons undergo 20 minute observation periods before taking breath samples. During this observation period, officers will be watching to determine if the individual burps or vomits, which may result in mouth alcohol.

High breath temperature – this can result in inaccurate readings because the temperature is a factor in Henry’s Law.  Henry’s law is that the breath to blood ratio is always assigned a value of 2100:1. Henry’s law assumes that under equilibrium conditions, 2100 milliliters of a person’s breath contains the same quantity of ethyl alcohol as one (1) milliliter of their blood.

Henry’s Law operates with an assumed constant temperature of approximately 37 degrees Celsius (98.6 degrees Fahrenheit). Because of this, a person having a high temperature could lead to an inaccurate reading. 

Inaccurate calibrations or maintenance – breathalyzers are machines and are subject to mechanical errors just like any other machine. 

Calibrating Breathalyzers

Some crucial issues regarding the calibration of DUI breathalyzer machines in Mclean involve improper calibration resulting in inaccurate results.

According to the Virginia Department of Forensic Science (DFS), breathalyzers should be calibrated as needed. 

Breathalyzers are typically transported to DFS’s Calibration Laboratory for calibrations every six-months. A forensic scientist tests the breathalyzers to make sure they meet all requirements for accuracy and performance according to its requirement under Virginia Code § 9.1-1101(B)(3). This statute requires the Department to test the accuracy of equipment used to test the blood alcohol content of breath at least once every six months. It further provides that only equipment found to be accurate shall be used to test the blood alcohol content of breath.

It is important to note that a defendant bears the burden of producing evidence showing noncompliance with procedural requirements such as those of § 9.1-1101(B)(3).  This means that the Commonwealth does not have to produce evidence that the breathalyzer has been appropriately calibrated. Typically, defense counsel is not provided with a calibration certificate in discovery and this must be requested from the Department of Forensic Science.  Without evidence to the contrary, there exists a presumption that the calibrations were conducted in accordance wit the law.

Challenging Breathalyzer Results in McLean

A defendant can challenge erroneous breathalyzer results in court.  This can be done at trial or pre-trial through a motion to suppress. Through a motion to suppress, defense counsel could argue that the person’s being made to submission to a breathalyzer test violated the Constitution. In a motion in limine, an attorney could argue that the breathalyzer test results should be excluded on bases such as the test not having been administered properly, the person administering the test lacking appropriate training, or the machine not having been properly calibrated.

Having an attorney who is knowledgeable of the requirements for McLean DUI breathalyzers and how to challenge errors can be the difference between a conviction with significant penalties and a dismissal.

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