Happy Halloween Now Just Breathe! Understanding a Breathalyzer & “Henry’s Law”

While the use of breathalyzers in DUI prosecutions are steadily declining due to recent Court decisions questioning their validity it is still in use by a number of law enforcement departments including the City of Philadelphia Police Department.

In Pennsylvania, the District Attorney does not actually need a person’s blood alcohol content (BAC) to prove a DUI charge as there are lesser included charges within this broad topic. A DUI charge, however, supported solely on the observations of the police officer or an eyewitness are the least serious offenses and carry the lowest penalty. For example, a first offense “observation” DUI charge (3802(a)(1)) will not result in a license suspension provided that the individual did not cause an accident or an injury. All other DUI charges with exception to a refusal of a chemical test require that the District Attorney’s Office establish that a person’s BAC exceeded the legal limit of .08 beyond a reasonable doubt.

While a blood draw is the best method to obtain a person’s blood alcohol concentration, a breath test is obviously much more convenient and does not require any outside personnel. Further, police can receive the results in a matter of minutes as opposed to days or weeks. There are also practically no issues regarding the chain of custody since the alleged drunk driver provides a sample directly into the device. A breath test is much less intrusive as it only requires two long breaths into the machine as opposed to a needle into a vein and an injection area cleansing process. In addition to all of these issues, police are under a time constraint following the arrest; the law requires that they administer the test within 2 hours of the arrest. While there are exceptions to this time rule it is the policy of most departments to avoid such an issue.

Since the law is interested in a person’s blood the breathalyzer test, by its very nature, operates on a series of assumptions, variables, and constants to arrive at a BAC level based on the alcohol concentration found in a person’s breath. Breath alcohol analysis is based on a scientific principal known as “Henry’s Law”. Henry’s Law basically states that when a liquid that contains a volatile substance, such as alcohol, makes contact with air in a closed container (breathalyzer) the amount of alcohol in the air and the liquid are static (consistent or unchanged). Breath testing devices measure the amount of alcohol found in a person’s breath and multiplies it by a predetermined coefficient to derive a person’s BAC.

This predetermined coefficient is 2100:1 blood/breath partition ratio and is based on a statistical average. While this coefficient has created litigation and has caused many law enforcement departments (including the Pennsylvania State Police) to do away with breathalyzers it remains a scientifically accepted number. The coefficient is actually lower than what the majority of individuals’ blood/breath partition would be if tested (the average blood/breath patrician is actually closer to 2300:1).

Pennsylvania continues to recognize breath tests as a valid method of obtaining a person’s BAC. While the recent case of Commonwealth v. Schildt called into question the reliability of a breath test that exceeded .15 or one that was below .05, the Pennsylvania Superior Court reversed the trial court’s decision and found this to be a trial issue. Further, the Pennsylvania Supreme Court declined to hear the appeal. There is therefore no clear answer on this issue and so it up your attorney to argue a breath test’s validity at trial using this history.

In addition to issues regarding coefficients and the calibration of the actual device, a proper defense must attack police procedure prior to the test’s administration. The prosecution must establish, by a preponderance of the evidence, that a person was observed for at least twenty (20) consecutive minutes prior to the test’s administration to ensure that the person did not ingest any fluids, regurgitate, eat, or smoke anything that could influence the test results. If residual mouth alcohol is carried into a blood sample it could increase the BAC and therefore invalidate the test.

It is also important that the defense review the operating procedure, the calibration, and the inspection requirements for the device and ensure that it is on the list of devices approved by the Pennsylvania Department of Health. Despite its decline in popularity, the breathalyzer remains an accepted method of establishing a person’s BAC and your attorney must understand this device and its issues to effectively defend you at trial.

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