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Measuring breath test reliability in Pennsylvania

Although breath test devices are used by Pennsylvania law enforcement agencies, their results are not always accurate and may lead to wrongful charges.

Pennsylvania motorists who have been pulled over on suspicion of drinking and driving may have been asked to submit to a breath test. It isn't uncommon for law enforcement officers to use breath test devices as a way to measure drivers' blood alcohol content levels. However, many studies show that breath analyzers are not always accurate, which may lead to a wrongful arrest and possible DUI conviction.


When administering breath tests, law enforcement officers will ask drivers to blow into a tube that is connected to the device, according to the Century Council. The breath sample is then analyzed for alcohol content and is converted into a blood alcohol content level. It is with this BAC level that officers determine whether a motorist is driving over the legal limit, which is 0.08 percent in Pennsylvania.


In addition to alcohol, breath test devices measure a number of other substances that are commonly found on a person's breath, according to a study performed by the State University of New York at Potsdam. Most breath analyzers are designed to measure the presence of ethyl alcohol in a breath sample. Yet substances that contain a methyl group structure, which is extremely similar to the ethyl group structure, may also be read by the device, which can alter the BAC reading.

The study found that there are many factors that can affect a breath test reading, including the following:

  • Gasoline, paint and paint remover fumes in the air.
  • Police radio and cellphone interference.
  • High amounts of dirt, tobacco smoke or moisture in the air.
  • Presence of vomit or blood in the mouth.
  • Extreme amounts of physical activity that cause hyperventilation.
  • Amount of cell volume a person has in their blood. People with low hematocrit levels may show a higher BAC level.

If breath test machines are not properly calibrated to account for the correct air temperature, hematocrit and several other details, the machine may give a false reading as well.


If you have been charged with drinking and driving and were given a breath test in an attempt to calculate your blood alcohol level, you may want to contact an attorney for legal assistance. A criminal defense attorney can explain all of your rights and options when it comes to fighting a DUI charge in Pennsylvania.