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How do preliminary breath testing instruments work?

The National Highway Traffic Safety Administration is always on the lookout for technology that can help authorities in every state, including Maryland, get drunken drivers off the road. One recently developed testing device that is more accurate than current breathalyzers detects the blood alcohol content contained within the alveoli of a person's lungs. The alcohol is typically exhaled during a test, allowing a law enforcement officer to measure a driver's blood alcohol level.

According to NHTSA, three types of preliminary breath-testing instruments are now being used around the country, including in Maryland. In most states, guidelines and legal grounds for the use of these devices are already written into implied consent laws.

The three different types of PBT instruments are electrochemical, semiconductor and disposable chemical. In electrochemical PBTs, alcohol vapors from a driver's breath are absorbed by a fuel cell where it oxidizes to produce an electrical current. The amount of current produced by the reaction indicates the BAC percentage. A semiconductor PBT instrument works in a similar fashion, detecting BAC based on the amount of produced current. Disposable chemical PBTs have a measured amount of chemical in a glass or plastic tube that reacts with the alcohol. Exhaled breath with alcohol reacts with the chemical.

Other types of BAC instruments include wet chemical instruments and noninvasive or passive alcohol sensors. Use of the latter does not require consent from a driver because the sensors pick up breath alcohol inches away from a driver's face and allows officers to quickly determine if a driver should be detained further.

Maryland drivers should understand that breath test results are often crucial evidence in any DUI hearing. However, these tests do have potential to be corrupted or fail in ways that may skew the findings and negatively impact the driver in question. Seeking the assistance of a reputable attorney familiar in such cases can help explore the incident to a full extent, possible unearthing defenses along the way and helping to protect the rights of the driver.

Source:, "The Highway Safety Desk Book," Accessed on Feb. 5, 2015

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