Class learns biomedical engineering behind breathalyzer tests

Samera Zavaro, far left, a forensic scientist with the Tennessee Bureau of Investigation, talks about breathalyzer tests while waiting to administer one to a student chewing crackers. (Heidi Hall/Vanderbilt University)

Students in a biomaterial manipulation class got an inside look at a piece of equipment they hope they never experience outside the lab.

Samera Zavaro, the Tennessee Bureau of Investigation forensic scientist charged with training officers on breathalyzer tests and ensuring the instruments’ calibration, demonstrated one Monday – with students chewing yeasty crackers and dipping their tongues in mouthwash to get readings.

“We have to make sure the instrument we send to the field is one police officers can use easily,” she said. “We also have to make sure the instrument stays calibrated, and we can testify to that.”

Zavaro routinely is called to testify in driving-under-the-influence cases — she addresses the state’s instruments’ accuracy — and her presentation revolved around that topic.

The TBI’s breath test instrumentation is calibrated every Sunday using a dry gas standard: an internal tank containing a mixture of ethanol and nitrogen gas. It uses fuel cell sensor technology to capture samples, which must be taken under specific circumstances – by law, the officer must observe that the subject has had nothing in his or her mouth for at least 20 minutes. That means no food, drink or vomit, Zavaro said.

Officers then perform two breath tests two minutes apart. “The lower result is the one that’s used,” she said.

The reason breath captures alcohol usage is because the layers of cells lining the alveoli and the surrounding capillaries in the lungs are very thin, and the air-blood exchange allows for detection, she said.

In addition to taking breath tests, students got to see the engineering inside the instrument and ask questions about how it works.

The biomaterial manipulation class is an elective taught by Amanda Lowery, assistant professor of the practice of biomedical engineering. Coursework includes application of mechanics and materials principles to medical and consumer products. Students also complete laboratory exercises in tissue culture, microscopy, mechanical testing, biochemical assays and computer modeling.


Heidi Hall, (615) 322-6614
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