How Accurate Is a Breathalyzer Test?

Drunk driving kills. About half of alcohol-related traffic deaths involve at least one driver with a blood alcohol concentration (BAC) of 0.16 or above. A large number of high-BAC offenders repeat their offenses. Roadside testing with a breathalyzer has been relied upon since the 1950s as a method of gathering evidence to keep them off the streets. Even so, it must be noted that there are scores of factors that affect the reading garnered by a breathalyzer test; science has determined that the breathalyzer's many opportunities for inaccuracy make its evidence imperfect at best and illogical at worst.

History

• In 1927, a scientist named Emil Bogen ran a study in which he had an arrested subject fill a football with air from his lungs, and then tested the air inside the football for alcohol. The resulting paper noted that, of the two liters of air in the football, there were about 1.5 cc's of alcohol present. The first roadside BAC testing kit debuted in 1938. It was an unwieldy instrument called the "Drunkometer," and involved a subject filling a balloon with air from the lungs and running that air through a solution (which would change color according to the amount of alcohol in the air.) The breathalyzer as we know it now was invented by Dr. Robert Borkenstein in 1954. Though new versions have replaced his chemical oxidation and photometry with an infrared process, the portability of the device and its immediate delivery of results made the breathalyzer the standard in BAC testing for law enforcement

Considerations

• Errors and the opportunity for inaccurate breathalyzer testing abound. If a subject is tested too close to the time when he drank, there's a good chance the alcohol has not been fully absorbed. Since alcohol absorption is a process that takes from 45 minutes to two hours or more--and, during this phase, BAC will vary widely from body part to body part--BAC in the arteries can be as much as 60 percent higher than the level in the veins. Other factors affecting breathalyzer accuracy include miscalibration of the device, false assumption of the test subject's hematocrit level, the level of alcohol present in the subject's mouth, the breathing pattern of the subject, operator error on the part of the tester and interfering compounds in the subject's blood (that is, acetone in the blood of diabetics). These factors can greatly affect the result of the breathalyzer test.

Misconceptions

• Many people believe that breathalyzers can be fooled into delivering inaccurately low results if the subject ingests certain substances. On the Discovery Channel show called "MythBusters," a group of these substances (mouthwash, breath mints, fresh onion, denture fixative, penny coins and batteries) were tested systematically against the breathalyzer test. None were shown to effectively lower the BAC reported by the breathalyzer.

Warning

• While some substances are falsely believed to lower the BAC detected by a breathalyzer, there are some substances that are proven to significantly raise the levels. Some alcohol-containing mouthwash, for instance, has just under 30 percent alcohol content; if the subject uses the mouthwash according to the directions on the package directly before a test, the breathalyzer will calculate its reading as though all of that alcohol is in the blood. These readings routinely show BAC beyond lethal levels, even though the subject had not ingested any recreational alcohol. The mouth alcohol that causes the error will generally dissipate within five minutes. Similar high-side inaccuracies have been reported in conjunction with breath sprays.

Potential

• The calling into question of breathalyzer accuracy has spurred a handful of state supreme courts to rule that defendants may challenge their results. The basis of California's 2009 ruling hinged on the fact that the tests don't accurately test every subject in the same way--there's too much variation from person to person (and even place to place, as far as atmospheric factors are concerned) for the decimal-point levels to be truly scientific. Supreme courts in Arizona and Vermont have ruled similarly, and cases are emerging in other states as well. Prosecutors worry that this trend in the justice system, because it calls into question some of the basic evidence they are given to argue, will have a detrimental effect on their ability to convict drunk drivers.