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Mythbusters: Blown away: defeating the breathlyser

aug 2009 defeating the breathalyser

Mythbusters have some bad news for drivers keeping breath mints in their glove box for that special occasion when they’re invited to speak into the machine. Drinking and driving is bad enough, but if you think you can beat a breath test, you’re even more of a bloody idiot.

High profile enforcement is an important component of laws designed to reduce the harms from drinking and driving. Breath alcohol testing gives police a quick and relatively non-invasive way of detecting whether people are driving under the influence of alcohol. Yet, almost immediately since their introduction, people have claimed to be able to defeat such tests.

In one of the more unusual cases, an Alberta, US, courtroom heard how a 28-year-old man, who was stopped on suspicion of driving while under the influence, ate his underpants in the belief they would soak up the excess alcohol in his system. Arresting officer Constable Bill Robinson says he heard “some ripping and tearing” from the back of his vehicle.

“I looked in the back and he was tearing pieces of the crotch of his underwear out and stuffing them in his mouth,” he testified.

The accused was eventually acquitted because he had passed the breath test, but we doubt eating his undies was a contributing factor.

In Ontario, Canada, a 59-year-old suspected drunk driver tried to foil a police breathalyser by even more bizarre means – stuffing his mouth full of faeces. He had been taken to the police station for testing, where he grabbed a handful of his own waste “and placed it in his mouth, attempting to trick the breathalyser machine”, according to Sergeant James Buchanan of the South Simcoe Police. It didn’t work. The machine registered two readings of more than twice the legal blood alcohol limit, and the man was charged with drunk driving. In 2003, our friends at Discovery Channel’s Mythbusters tested various commonly suggested ways to defeat a breathalyser, including eating breath mints, sucking on a penny, eating an onion and drinking mouthwash. None were found effective.

Underlying many spurious claims is a lack of understanding about how testing devices work. Although breath mints might mask the odour of alcohol on the breath, they do nothing to affect blood alcohol concentration (BAC), the only thing that really matters. Alcohol shows up in the breath because it is absorbed into the bloodstream rather than being digested. As blood flows through the lungs, some of the alcohol moves from the lungs’ alveoli into the air. The amount is directly related to BAC and can be measured accurately during exhalation.

Three main types of breath testing devices are in use – those that detect alcohol by a chemical reaction producing a colour change, those relying on a chemical reaction in a fuel cell and those using infrared spectroscopy.

Interestingly, substances that may have a theoretical basis for reducing breath alcohol concentration were not tested in the Discovery Channel episode. These include a bag of activated charcoal concealed in the mouth, an oxidising gas to fool a fuel cell type detector or an organic interferent to fool an infrared absorption detector.

However, none are likely to be practical, let alone guaranteed to work.

“I’m not sure that activated charcoal would remove much of the alcohol from a person’s breath,” says Dr Richardson of the University of Saskatchewan’s Department of Pharmacology. “You would have to be blowing into the breathalyser through a mouthful of activated charcoal. The authorities wouldn’t allow this. They don’t even allow you to chew gum during these tests.”

Failure to fool a breathalyser doesn’t mean that testing devices are always 100 percent accurate. Small false positives have been recorded immediately after the consumption of various foods and soft drinks, and after the use of mouthwash.

Breathing patterns also have an effect. According to Michael Hlastala, Professor of Physiology and Biophysics and of Medicine at the University of Washington, “The most overlooked error in breath testing for alcohol is the pattern of breathing.”

He says that alcohol concentration in the first part of a breath is much lower than the equivalent BAC, whereas that in the last part of a breath is much higher.

In real life, false positives are rare. A recent New Zealand study of paired blood and breath alcohol concentrations in over 11,000 drivers found a false positive rate of only 0.14 percent.

In light of the available evidence, we conclude there is no reliable and practical way of defeating a breath alcohol test.

But getting arrested is not the biggest risk of driving intoxicated – it’s getting killed or killing someone else. The best way to beat a breathalyser? Don’t drink and drive.

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