Monthly Archives: December 2004
In my post "Why Breathalyzers Don’t Measure Alcohol", I mentioned one of the many reliability problems breath machines have: they will falsely report any of thousands of chemical compounds as "alcohol". Scientific studies have clearly proven this defect, referred to as "non-specificity".
In "Driving Under the Influence of…Gasoline?", I gave a practical example of one such compound. Is gasoline the only chemical product that has been proven to falsely register as alcohol on these machines? Far from it. See, for example, "The Response of the Intoxilyzer 4011AS to a Number of Possible Interfering Substances", 35(4) Journal of Forensic Sciences 797, where researchers found numerous common substances which were falsely reported by breathalyzers as alcohol — including methyl ethyl ketone, which is used in lacquers, paint removers, cements, adhesives, celluloid and cleaning fluids. Another compound, toluene, also caused false high readings and is commonly used in paints, lacquers, varnishes and glues. A third chemical is isopropanol, commonly known as rubbing alcohol. Fumes from these chemicals can be inhaled or absorbed through the skin.
In an interesting scientific study, researchers performed tests on a professional painter who was exposed to lacquer fumes under controlled conditions. In the first test, he sprayed paint in a room for 20 minutes, wearing a protective mask; his blood and breath were then tested. Although the blood test showed no presence of alcohol, a breath machine (Intoxilyzer 5000) indicated a reading of .075% blood-alcohol concentration –very close to the legal limit of .08%. "Lacquer Fumes and the Intoxilyzer", 12 Journal of Analytical Toxicology 168.
Yet another scientific study discovered that diethyl ether, found in some plastics and automotive products, can be inhaled and detected by breathalyzers as "alcohol". "Diethyl Ether Interference with Infrared Breath Analysis", 16 Journal of Analytical Toxicology (1992). The researchers concluded that "the possibility of interference with an alcohol reading by ether or by other substances may therefore render prosecution more difficult if not impossible."
It’s a common situation. You’re at a restaurant, it’s been a fine meal, you’ve paid the bill and it’s time to head home. You finish off the glass of wine and head for the car.
A few blocks from the restaurant, you’re stopped for speeding. The officer smells the wine still on your breath and asks you to step out of the car. A few minutes later and you’re on the way to the police station — and a breathalyzer. But you know that you and your wife each had only two glasses of wine from the bottle with dinner. The charts say that at your weight your blood-alcohol level should be around .05%, so you’re well under the .08% legal limit, right?
Wrong: the reading is .10%, your license is confiscated and you are booked for DUI.
What happened was what the toxicologists call "absorptive stage analysis". In English, your breath sample was tested while your body was still absorbing the alcohol from the last drink. Any testing during this stage of absorption will result in falsely high blood-alcohol readings.
Explanation…..Your body will continue absorbing alcohol for roughly an hour after drinking, reaching peak blood-alcohol levels sometime before that point; the presence of food in the stomach can delay this for as much as 4 hours.During this one-hour period, the alcohol is passing from the stomach and intestine into the blood, but has not yet reached a stage of "equilibrium" — that is, uniform distribution of alcohol throughout the body.
In other words, some parts of the body will have higher levels of alcohol than others — in some cases, far higher.Since the alcohol is initially passing into the arteries, arterial blood will be much higher in alcohol content than will venous blood.
Where does the alcohol come from that is being measured by the breathalyzer?
That’s right: the arteries.
Arterial blood bathes the alveolar sacs of the lungs, and alcohol diffuses into the lung air — to be breathed out into the breathalyzer mouthpiece. As one of the most noted experts in the field of forensic toxicology has observed: "Breath is not a reliable means of estimating a subject’s BAC (blood alcohol concentration)…
There is a significant likelihood that a given subject will be in the absorptive state when tasted under field conditions. Because of large differences in arterial BAC and venous BAC during absorption, breath tests consistently overestimate the result that would be obtained from a blood test — by as much as 100% or more." Simpson, "Accuracy and Precision of Breath Alcohol Measurements for Subjects in the Absorptive State", 33(6) Clinical Chemistry" 753.
In other words, if you take a breath test within an hour or so after your last drink, you will have a false high reading — possibly twice as high as your true blood-alcohol level.