Breath testing of drunk driving suspects has been such a commonplace practice for so many decades, most of us hardly think to consider how they work. “Breathalyzers” are just a ubiquitous part of our understanding of police work. But in light of Rochester’s Deputy Mayor Redon’s DWI arrest, it’s worth considering the technology behind the most common field science instrument in modern police work. Can they really be tripped up by something so common as diabetes? How do breathalyzers work?

The first thing to know is that “Breathalyzer” is like “Kleenex,” in that it is a brand name that has become shorthand for all products of a type. The original Breathalyzer was invented in the 1940’s by a Dr. Bob Borkenstein (giggle) for the Indiana State Police. The brand and the technology are much less used today. New technologies have pushed this most basic field unit aside in favour of more admissible evidence.

The Theory

Regardless of the technology, all breath tests are based on very simple principle. Alcohol does not break down in the body and does not get digested. It passes through the blood stream and eventually into the alvioli in the lungs, where it evaporates when it comes into contact with air. As your body takes in oxygen, it expels a tell-tale quantity of alcohol. The rate of evaporation is directly proportional to the rate of concentration in the blood, based on an 1800’s constant known as Henry’s Law.

Simply put, by measuring the amount of alcohol on your breath, police can correctly identify the amount of alcohol in your blood stream. It is a simple ratio of 1:2100, or 2,100 milliliters of breath containing the same alcohol as 1 milliliter of blood.

However, it has also been well-established for decades that certain types of blood alcohol measurement can be thrown off by the introduction of other chemicals. Specifically, acetone which is commonly found on the breath of diabetics has been shown to inflate BAC measurements.

The question is: how do you measure the amount of alcohol in the breath? Broadly, there are three types of alcohol test in common usage: chemical catalyst, infrared spectroscopy, and fuel cell technology.

Chemical Catalyst

This is the Breathalyzer system, also sometimes referred to as the “wet method,” because it relies on chemical reactions between the alcohol on your breath and potassium dichromate. Alcohol turns the normally orangeish potassium dichromate greenish, then a photocell compares the mixed chemicals with a “control group” of unmixed potassium dichromate. Officers are required to dial a knob to measure the change between the two vials and determine a driver’s blood alcohol.

This system is scientifically sound and unaffected by acetone, but legally suffers from the amount of human interaction. Since an officer is required to do the measurement, DWI cases in the past have been thrown out on suspicion of tampering. For this reason, the Breathalyzer has often been given the derisive name “Dial-a-Drunk.”

Infrared Spectroscopy

When light hits a molecule, the bonds between the various atoms vibrate. As they vibrate, they emit light, the color of which depends on how far apart the bonds get as they go back and forth. The higher the bounce, the further up that ROYGBIV scale we all know and love. By hitting an unknown substance with a predictable wavelength of light, the color change can be measured and, based on prior research, pegged to specific chemicals with known vibration rates.

This is the basis for all spectroscopy. And because these sub-microscopic light shows are so consistent and don’t require any operator interaction, they make a perfect field sobriety test. Hence IS blood alcohol testers are in extremely common use the world over.

However, it was identified in the 1970’s that acetone can interfere with a BAC test that uses spectroscopy. That is because acetone and alcohol have very similar vibration rates that can easily be confused with one another. It is estimated that the inflation can be as great as .06 BAC, which is significant.

The solution to this problem for law enforcement has long ago been to use multiple wavelengths of infrared light. Because while the single rate of vibration between alcohol and acetone may be similar, the difference between their reaction to two different wavelengths is not. Thus most modern BAC testers such as the Datamaster DMT are at least theoretically immune to this line of defense.

The New Frontier: Fuel Cell Testing

The last type of testing seems for now to have the best of both worlds: it is unaffected by interfering chemicals in any way, and requires no human measurement. That technology is a fuel cell, which like it’s budding use in automobile power, works to separate electrons from a substance. In this case however, it separates the subject’s breath and instead of using the electrons to power a car, it measures the number to determine if alcohol is present.

The only trouble, as recently as two years ago, with using this type of technology is that the fuel cells may not last very long or very consistently. In Minnesota, defense lawyers effectively halted their use because of these problems.

So, diabetes and DWI? No luck?

Sorry, no. While it is certainly true that the single most commonly-used technology in BAC testing by law enforcement is the one technology that is subject to this flaw, the kinks have long-since been ironed out. The New York State Troopers that pulled Mr. Redon over use Datamaster DMT breathalyzers for the court-admissible sobriety test and those devices definitely use multi-wavelength testing.