Breathalyzer

A breathalyzer (or breathalyser) is a device for estimating blood alcohol content (BAC) from a breath sample. "Breathalyzer" is the brand name of one manufacturer of these instruments, but has become a genericized trademark for all such instruments. Intoxilyzer, Alcosensor, Alcoscan, and BAC Datamaster are other common brand names.

Breath analyzers don't actually test blood alcohol content or concentration, which requires the analysis of a blood sample. Instead, they estimate BAC indirectly.

Two technologies are in use: a spectrophotometer that is used by police forces to detect the amount of alcohol in one's breath during evidential breath testing, and fuel cell-based instruments that are used at roadside screening.

Different types of machine use different techniques and larger machines generally yield better estimates than do hand-held models. Therefore, some states don't permit data or "readings" from hand-held machines to be presented as evidence in court. South Dakota does not permit data from any type or size breath tester but relies entirely on blood tests to ensure accuracy.

Common problems

A major problem with some machines is that they not only identify the ethyl alcohol (or ethanol) found in alcohol beverages, but also other substances similar in molecular structure. Those machines identify any compound containing the methyl group structure. Over one hundred compounds can be found in the human breath at any one time and 70 to 80 percent of them contain methyl group structure and will be incorrectly detected as ethyl alcohol. Importantly, the more different ethyl group substances the machine detects, the higher the false BAC estimate will be.

The National Highway Traffic Safety Administration (NHTSA) has found that dieters and diabetics can have acetone levels hundreds and even thousand of times higher than those in others. Acetone is one of the many substances that can be falsely identified as ethyl alcohol by some breath machines.

Substances in the environment can also lead to false BAC readings. For example, an alcohol-free subject was asked to apply a pint of contact cement to a piece of plywood and then to apply a gallon of oil-base paint to a wall. The total activity lasted about an hour. Twenty minutes later the subject was tested on an Intoxilyzer, which registered a BAC of .12 percent. This level is 50% higher than a BAC of .08, which constitutes legal intoxication.

Any number of other products found in the environment can cause erroneous BAC results. These include compounds found in lacquers, paint removers, celluloid, gasoline, and cleaning fluids. Other common things that can cause false BAC levels are alcohol, blood or vomit in the subject's mouth, electrical interference from cell phones and police radios, tobacco smoke, dirt, and moisture.

Breath testers can be very sensitive to temperature and will give false readings if not adjusted or recalibrated to account for ambient or surrounding air temperatures. The temperature of the subject is also very important. Each one Fahrenheit degree of body temperature above normal will cause a substantial elevation (about 8%) in apparent BAC.

Many breath testing machines assume a 2,100-to-1 ratio in converting alcohol in the breath to estimates of alcohol in the blood. However, this ratio varies from 1,900 to 2,400 among people and also within a person over time. This variation also leads to false BAC readings.

Physical activity and hyperventilation can lower apparent BAC levels. One study found that the BAC readings of subjects decreased 11 to 14% after running up one flight of stairs and 22-25% after doing so twice. Another study found a 15% decrease in BAC readings after vigorous exercise or hyperventilation.

Some breath analysis machines assume a hematocrit (cell volume of blood) of 47%. However, hematocrit values range from 42 to 52% in men and from 37 to 47% in women. A person with a lower hematocrit will have a falsely high BAC reading.

Failure of law enforcement officers to use the devices properly or of administrators to have the machines properly maintained and re-calibrated as required are additional sources of error.

Research indicates that breath tests can vary at least 15% from actual blood alcohol concentration. An estimated 23% of individuals tested will have a BAC reading higher than their true BAC.

Principles of Chemical Testing

The "Breathalyzer" brand breath-testing device operates by using photocells to analyze the colour change of an oxidation-reduction reaction. A breath sample is bubbled through an aqueous solution of sulfuric acid, potassium dichromate, and silver nitrate. The acid acts as a catalyst, allowing the alcohol to be oxidized at an appreciable rate. In solution, ethanol reacts with the potassium dichromate, reducing the dichromate ion to the chromium (III) ion. This reduction results in a change of the solution's colour from red-orange to green. The reacted solution is compared to a vial of nonreacted solution by a photocell, which creates an electric current proportional to the degree of the colour change; this current moves the needle that indicates BAC.

Like other methods, the "Brethalyzer" chemical analysis is somewhat prone to false readings; compounds which have compositions similar to ethanol could also act as reducing agents, creating the necessary colour change to indicate increased BAC.

Myths

A common myth is that breath testers can be "fooled" (that is, made to generate estimates making one's blood alcohol content appear lower) by using certain substances. An episode of the Discovery Channel's MythBusters tested substances usually recommended in this practice -- including breath mints, mouthwash, and onion -- and found them to be ineffective. Adding an odor to mask the smell of alcohol might fool a person, but does not change the actual alcohol concentration in the body or on the breath.

References

• Hlastula, M. Physiological errors associated with alcohol breath tests . The Champion, 1985, 9,(6).
• Pariser, J. L. In vino Veritas: the truth about blood alcohol presumption in state drunk driving laws. New York Law Review, 1989, 64(1), 141-181.
• Peach, R. J. Who tests the DUI test? Defense can't; New Jersey won't let lawyers inspect new breath tests. The National Law Journal, 2000, 23(6), A4.
• Rosenblum. E. Breathlayzer machines are faulted once more. New Jersey Law Journal, 1988, 122(23), 5.
• Sargeant, G. Breathalyzer accuracy challenged. Trial, 1989, 25(12), 22.
• Taylor, L. Drunk Driving Defense. New York: Aspen Law and Business, 5th edition, 2000.

• Based on information in Alcohol: Problems and Solutions
• Breath Tester Accuracy