Police Breathalyzer Accuracy Issues | Charlotte DWI Attorneys

Don’t Assume Police Breathalyzer Accuracy

The Theory of Breath Testing

Police breathalyzer accuracy is a hotly contested subject. Here is why we do not buy the manufacturer’s claims. Consumed alcohol can be theoretically tested from breath samples because it eventually is absorbed into a person’s bloodstream through the mouth, throat, stomach and intestines. Alcohol is neither digested nor chemically altered during the transition process into the blood. Then, as the blood circulates through the lungs, a physiologically “predictable” amount of the consumed alcohol will migrate across the lung membranes and into the lungs themselves. Once mixed with air in the lungs, it evaporates, is exhaled, and can then be measured. Of sorts. At least in theory, the concentration of alcohol in the subject’s expired breath should correlate with the concentration of alcohol in their blood.

police breathalyzer accuracyFirst, breathalyzers only “estimate” the blood alcohol concentration (BAC) indirectly. They do not physically measure it. That would require the analysis of an actual blood sample. And, different machines utilize different techniques and different types of technology. The only true measure of blood alcohol is analysis of a person’s blood. And even then, this does not automatically mean they are guilty of impaired or “drunk driving” unless the sample is taken at the time of police stop on the side of the road. If the sample is collected some time later back at the police station or at a medical facility, the BAC level will have changed.

Detection of Other Chemical Structures

One major concern with certain machines is that they may identify the ethyl alcohol (or ethanol) found in alcohol beverages as well as other substances with similar molecular structures. For example, some police breathalyzer machines still quantify and calculate all compounds containing the methyl group structure. At any given time, there can be over one hundred compounds found in the human breath, and up to 70 to 80 percent of them may contain the methyl group structure. Research conducted by the National Highway Traffic Safety Administration (NHTSA) has concluded that certain dieters and persons with diabetes can have sharply elevated acetone levels, perhaps hundreds and even thousand of times higher than normal. Acetone is just one of many substances that can be falsely identified as ethyl alcohol in breath testing equipment.

Substances in the environment can also lead to falsely high BAC readings. Painters and others who work with strong chemicals can be charged with a DUI after leaving work for home. Additionally, there bodies may harbor certain chemicals for hours or even days after working around them. For example, studies have shown that a painter even while wearing a protective mask can result in an Intoxilyzer BAC reading of .075% after spray painting a room for 20 minutes. Other products found in the environment that can cause erroneous BAC results include compounds found in lacquers, paint removers, celluloid, gasoline, and cleaning fluids.

Partition Ratio (best guess formula)

Most breath testing machines are programmed to use a standard 2,100-to-1 ratio in converting alcohol in the breath to estimates of alcohol in the blood. The ratio of breath alcohol to blood alcohol is called the “partition ratio” and reflects that the alcohol content of 2100 milliliters of exhaled air should be the same as for 1 milliliter of blood. The problem is that each individual is different.

Physiologically, this partition ratio can vary between 1700 and 2400 depending upon the individual and can even vary within the same person over time. Such natural variation can result to a breath analysis reporting either a higher or lower calculated blood alcohol reading. The prosecution will defend this variation by stating the 2100:1 ratio is a scientific norm. But again, this admission highlights the inherently speculative nature of breath testing in general.

Temperature of Testing Room

Breathalyzers are very sensitive to temperature which can cause false readings if not properly adjusted to account for ambient or surrounding air temperatures. For example, if a breathalyzer is situated near an open door to the outside, temperature variations could affect BAC results.

Body Temperature of Test Subject

The partition ratio of 2100:1 is based on a normal body temperature of 98.6°F. A higher body temperature of the test subject will overestimate the actual BAC because alcohol vaporizes more rapidly into the body as it is warmed. Thus, an elevation in body temperature of 1°C (1.8°F) can result in a 7% higher value in the result since air in the lungs would contain an artificially higher amount of evaporated alcohol. As a result, someone with a cold or flu will test significantly higher than someone without a fever.

Cellular Composition of Test Subject’s Blood

Whole blood is actually made up of suspended cells (e.g. red and white cells) as well as certain proteins. As we all know, it is only a partial liquid and separates into serum as it clots. The partition ratio of 2100:1 is factored on an “average cell volume” of 47% (known as the hematocrit level). However, as with the 2100:1 ratio, hematocrit values will also vary in individuals and can range from 42 to 52% in men and from 37 to 47% in women.

Someone with a lower hematocrit will be given a falsely high BAC reading. As a result of these and other factors, research has found that breath tests can vary at least 15% from actual blood alcohol concentration. And, approximately 23% (that’s about one out of every four) of all individuals tested will have a BAC reading higher than their actual blood alcohol in their system.

Other Factors That Can Affect Breathalyzer Accuracy

  • Breathalyzers presume that the breath sample being tested comes from deep in the subject’s lungs. However, this is not always the case. Most persons being tested are quite anxious and tend to breathe shallowly. This accounts for the number of times some individuals are required to be tested in order to provide a sufficient sample. Other persons may suffer from asthma or other breathing conditions which can limit their ability to provide a deep breath sample.
  • Breath alcohol concentration can also be artificially increased by vomit or blood in the mouth, acid reflux, or having had a drink right before the time of testing. Mouthwash or breath freshener will also often contain alcohol and inflate BAC readings.
  • Electrical interference from cell phones and police radios can result in different readings.
  • Absorption of alcohol into the blood may be delayed by as much as 1-2 hours after consumption. So even though you may have a “strong odor of alcohol” on your breath, it takes time to be absorbed, and therefore, cannot affect your ability to drive a vehicle. Significant time delays between police stop and breath testing should always be considered by your DUI attorney.
  • Every breathalyzer is a machine. And every machine is subject to fail over time and has a “margin of error.” Police and prosecutors prefer the term “instrument” as opposed to “machine.” When questioned further, most officers reply that this is the term taught during breathalyzer training. The retort is that the term “instrument” implies a more “scientific” device, and hence, makes it more reliable. But in the end, what it is called doesn’t matter, and a machine is still subject to error.

If you have been arrested and charged with a Charlotte DUI and have a BAC level of 0.08% to 0.10%, these relatively minor variations in readings and other factors affecting police breathalyzer accuracy could make a real difference at trial. Better make sure your DWI attorney is proficient at explaining and then challenging breath test “science” before deciding which law firm to retain. Little facts oftentimes make a big difference in DUI cases. Leave no stone unturned.