Types of Breath Testing Instruments
There are two primary types of instruments used for alcohol breath testing.
The most common type of breath test uses infrared spectroscopy in order to identify and measure the amount of alcohol in a suspects breath. Alcohol absorbs lights at specific wavelengths. Overly simplified, a beam of light is shined through a chamber containing air from the suspects lungs. A certain amount of that light is absorbed by the molecules of ethyl alcohol. The amount of light that reaches the sensor on the opposite side of the chamber is correlated to the amount of alcohol in the breath.
Electrochemical | Fuel Cell
The second most common type of breath test is an electrochemical test or “fuel cell” test. Essentially, when the ethyl alcohol on the suspects breath comes into contact with the fuel cell, it creates a chemical reaction called oxidation. As a result, the ethyl alcohol is broken down into acetic acid producing free electrons and hydrogen ions. The hydrogen ions travel to the lower surface of the fuel cell and form water. The end result is the top side of the surface having substantially more electrons than the lower side thereby creating an electrical charge between the top and lower sides. The strength of the electrical charge is used to determine the amount of alcohol found on an individuals breath.
Breath Testing is Not Accurate | Flaws and Assumptions
It does not matter whether your state uses an Intoxilyzer, which is infrared technology, or an EC/IR II, which is a combination of electrochemical and infrared, there are still substantial flaws in the ability of the machine to accurately determine a driver’s blood alcohol content. The following are just some of the flaws or issues with all breath testing equipment.
- Indirect Test – All breath tests measure the amount of alcohol in lung air in order to determine the amount of alcohol in the suspects blood. A direct test would be to test the blood to determine the amount of alcohol that is in the blood. Breath tests are indirect tests because a breath test substitutes breath for blood.
- It is illegal to drive with a BAC greater than .08. What this means is that it is illegal to drive with a Blood Alcohol Concentration of greater than .08%. In theory, the amount of alcohol in a suspects lung air does not matter. It is the BLOOD alcohol concentration that determines whether a crime has been committed. Accordingly, there must be a correlation between the amount of alcohol in lung air and blood alcohol concentrations.
- Partition Ratios – All breath tests ASSUME a 2100 to 1 partition ratio when converting a breath alcohol concentration into a blood alcohol concentration. The breath tests measure grams of alcohol for every 2100 parts air. This is directly proportionate to the amount of grams of alcohol in every milliliter of blood. The assumed partition ratio of 2100 to 1 is simply used as it is easy to calculate because the quantitative values are equal. The assumed partition ration is not accurate and the air to alcohol partition ration varies from 1,300 – 1 to 3,100 to 1.
- In order to determine how the partition ratio effects the outcome of the breath test can be done with a simple calculation. Take the new presumed partition ration and divide by 2,100. For example, an individual with a 1,500 to 1 partition ration would have approximately a .07 BAC. However, the machine would read a .10. Step 1: Divide the new partition ration, 1,500 by the standard partition ratio. 1500/2100 = .714. Step 2: Move decimal 1 spot to left. .714 becomes .0714. Accordingly, the .0714 is the suspects real BAC, but the machine will read a .10. An extreme example is an individual who has a 1,300 to 1 partition ratio. 1300/2100 = .691. Move the decimal one spot to the left and the suspects true BAC is .069. However, the machine will read a .10.
- A suspect’s partition ratio may very well seal his or her fate. A .069 BAC is legal in most, if not all, states for individuals of legal age to drink. However, with a partition ratio of 1,300 to 1, the breath test will read .10 which is guilty in all states.