In this blog post, we will look at how drunk driving is detected scientifically through the working principle of breathalyzers and the chemical reactions used to detect alcohol.
In our busy lives, who hasn’t washed away their worries with a drink? For modern people living increasingly busy lives, alcohol seems to be an inseparable part of life. However, behind its powerful appeal lies the dangerous reality of drunk driving. Drunk driving is considered a potential risk of murder, and even many politicians and celebrities are not exempt from being caught drunk driving. In many cases, they deny that they have been drinking, but a palm-sized breathalyzer can always suspend or revoke your driver’s license. So how does this breathalyzer work?
The answer is the oxidation-reduction reaction of alcohol. When a person who has been drinking breathes into a breathalyzer, the alcohol contained in the breath is oxidized inside the device, reducing the orange potassium dichromate (K2Cr2O7) in the device to green chromium trioxide (Cr2(SO4)3). The police officer only needs to check that the color of the device has changed. A detailed explanation of this process is as follows.
It is well known that ethanol is the main component of alcohol. Ethanol is a substance that exists in the form of an ethyl group (C2H5-) with two carbon atoms and a hydroxyl group (-OH) attached (C2H5 + OH = C2H5OH). When ethanol is consumed, it suppresses the central nervous system, causing drowsiness, excitement, and dizziness, while at the same time stimulating the brain to produce endorphins, which make people feel good. It is because of these effects that alcohol has been used as a staple beverage throughout human history.
Alcohol, including ethanol, has several common characteristics due to its hydroxyl group, one of which is the redox reaction mentioned above. Oxidation refers to the process in which atoms that like electrons, such as oxygen and halogens (elements in group 17 of the periodic table), are added to a molecule, or atoms that dislike electrons, such as hydrogen, are removed from a molecule. Reduction is the opposite process, which occurs simultaneously with oxidation, as briefly explained in the blood alcohol measurement process above. In the case of ethanol, it is oxidized under certain conditions to form a substance called acetaldehyde, which is then oxidized once more to form a substance called acetic acid.
Of course, for ethanol to oxidize in this way, a reducing agent (potassium dichromate) must be present. Chromium (Cr), with atomic number 24, appears orange when present as Cr(VI), a highly oxidized state within compounds. Interestingly, when reduced to Cr(III), it turns dark green. Chromium can form various compounds, and among them, chromium in potassium dichromate is orange Cr(VI). This potassium dichromate is attached to silica gel and contained in the tube of a breathalyzer in powder form. When a driver blows into the tube, the ethanol contained in their breath causes the following reaction.
2K2Cr2O7 (orange) + 8H2SO4 + 3C2H5OH (ethanol) → 2Cr2(SO4)3 (green) + 2K2SO4 + 11H2O + 3CH3COOH (acetic acid)
As can be seen from the above reaction, ethanol is oxidized and converted to acetic acid, and orange potassium dichromate is converted to green chromic acid. As a result, the color inside the breathalyzer tube gradually changes from orange to green and spreads. This visual result indicates that the driver’s breath contains ethanol. About 10% of the alcohol we drink is not digested and is absorbed into the bloodstream and spreads throughout the body, and alcohol is contained in the breath at a ratio of 1/2100 of the blood alcohol concentration (i.e., the amount of alcohol in 1 ml of blood is equal to the amount of alcohol in 2100 ml of exhaled air). Breathalyzers calculate blood alcohol concentration based on this ratio. If more than half of the measuring tube turns green, it means that the driver’s blood alcohol concentration is 0.08% or higher, which is the legal limit for drunk driving in Korea, making it possible to measure alcohol consumption in this way.
As shown above, breathalyzer tests can be performed simply by blowing into the device, and drivers who are determined to be drunk driving through this test undergo a blood test to obtain more accurate readings. Gas chromatography can be used to separate blood and filter out alcohol and other volatile substances, allowing for accurate measurement of blood alcohol concentration. Fines and prison terms are determined based on the readings obtained.
Recently, a new drunk driving prevention technology being developed by the National Highway Traffic Safety Administration (NHTSA) has been the subject of much discussion. Called DADSS, this technology uses a system installed in the car to detect alcohol in the driver’s breath or on the driver’s fingertips when they touch the car to start the engine. Once this technology is fully developed, there are plans to make its installation mandatory in all new cars manufactured in the United States. As you can see, technology to prevent drunk driving, which can be considered a potential act of murder, is advancing day by day. These measurements, which use chemical reactions and spectroscopic methods, cannot be avoided by smoking, drinking coffee, or eating garlic just before a drunk driving check. Everyone has moments when they want to wash away their worries with a drink, but wise people know that it is best to avoid drunk driving at all costs.
