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How Alcohol Breath Test Works: The Science Behind Drug Testing

Drug testing has become common these days, especially in workplaces. Different tests to determine the use of alcohol, marijuana, cocaine, and other substances are conducted to evaluate the history of drug use of the employee. Not just employers, competitive sports, prison parole programs, and several law enforcement agencies, in general, require drug tests mandatorily for different purposes.

A breath test to determine alcohol consumption levels is one of the most common and frequently used tests today. You may have seen the analyzer machine carried by law enforcement officers to test drivers’ blood alcohol content. The test is a quick way of evaluating the individual’s alcohol consumption within the past few hours. Let us understand the science behind the breath analyzers in detail to know how it evaluates the blood alcohol levels.

Why Test Alcohol Levels?

An increase in blood alcohol level leads to inhibitions in decision-making that can have lethal consequences. It could make your motor skills respond slowly, thus increasing risks while operating a vehicle or heavy machinery.

A breathalyzer test typically checks the alcohol concentration level in the air that you exhale. For most countries, the BAC level should be within 0.08 percent for a legal-aged driver during the test. Anything above these levels is considered as driving under intoxication and will therefore be prosecuted for the same.

But how does the tiny device you blow air determine the alcohol level?


The Journey of Alcohol

From the time you enjoy sips of your favorite spirit to the time it leaves your system, the alcohol goes through several processes that influence the breath test results. The alcohol you drink moves down the throat to enter the stomach, going through absorption into the bloodstream. As the stream is already exposed to the oxygen absorbed from the lungs, this oxygenated blood will carry the alcohol from your stomach to all the organs, including the lungs and brain.


Once the blood reaches the lungs, it gets through tiny air sacs, also known as alveoli, useful for exhaling the carbon dioxide from the body. In this case, the blood also carries alcohol, which transfers from it into the air you exhale. The entire process of blood’s exposure to alcohol could occur anywhere within 15 – 30 minutes of consumption and remain in the stream for up to two to three hours.


BAC – Breath Alcohol Content

There are two most common types of tests- the electronic and the manual. An electronic breathalyzer test device consists of a cathode or positively energized electrode and an anode or a negatively energized membrane.

The ethanol that saturates the air you exhale interacts with the environmental moisture at the anode. This process leads to the oxidation of alcohol bonds of ethanol to form OOH bonds or acetic acid. At the cathode, the moisture from air converts into water. Given the two processes are linked, the electrical charge at the two poles is influenced by the alcohol quantity in your breath or alcohol concentration. Hence, based on the charge, the device relates it to how much alcohol is present in your breath and gives the result.

Manual test setups typically consist of a balloon and a hollow cylindrical chamber containing yellow granules. You will inflate the balloon, and the air containing alcohol will travel to the chamber. Depending on the alcohol concentration in your system, the granules will switch colors from yellow to green. The number of green bands determines the concentration range of alcohol. One green band represents less than 0.05 percent, which is legally allowed. Two bands represent 0.05 – 0.1, and three represents 0.1 and above, both of which are not safe limits for driving.

Factors Influencing BAC

Lots of factors influence your blood alcohol concentration. It is essential to keep them in mind to ensure your testing levels fall within the acceptable range.


BMI or body mass index has an effect on your BAC. Individuals with more water in the body tend to be heavier. But the advantage here is that the water will dilute the alcohol level to get a low reading.


The food you eat with alcohol influences the reading. When you drink on a full stomach, the body takes longer to process the alcohol, thus reflecting on higher readings. It is mainly a problem if you have protein-rich meals.


How much and how quickly you drink also increases the chances of getting a high BAC. If you drink too much alcohol quickly, the body will take time to process the alcohol, thus increasing its concentration in your breath.


Men and women naturally have different capacities for alcohol. Men tend to have more stomach acid that enables faster and more efficient breaking down of alcohol. Thus, their chances of showing high BAC is comparatively less than that of women. Apart from this, hormone fluctuations also affect the alcohol levels in your system significantly.


What About the Breath Test Accuracy?

Breathalyzer tests typically show accurate assessments. The evaluator would take an average of many readings to get the best results. But that said, several factors influence the concentration levels. For example, alcohol traces from a short duration of consumption before the test can cause higher concentrations. Similarly, using mouthwash or fresheners with alcohol or even smoking can impact the results.

The electronic device could also suffer from bugs or low battery during evaluation that could influence the concentration. Therefore, breath alcohol tests followed by blood and urine tests are more reliable testing methods.



A breath test is one of the most common ways of rapidly determining blood alcohol levels. The typical scanning window for the alcohol test is within 2-3 hours of consumption and is therefore used as a basic diagnostic test. The science behind these analyzers ensures that there is competent accuracy of evaluation in most cases.

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