How Does Alcohol Breathing Test Work in The UK?

We often hear about accidents on the news, and they often mention how police caught an individual drunk driving. Alcohol intoxication makes you lose your senses, so even if it is illegal to drink and drive an intoxicated individual might dismiss such laws. Eventually the person must sober up and face up to their actions. Drivers who are caught drunk driving are charged with a felony. 

police car stopping a driver

But how does the police or any individual finds out if someone is drunk? This is where a alcohol breathing test come in handy. They measure the Blood Alcohol Content (BAC) to ascertain whether an individual is drunk or not. There are also vitamin level tests. Why not check out our article.

What Is Blood Alcohol Content (BAC)?

To understand how alcohol tests work, we need to know how our body absorbs the consumed alcohol.

When you consume alcohol, it goes into your stomach, and from there, your bloodstream absorbs it. This blood travels to your brain and lungs. And from your lungs, you breathe it out. So when you exhale the air, it has the alcohol content in it. 

The alcohol breathing test determines the level of alcohol in the air you blow out. The device uses this amount to evaluate the alcohol content in your blood. This measurement is called the Blood Alcohol Content (BAC).  

BAC is generally highest approximately 1 hour after drinking. However, it goes up after 15 minutes of downing alcohol. 

What Does The Device Contain?

The device contains:

  • A slot to take in the breath
  • Two glass containers for the chemical mixtures
  • A meter that determines the colour shift after the chemical reaction to give us the BAC 

How Does The Test Work?

Now let us look into the science behind how this test works to give us the BAC. 

The system starts with the individual breathing into the device—the sample bubbles through the mixture of silver nitrate, potassium chloride, water, and sulfuric acid.

The principle behind the entire system focuses on these two chemical reactions: 

  1. The sulfuric acid helps remove the alcohol from the air and into a liquid solution 
  2. The potassium dichromate reacts with the alcohol to create chromium sulfate potassium sulfate acetic acid water

On the other hand, the silver nitrate does not take part in the reaction. However, it is a catalyst that makes the reaction go faster. The sulfuric acid provides the acidic ecosystem needed for this reaction and eliminates the alcohol from the air. 

We know it sounds too complicated, but we promise this is the last bit. The orange dichromate ion responds to alcohol during the entire chemical reaction, and it changes color to a green chromium ion. The amount of the color change is proportional to the occurrence of alcohol in the breath. 

Next, the reacted mixture is compared to an unreacted mix in the photocell system. Finally, it generates an electric current that sparks the needle on the meter to move. The operator then needs to turn the dial to bring the needle to its initial place and read the level of alcohol from the knob. 

man using breathalyser

How Precise Are Alcohol Breathing Tests?

There are very slight chances of alcohol tests producing wrong results. Even though they are mostly accurate, they are still not perfect. Much like any other device, there is a margin of error. The alcohol breathing tests can be off as much as 0.01 BAC. 


Alcohol breathing tests help individuals and organizations to know when an individual is high on alcohol. It can assist people in keeping a check on their drinking habits, while institutes such as the police can keep a check on alcohol-induced crimes. 

bottles of alcohol in a bar