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How to Ensure Breathalyser Accuracy.

breathalyzer_licensedAlcohol impaired drivers risk not only their own lives but the lives of others. They can face large fines, loss of license and even imprisonment. By removing these drivers, we reduce the potential for serious injury or fatal collisions on our roads.

But how do we do that?

Most people, at one point or another, have been stopped for a Random Breath Test (RBT). Drivers may randomly be stopped by Highway Patrol and signalled to pull over for an RBT (Random Breath Test).

The officer will advise you have been pulled over for the RBT, request you to pull out your driver’s licence, and asked if you have consumed any alcohol that night. This Random Breath Test is as simple as talking close to an alcohol breath testing device (Passive Test) or by blowing into a straw (Active Test). Active units are slightly less prone to environmental contamination. A Breathalyser is a Breath Alcohol Device which measures a person’s BrAC (Breath Alcohol Concentration).

In Australia our driving limit is 0.05. Should your test result in a reading higher than this you will need to take another test back at the police station with an Evidentiary Breathalyser. The results of this breath test can and will be used in a court of law.

How do we know that these breath alcohol devices used by the RBT, Highway Patrol or any Law Enforcement are correct?

Service and calibration is now part of new AS3547:2019. This is very important as regular breathalyser calibration maintains the instrument’s accuracy. A breathalyser reads the alcohol content in your breath, and, similar to other gas detection instruments, over time the breathalyser looses its accuracy in reading.  A known reference material, ethanol (cylinder gas or liquid solution) which mimics alcohol on person’s breath, is used for the calibration of breathalysers. Calibration should be done by a trained professional, as per manufacturer’s recommendation, usually every six months.


There are two methods used for calibration of Breathalysers. Ethanol cylinder gas and Ethanol liquid solution.

Ethanol cylinder gas is used as a known substance in various concentrates, as per the manufacturer’s recommendation, to calibrate the breathalyser. This is used alongside the manufacturer’s software which checks the instrument for software updates, clears data errors and, generally, makes sure everything is working as it should.

Liquid Ethanol solution also comes in various strengths and purities. It can be bought pure and mixed onsite or premixed. This certified alcohol solution is heated to 34°C, then connected to a pressurised flow meter attached to an air generator to provide an accurate air sample. The breathalyser is told to recognise the sample at the level of alcohol within it.

Both methods have their positives and negatives. Ethanol cylinder gas has a shelf life of 36 months where the Ethanol liquid solution expires quickly in around 6 months.

There are many different types of breathalysers on the market. Fuel cell breathalysers offer the highest level of accuracy. These require a shorter start up time and offer readings up to 3 decimal places. These breathalysers can remain accurate between calibrations for thousands of test and hold calibration longer than semiconductors.

Semiconductor sensor technology is generally cheaper than fuel cell sensor technology. These are good affordable option for personal use but are slower and show a wider variation in readings. Most semiconductor breathalysers only show up to 2 decimal places and require calibration more often. They can also give false positive readings even when alcohol is not present, caused by substances like ketones; cigarette fumes; diabetics’ breath; even hair sprays and mouthwashes. For better accuracy, invest in a fuel cell breathalyser instead for personal or workplace use.


Ethanol – C2H6O – is a volatile, flammable, colourless liquid with a slight characteristic odour. It is the primary ingredient found in alcoholic drinks. It burns with a smokeless blue flame that is not always visible in normal light.

CAC Gas and Instrumentation supplies ISO17025 accredited ethanol cylinder gas in various cylinder sizes including 34L and 103L non-refillable cylinders with C10 Valves. If larger volumes of gas are required, ethanol also comes in high pressure cylinders.

Our ISO 17025 gases are manufactured to the highest quality, traceability and reliability. CAC stocks ethanol mixtures in both Sydney and Singapore.

Breath Alcohol Testing Brochure

For more information view or download our 
Calibration for Breath Alcohol Testing Brochure


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