How to use a breathalyzer

Thursday, October 13, 2022

How alcohol is processed

When you drink, alcohol is absorbed into the blood stream through your mouth and throat but mostly through the stomach and small intestine. The more you drink, the more alcohol is absorbed by the body and the higher your blood and breath alcohol readings will become.

Around 90 minutes after your last drink the alcohol is distributed equally around the body and through the blood stream. About 90% of the alcohol is broken down into water and carbon dioxide by the liver in a process called oxidation. The remaining 10% of the alcohol continues to the lungs and kidneys.

How to choose the best breathalyzer

A healthy liver typically breaks down alcohol at a rate of one unit of alcohol per hour but sometimes it can take a longer or shorter time. When you stop drinking your level of intoxication can change quickly (rise or fall) for up to 90 minutes afterwards because of the time it takes for alcohol to reach the bloodstream after drinking. For example it will take longer for alcohol to reach the bloodstream if you have eaten recently, less time on an empty stomach. There are many factors that can influence the reading just after drinking. This is the reason not to use breathalyzers within 90 minutes of drinking.

How to read a breathalyzer UK

Do read the manufacturer’s instructions carefully, as they will tell you how to read breathalyzer test results. Certain medications and conditions including diabetes can give false positive readings. Leave a minimum of three minutes between tests and do not perform more than 10 tests in one hour. More frequent testing can cause a build-up of breath condensation in the breathalyzer which can temporarily affect accuracy. Don't blow into the breathalyzer within 10 minutes of drinking. High levels of alcohol in the mouth can permanently damage the sensor. And don’t carry out a breath test within 90 minutes of drinking. Blood alcohol levels can rise for up to an hour and a half after drinking. Don’t use the breathalyzer for at least 30 minutes after using mouthwash, breath spray, cough medicine or after smoking a cigarette or eating ripe fruit - you may get a false positive from your breathalyzer readings. Don’t perform a test in dirty air, for example a smoky room or pub. And don’t use the breathalyzer if you are breathing quickly (for example, after running up the stairs).

Breathalyzer use when driving abroad

If you are using a breathalyzer abroad, you may need to change the Blood Breath Ratio (BBR) setting as well as the drink drive limit. The BBR is the ratio that is used to convert a breath alcohol reading (displayed in mg/L) into a blood alcohol reading (displayed in ‰BAC).

Breathalyzer calibration

To ensure continued accuracy, all semi-conductor and fuel-cell breathalyzers (ie. excluding single-use) require periodic re-calibration. It’s rather like your car needing an annual service. Over time, a breathalyzer may change the way it responds to alcohol and the results may become less accurate (drift). It is recommended for optimum breathalyzer use that they’re re-calibrated every 12 months by the manufacturer.

FAQ

I can’t get breathalyzer test results

This may be because you’re blowing too hard, too soft or not for long enough into the mouthpiece. Try blowing like you're taking a sigh. If you’re running out of breath before the result is shown, reduce the pressure of your breath slightly

I've done two breath tests and got different breathalyzer readings

This is expected for several reasons. The first test is the most accurate. If you perform a second test within a few minutes of the first, the alcohol levels in your lungs may not have stabilized – causing the second test to give you a different reading. If you’ve recently drunk alcohol, your blood alcohol level can also change quickly over the course of a few minutes. UK law allows for a 15% difference in sequential readings as a result. Therefore you should only use a personal breathalyzer at least 90 minutes after drinking or ideally, the morning after.

My unit says Saturation Lockdown (or similar)

This is caused by blowing in an abnormally high level of alcohol. It is normally caused by doing a breath test just after sipping an alcoholic drink and there is residual alcohol left in the mouth. This overloads the sensor and can make it read inaccurately whilst the sensor recovers. Wait a while before trying again.

My unit says “Calibration Expired” or “Calibration Due”

After about 12 months, readings may become unreliable. Contact the manufacturer to arrange recalibration of the unit.

I’ve done several quick tests in succession and my breathalyzer scores are different

This may be caused by a build-up of breath condensation in the breathalyzer which can result in temporary inaccuracy until it evaporates. To avoid this, leave a minimum of three minutes between tests and do not perform more than 10 tests in one hour, and no more than 30 tests in 24 hours. Always use a new mouthpiece for each test. If you do experience this problem the condensation should evaporate within 2 hours at normal room temperature and the breathalyzer will return to normal operation.

My breathalyzer started to do a test by itself and displayed an error

This can happen if the breathalyzer is used in a noisy environment over 95 decibels. If the unit is one that needs to be slid open to start the test, pressure changes because of loud noises can occasionally cause the unit to think breath is now entering the device, and then show a blow error. If this occurs, move to a quieter area away from the source of the sound and attempt the test again.

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