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Legal Drink Drive Limit: How To Test Yourself

19 Oct 2012 at 13:08

If you’re going out for a drink, the sensible option is to leave your car at home. Alcohol and driving do not mix: it’s as simple as that.

But sometimes you might be out for the evening, circumstances change and the night needs to be curtailed. Likewise, the human body processes alcohol at different rates, meaning the morning after the (heavy) night before could see you still unfit to drive.

So is there any way to tell whether you are safe to climb back behind the wheel? Put simply, yes.

Come March next year if you travel in France without a personal breathalyser in your car you’ll be liable to an €11 fine (blog post - Half of motorists risks fines in France). While it’s not law to carry one in the UK – and not looking like the government will introduce legislation anytime soon – these kits are still useful.

There are many different types:

Sensor type

Although more sophisticated than your standard off-the-shelf items, this type of machine uses similar technology to the machines the police use in the UK. These types of breathalyser use a sensor to determine your blood alcohol level.

As the breath hits the sensor, the computer picks up the concentration of intoxicants in the gas and applies a formula to the reading to work out blood alcohol level.

All breathalysers require a sample of breath to test for the presence of alcohol, however, of the sensor-based machines there are two types available. Mouthpiece (active) and blow-over (passive) differ in that the mouthpiece type uses a sealed tube to direct your breath into the system.

This is generally more accurate than the blow-over, which can be contaminated with air from the atmosphere, possibly throwing a reading out.

Colour indicator type

These systems rely on you breathing into a bag through a tube filled with reactive crystals. Subjects are required to inflate the bag then compress the filled chamber to push their breath back through the crystals. If alcohol is present, the minerals change colour to notify you.

Your blood alcohol level can be cleverly determined from your breath. As you drink alcohol and it is absorbed into your blood stream, this blood then passes through the lungs to become re-oxygenated, with a certain amount of alcohol evaporating off in the respiratory organ.

This is then exhaled as part of your breath where a breathalyser can pick up the percentage of intoxicants.

Around 50% of drivers admit they’d drive the morning after having a drink but often many are not fit to pilot a car.

The UK has a lax attitude when it comes to drink-driving – arguably exemplified by the comparatively high blood alcohol limit (blog post - Is our drink drive limit too high) – and personal breathalysers are not particularly prevalent.

It needs changing on the grounds of safety. Maybe a new law, like in France, is the only way to get the ball rolling?