We used a breathalyser to test how our weight affected our alcohol tolerance - some of the results surprised us

Wednesday, 21st March 2018, 8:48 am
Updated Wednesday, 21st March 2018, 10:45 am

How much can you drink before you're over the drink-drive limit? The rule of thumb - I was always told - is that a pint and a half of beer would see you touching the legal margin.

When the Scottish Government changed the limit in Scotland to 50 milligrams of alcohol for every 100 millilitres of blood - 30 milligrams less than the limit in England, Wales and Northern Ireland - many Scots adjusted that rule of thumb to a single pint, or a bottle.

Wherever you live though, the problem with rules of thumb, is that everybody's thumb is a different size.

At the office we decided to put our tolerances to test (in the name of public safety) and set up an experiment to demonstrate how people are affected differently by alcohol - and at different rates.

For the sake of the test our team of four - ranging from mid-twenties to late, late forties, from five feet seven to six feet five and from 62.5 kilograms to 96 kilograms - all drank the same alcohol, with the same mixer. We breathalysed ourselves at a suitable gap between each drink and took note of the results.

The drink: Cockspur Fine Rum, ABV 37.5%The mixer: Diet CokeEquipment: 4 plastic tumblers, one 25ml optic measure, one professional-grade breathalyser

The results

After two single rum and diet cokes and one 25ml shot of straight rum each, some of the results of our test were predictable:

Everyone felt a bit wobbly after nipping into a meeting room and drinking rum for an hourThe tallest and heaviest member of the team consistently registered the lowest readings on each test - showing a blood alcohol level of 0.19 milligrams after three drinks.The shortest and lightest member of the team - and the only female in the test group - had the highest reading after three drinks.

Some of the results were more of a surprise:

At the end of the test, the second heaviest member of the group (76kg, 0.46mg) registered a significantly higher reading than the second lightest (67kg, 0.40mg). This was also true of the penultimate reading.The person who finished the test with the highest reading (0.75mg) actually had the second lowest reading after one drink.And, most surprisingly, after three single-measure drinks all four of us were still reading as legal to drive in England, Wales or Northern Ireland thirty minutes after our final drink.

So did any of us feel like we could safely drive?

No. All of us felt like our driving ability would be compromised, even though only one of us registered over the Scottish drink drive limit and all of us would have passed a roadside test anywhere else in Britain.

But that doesn't tell the full story. Our final test was conducted about 30 minutes after our final drink but it can take anything between 30 minutes and two hours for alcohol to fully absorb into a person's bloodstream, meaning, despite our 'legal' readings, that some of our readings may have risen further had we tested ourselves later on in the evening.

And the readings that surprised us? It turns out, they shouldn't have. The list of variables on the NHS Choices website that could affect a drinker's blood alcohol content are numerous. Whether you are male or female (a man's body has higher water content than a woman's meaning men are better able to dilute alcohol), your age, your weight, what you have eaten and how recently (a full stomach will slow the rate your body absorbs alcohol - but not prevent it happening), the type of alcohol you have been drinking and your stress levels all have an impact on how drunk you get - and how fast.

The NHS advice on alcohol and its effect on driving couldn't be clearer: "The safest option is not to drink any alcohol at all if you plan to drive. Even a small amount of alcohol can affect your ability to drive, and there's no safe way to tell whether you're within the legal limit."

That's a view echoed by Hunter Abbott, MD of Alcosense - who manufacture the breathalyser we used in our experiment - and member of the Parliamentary Advisory Council for Transport Safety: “Whether you’re Joe Bloggs or Lewis Hamilton, it’s in the evening or the morning after, any alcohol affects your ability to drive and therefore safest when you’re at zero.”

Mr Abbott is calling for a lower limit across the UK to reduce the amount of drink drive-related accidents.

"A study of 4,000 drink drive accidents showed that at the English limit you are 13 times more likely to involved in a fatal accident than when sober, at the Scottish limit you are still five times as likely,” he points out.

“At AlcoSense we very much support lowering the English limit to match that in Scotland, or preferably lowering even further."

After three drinks and a reading putting most of us (just) under the strictest of the UK's drink drive limits - cheers to that.

Our test was conducted using a £249.99, professional-grade AlcoSense Ultra breathalyser which uses the same 200mm2 fuel alcohol sensor found in UK, US and European police breathalysers. The AlcoSense range starts at £2.99 for a single-use test.

All of the participants in this test returned home from work using public transport.