Patterson Law’s “Scientific Experiment” in relation to over-the-counter breathalyser devices

Parliament is debating reducing the legal drink drive limit so that it falls in line with European levels. The new proposed limit will be 22 µg in breath. At the moment the legal limit is 35 µg.

We thought it would be helpful to conduct a light-hearted breath test experiment.

We wanted to test some of the common theories relating to alcohol consumption and how it affects people with the added bonus of having to drink alcohol loosely in the interests of science!

A number of things could be assessed in one entertaining experiment:

  • How quickly people of different heights and weights got drunk
  • Whether reaction speeds worsened the more we had to drink
  • How much alcohol the staff of Patterson Law could drink before they reached the limit. This being measured using shop bought breathalysers
  • Whether breathalysers that are readily available for anyone to buy online seem to be accurate

After rounding up a number of participants and drafting a handy chart to record the results we went to one of our local drinking establishments.

The rules were simple:

3 of the group would drink 175ml of wine each round (2.1 units at 12%)


4 of the group would drink one pint of lager/beer (2.8 units at 5%)

Roughly 20 minutes after finishing each drink we would blow into a breathalyser (breathalyzer) and measure our breath alcohol level. To ensure this was accurate and to avoid cross contamination each person had their own mouth piece, apart from two people who had to use chunks of plastic drink straw in the device.

To assess the reaction speed, after every drink each participant would test themselves using the human benchmark test. A simple reaction test that required someone to press a button when a light changed from red to green, so simple even we couldn’t mess it up.

The Breathalyser Test

After one drink each we had the first revelation of the evening. We allowed a patron of the pub to test himself using one of the devices. He had been drinking at the pub for 5 hours and had consumed 3 pints of cider and 7 bottles of carling, his breath reading was 40ug.

If a person is arrested and breathalysed at the station and gives a reading of less than 40 µg they are released without charge. Had this man have been arrested he would have probably metabolised sufficient alcohol on route to the station to have avoided charge. He appeared to be heavily inebriated. Due to this seemingly anomalous reading, this particular device was deemed to be inaccurate and was cast aside.

We don’t want to name the devices in question because we don’t want to be sued. There is a small chance we were not using it properly. But that begs the question as to whether or not somebody who was inebriated would be able to use the device properly in order to get a reliable reading. At this stage we’d only had half a drink each.

Breathalyser Test Results & Accuracy

After 3/4 rounds of drinking the results appeared to be inaccurate and inconclusive. There was absolutely no correlation between reaction speeds and alcohol consumed, some people testing better after 3 pints then they did at the beginning. The breath test results were even worse. A 6ft 7” male reached the drink drive limit quicker than a woman half his size according to the device.

After assessing the results it seemed evident that only two things were conclusive from our experiment.

1) You will not be able to drink as much and then drive with the proposed new drink drive limit (obviously). As most people within the group reached the 20 mg threshold after their first drink. See the chart;

handheld breathalizer results

2) Store bought breathalysers are either completely unreliable or a bunch of lawyers aren’t capable of using them properly despite reading the instructions beforehand.

For example in relation to Daniel Park (who is 6 foot seven) was over the legal limit after 2 pints yet after another pint (half an hour later) he tested as under the legal limit. (The chart shows just how confusing the results were).

graph showing over the counter breathalyser testing

After reviewing the results of our test, which while not being conducted under laboratory conditions, were conducted under real life conditions, similar to how the devices are intended to be used. We can draw several conclusions;

1. Either a group of highly educated motoring solicitors are not capable of using a hand held over the counter breathalyser correctly, or;

2. The devices are not accurate enough to be able to provide the information a driver would need before possibly driving.

3. All of our testers would have been in excess of the proposed drink drive limit of 22 µg in breath after their first drink.

Based on our testing, it would be a brave decision to rely on the test results from these devices before driving, and the best advice is always to drink nothing if you intend to drive afterwards.

In the near future we are going to get a pharmacologist to come and see us with a proper lion intoxilyser machine. Watch this space and we will report our conclusions. This is the same breathalyser machine that the police use.