Breathalyzer readings can be confusing, especially for new users. Confidence in the accuracy of these breathalyzers is essential, but users should always be cautious when unexpected results are obtained, either higher or lower than what common sense is suggesting. Its not always an error with the machine that explains these. Alcohol metabolism is complicated and multifactorial so some variation is to be expected.
The first important consideration is what scale is being displayed. So you buy a digital breathalyser and blow into it. It displays the breath alcohol level – right ? ~ wrong, in most cases anyway. Breathalyzers bought for personal or business use almost universally display the equivalent Blood Alcohol Concentration, normally abbreviated to BAC. The on board electronics do the conversion from the breath measurement to BAC which will usually be displayed either as a %BAC or mg/100ml BAC. The simple explanation for this is that almost all the written legislation in Europe refers to BAC cut off levels for either HSE, employment or driving law, so to keep it simple the manaufacturers set the breathalyzers to display BAC.
There are multiple display scales for breathalyzer readings, in fact 6 are commonly used internationally, so it is vital you know what display reading your breathalyzer is set to display. In most models of breathalyzer this is pre-set at manufacture, in some more expensive breathalyzers you may have an option to select the display reading scale. Understanding the scale of the display is critical to interpreting the readings.
Next check the specificity of the sensor. This will be quoted by the manufacturer and guides you on the best accuracy the sensor is capable of working at at the variation in the displayed readings you can expect at a set level of alcohol. For example is a sensor has a specificity of +/-0.05%BAC then at 0.10%BAC alcohol the display may vary from 0.95%BAC to 0.15%BAC on the same sample of breath, so do not expect 3 successive readings taken in quick succession to always be identical. They should not vary by more than the specified selectivity, and if they do, look for a reason, ie poor blow technique, a blocked inlet, or a sensor which is losing its calibration settings and needs changing.
What’s sensor calibration ? Well its the setting up of the electrochemical sensor module at set alcohol levels to tell the electronics what to display at these levels, its the accuracy set up, like tuning a car. Problem is its not set for life and tends to be lost with time and use, so most breathalyzer sensors need changing for a fresh sensor every 3-6 months of 300 tests, which ever comes first. So the bad news is you can’t buy one of these breathalyzers and expect it to work a year later without some service costs, expect to change sensors regularly if you expect an accurate reading.
Physiology messes up charting alcohol metabolism. Thats why you will not find nice charts for what your blood alcohol will be 1 hr after a double gin and tonic. You must allow for the dilution effect, so how much tonic you take, to start with, the stomach contents can slow or speed absorption, all affecting peak blood levels and times, then there is body mass, circulatory volume, liver function, other enzyme competion or pre-priming effects, etc etc etc. Bottom line is no two people metabolise alcohol identically, and same person will not do it reliably from week to week.
The guide is, you clear about a unit per hour. But it is just a guide. Use the breathalyzer readings done every 20 minutes to find out your personal clearance, but dont rely on it to be the same the next day, or with a different alcohol.
Also remember the alcohol level is not an indication of ability or lack of it to perform a task. BAC is not related to hangover, nausea, headache or other alchol effects, its is just a spot level in time reading of the blood level. If taken within an hour of the last comsumption, then the level may still rise. Interpreting readings can be impaired by alcohol. Performing a self test, can be impared by alcohol. Breathalyzer readings are best taken by sober people who will monitor the technique and interpret the readings for the alcohol consumer.