Blog - On the Intricacies of Breath Alcohol Testing


Breath alcohol concentration (BrAC) measured sing an electronic breath testing device  (i.e. a breathalyser) is the accepted practice to measure alcohol use. The current Australian Standard ('AS 3547:1997 breath alcohol testing devices for personal use') is currently under review, and after a period of public comment the revised standard will be published, hopefully within the year.

It is timely, then, to describe some key points about breath alcohol testing in practice.

The first point is that breath testing devices are finely tuned, sensitive pieces of electronic equipment.  This is a part of the Standard, requiring them to be regularly serviced and calibrated so that they perform at peak efficiency and accuracy. This means they must operate under a wide range of environmental conditions, including large variations in temperature, humidity, locations near electrical and magnetic fields, etc. In addition, the responsiveness of the instruments to previously recorded high alcohol concentrations, so that they must return rapidly to a state where they can accurately record lower (or zero) alcohol concentrations without any carryover from the previous specimen.

So it is important that with such a sensitive instrument, we should handle and use it carefully, and report results to the level of accuracy the instrument is capable of.  That means that when we record a BrAC, it should be to 3 decimal places. That is, a reading of 0.000g/210L rather than 0.00g/210L; or 0.049g/210L rather than 0.04g/210L.  The last decimal character can make a difference when interpreting BrAC data and comparing with limits prescribed in a workplace drug and alcohol policy.

This takes us to the second point.  The units of measurement of BrAC described above are grams alcohol per 210 litres of exhaled breath. Policies I have seen often describe breath alcohol readings as %. This is a misinterpretation. The true index of alcohol influence is Blood Alcohol Concentration (BAC) measured in grams per decilitre of blood, or %. However, we are neither capable of - nor authorised to - take blood specimens in workplaces to estimate BAC.

Alcohol in blood is in equilibrium with alcohol vapour in the alveoli of the deep lung.

This means alcohol in breath is an excellent relative index of BAC.  The trick in using breath alcohol instruments is that the units of BrAC have been selected to give the same numerical value (expressed as g/210L breath) as the corresponding BAC (expressed as %). That is it…electronic juggling of units to give us matching numerical values. But the units are important, especially when a breach of policy ends up in a tribunal, where a misstatement of a concentration measured in breath (% instead of g/210L) may provide sufficient uncertainty as to the way the test was conducted as to allow a finding in favour of the intoxicated or impaired worker.

And finally, as well as recording BrAC accurately, the device must also read zero BrAC accurately, too.

Zero BrAC, or 0.000g/210L is an important number. Some practitioners may decide that they should adjust the zero recording point to some other ‘true’ alcohol concentration (say 0.019g/210L). They do this to give workers the benefit of the doubt (allowing for small breath alcohol concentrations to be seen as zero when tested), or to align with policies where workers are permitted a threshold of ‘acceptable’ BrAC. This approach, known as "zero masking", is not recommended. The instrument should always record the accurate BrAC, as measured by the device. It is the place of the workplace policy to determine the BrAC at which any action or sanction should be implemented. Again, in a situation with a worker appealing against some sanction in a tribunal, an instrument that does not record true BrAC will not be viewed favourably.

In the hands of competent, trained Collectors, breathalyser instruments are a valuable tool in maintaining a safe workplace. We should not treat them poorly.

Boilerplate John