James Brown , Alcolizer Technology shares his views on Alcohol testing, Blood vs Breath

As the prevalence of medicinal cannabis use and unprescribed cannabis consumption for conditions like insomnia, pain relief, and anxiety continues to rise among adults in Australia and New Zealand, a growing concern arises.

“Many patients opt for cannabis due to the perceived tolerability of its side effects in comparison to other medications. Nevertheless, it is paramount for doctors to be vigilant in recognizing and appropriately managing these side effects and related issues. ”

Alcohol Testing: Blood vs. Breath

The concept of testing for alcohol (specifically ethanol) impairment via human breath is so well established in the AOD and law enforcement sectors that few people give it any thought. By exploring some of the history and evolution of alcohol impairment testing, we can develop a better understanding of how and why breath testing is conducted the way it is, particularly the industry standard of g/210L as the unit of measure. 

Alcohol breath testing in Australia has a long history, going back to the days when police used qualitative methods such as blow-in-the-bag crystal devices. For legal purposes, however, alcohol impairment was gauged by measuring the amount of alcohol present in a donor’s blood. Blood Alcohol Content (BAC) was measured as a mass/volume measure of alcohol per unit volume of blood, generally grams of alcohol per 100 millilitres of blood. This was often abbreviated to percent, i.e., (grams) per 100 (millilitres). Globally, there are various units of measure including mg/100mL, mg/mL, mg/dL, g/L, and mass/mass measurements such as g/kg or mg/g. 

As individual states refined their legislation, a legal limit of 0.050 g/100mL became standard across the states, and a limit of 0.05 became well ingrained in public perception. 

Understandably, the use of blood testing was an expensive and invasive process, requiring trained medical staff to draw blood and perform analysis. With the invention of reliable breath alcohol testing equipment, police began using the new breath testers in their law enforcement operations, and eventually all states adjusted their legislation to allow the use of evidentiary breath alcohol testers as the primary evidence in the conviction of drink driving offences. 

Nowadays, all states have extended their legislation to specify legal limits as either Blood Alcohol Content (BAC) OR Breath Alcohol Content (BrAC). 

For example, in Queensland, under the Transport Operations (Road Use Management) Act 1995, section 79A, a person is over the general alcohol limit if they have more than 50mg/100mL of alcohol in blood or more than 0.050g/210L of alcohol in breath. The consistency of the “0.05” public message is clear in the legislation but has some implications, as we will see. The use of 210 litres of breath as a unit of measure may seem absurd to the layperson but allows the 0.05 public message to be preserved. 

Police typically use a two-step process for drunk driving convictions. Drivers are initially tested with a Preliminary Breath Tester (PBT). If donors are found to exceed the legal limit on a PBT, they undergo a secondary Evidential Breath Test (EBT) using an instrument that has more rigorous processes for legal metrology. In this two-step process, drivers are charged based on the result of an Evidential Breath Test, and as such, conviction is based on breath measurement alone. 

The ratio of blood alcohol to breath alcohol is called the partition ratio. In Australian law enforcement, the partition ratio is 50mg/100mL to 0.050g/210L, which reduces to 2100:1. Therefore, law enforcement uses a partition ratio of 2100:1. This is a conservative figure, with a study (Cowan, Burris, Hughes, Cunningham, 2010) indicating a mean partition ratio of 2380:1 with a standard deviation of 119. This indicates that donors are more likely to hit the blood limit before they hit the breath limit; i.e., on average, by the time donors report 0.050g/210L in breath, they would be well over the limit in blood at 0.057g/100mL. Law enforcement agencies can be confident that donors are impaired with respect to blood measurements when they exceed the limit for breath. 

Beyond law enforcement, the use of alcohol testing for impairment, fitness for work, and medical applications is now well established and helps protect millions of people every year. In these professional applications, the industry standard is the Australian AS3547 series of standards. Since the 2019 publication, breath alcohol testing devices are required to produce results in g/210L – grams of ethanol per 210 litres of breath. This is a measure of Breath Alcohol Content (BrAC). This is a consistent approach, with donor breath being exhaled, sampled, measured, and displayed as a breath measurement. 

In contrast, before 2019, the 1997 edition of the standard required breath alcohol testing devices to display results in a blood measurement of g/100mL. Because breath testers were sampling breath but displaying a blood reading, this was considered an inferred result because blood was not directly measured. On the contrary, the result was established by measuring the donor’s breath and, using a partition ratio of 2300:1, an inferred blood alcohol concentration was calculated and displayed to the operator. 

Of particular note is the use of a 2300:1 partition ratio. Due to the difference in partition ratio, a donor tested on consumer equipment would have a different (slightly higher) numerical reading compared to if they had tested on a police device. While the use of a 2300:1 partition ratio is much closer to the actual donor partition ratio than the 2100:1 used in law enforcement, the decision was made to be consistent with law enforcement, and under the latest 2019 edition of AS3547, the g/210L (BrAC) unit of measure was adopted. 

The change in the AS3547 unit of measure has a subtle implication for the use of alcohol breath testing and company policies. Prior to the 2019 standard, businesses would develop their AOD policies around the best practice at the time, which was AS3547:1997, and impairment tolerance would be quoted as a blood alcohol content. With the release of the 2019 standard and the move to breath alcohol measurements, it is prudent for companies to update their AOD policies in line with the latest best practice, AS3547:2019. 

In practice, many organizations have a zero tolerance, and in theory, zero is still zero, whichever unit of measure is used. However, to avoid any legal confusion or for organizations that use a non-zero impairment limit, it is recommended that organizations update their AOD policies similar to law enforcement and quote limits in both blood or breath. 

In general, both law enforcement and domestic OH&S applications have moved to breath alcohol testing. Many years have shown this to be a very reliable and non-intrusive measure of impairment. With the release of the AS3547:2019 standard, the quality and reliability of the industry have been lifted, and it will serve the Australian public well for many more years. 

James Brown
Alcolizer Technology