Breath-alcohol testing is a cornerstone of impaired driving enforcement, widely used in Canada to determine whether drivers are over the legal blood-alcohol concentration (BAC) limit. However, new scientific findings shed light on a significant problem with this method of testing: the variability of the blood/breath ratio (BBR), which directly impacts the accuracy of breath-alcohol test results. This variability raises important questions about how reliable breathalyzer readings truly are, and has serious implications for those facing impaired driving charges.
At the heart of the issue is the BBR, the proportionality factor used to convert a breath-alcohol concentration (BrAC) into an estimated BAC. The standard BBR, used in all breath-alcohol testing devices in Canada, is assumed to be 2100:1. This means that 2100 mL of breath is considered equivalent to the alcohol content of 1 mL of blood. However, as discussed in a recent article by Dominick A. Labianca, The Variability of the Blood/Breath Ratio and Its Impact on the Results of Breath-Alcohol Analyses (2023), this ratio is far from fixed and can vary significantly between individuals.
What the Science Says About the Blood/Breath Ratio
Labianca’s findings reveal that the BBR can fluctuate widely, with a range of 1657:1 to 2903:1 in 99% of the population. For most individuals, the BBR tends to fall between 1900:1 and 2400:1, but the fact that it varies at all introduces a margin of error into breathalyzer readings. This means that someone who registers over the legal limit on a breath test could, in reality, have a BAC below the legal threshold. Conversely, the opposite is also possible, with some individuals potentially having a higher BAC than the breathalyzer indicates.
The variability is influenced by factors such as the individual’s metabolism, health status, and whether they are in the absorptive or post-absorptive state of alcohol processing. For example, during the absorptive phase (when alcohol is still being absorbed into the bloodstream), breath-alcohol levels tend to be higher than blood-alcohol levels, potentially inflating breathalyzer results. Conversely, in the post-absorptive phase, the results may more accurately reflect the true BAC.
Legal Implications for Defence Lawyers
This variability in the BBR is a critical factor that defence lawyers must consider in impaired driving cases. The assumption that the BBR is constant at 2100:1 underpins the accuracy of breath-alcohol tests, but Labianca’s research highlights that this assumption can lead to inaccuracies in determining a person’s actual level of impairment. For defence lawyers, these findings offer a basis to challenge breathalyzer results and introduce reasonable doubt into the accuracy of the evidence presented against their clients.
In criminal cases, where the prosecution must prove guilt beyond a reasonable doubt, demonstrating that breathalyzer results could be flawed due to BBR variability might be able to significantly strengthen a defence — but the law is not settled in Canada as to whether this defence is even one that is permitted. Because the Criminal Code prohibits many challenges to breath test operation and reliability, challenging it through the use of a different BBR may not be possible under the law as it is written.
This means that the law may potentially prohibit people from proving their innocence.
This has not yet been litigated so the answer is far from definitive and we are certainly interested in taking on such a challenge with the right evidence.
Breath-alcohol readings are often treated as conclusive in Canadian law, but Labianca’s research shows that this confidence may be misplaced.
Implications for People Facing a DUI Charge in British Columbia
In British Columbia, where Immediate Roadside Prohibitions (IRPs) and Administrative Driving Prohibitions (ADPs) can be issued based on breathalyzer results, the variability of the BBR has significant implications for people facing DUI charges. Under the current system, police officers use breathalyzer devices to measure BrAC at the roadside, and drivers who register over 0.08 BAC can face immediate sanctions, including license suspensions, vehicle impoundment, and fines. Even those who register between 0.05 and 0.08 may face penalties under the province’s ‘warn’ range.
Given the reliance on breathalyzer results in this process, the BBR’s variability can mean that some drivers are penalized based on inaccurate readings. For instance, a driver in the absorptive phase of alcohol metabolism might register a higher BrAC, leading to an IRP even though their actual BAC is below the legal limit. The consequences of these sanctions are significant, ranging from personal inconvenience to career implications, particularly for those in professions that require a valid driver’s license. This makes it imperative for individuals facing DUI charges to understand that breathalyzer results are not infallible and may be open to challenge based on scientific evidence.
For those seeking to dispute an IRP or ADP, the findings about BBR variability provide a potential foundation for requesting a review of the evidence. Your lawyer in an IRP or ADP review hearing can argue that the breathalyzer reading may not accurately reflect the individual’s true BAC due to the inherent variability in how breath and blood-alcohol levels correspond.
In these cases, it may be possible to have the prohibition revoked, especially if expert testimony can be provided to explain how breathalyzer readings can be influenced by individual biological differences, and provided there is evidence of a person having a BBR that is not 2100:1.
Expert Testimony and Limitations
Labianca’s findings also open the door to the use of expert testimony in impaired driving cases. Toxicologists or other scientific experts can explain to the court how BBR variability works and how it can introduce errors into breath-alcohol readings. They could also perform individual testing on people to determine their specific BBR, although finding a toxicologist able to measure blood alcohol levels contemporaneously with breath tests is a big ask.
The unavailability of the processes to readily establish these defences is a concern when it comes to the possibility of wrongful conviction.
Educating Judges
Educating judges about the limitations of breath-alcohol testing is another important strategy. Many people, including those in the legal system, assume that breathalyzers are infallible. However, by highlighting the variability in the BBR, defence lawyers can create a more nuanced understanding of how these tests work and why they should not be accepted without scrutiny.
Judges need to understand that the science behind breath testing is not as straightforward as it might seem. Breath-alcohol testing is subject to biological and technical factors that can affect its accuracy. Explaining these complexities can help ensure that breathalyzer results are not given undue weight in court.
The Need for Vigilance in Impaired Driving Cases
Relying on averages means that people who are not average at a particular point in time may be wrongfully accused and wrongfully punished. The variability of the blood/breath ratio has far-reaching implications for impaired driving cases, particularly in British Columbia, where breathalyzer results are often used to impose immediate penalties.
DUI lawyers must be vigilant in questioning the reliability of breathalyzer results and prepared to educate judges and even tribunals about the potential for error in these tests. Labianca’s research provides a strong foundation for challenging breath-alcohol readings, and lawyers who leverage this information will be better equipped to defend their clients.
Scientific evidence used to play a significant role in DUI cases in the courtroom but this changed with the 2008 Criminal Code amendments. In an era where scientific evidence plays a crucial role in the courtroom in many other regards, it is hard to reconcile punishing people who are on the wrong side of a software decision by a breathalyzer manufacturer.
For defence lawyers in British Columbia and beyond, being aware of the variability in the blood/breath ratio is not just a matter of scientific curiosity—it is a vital tool in ensuring that justice is served.
