Canada: Rebutting The Breathalyzer Presumptions

Moving Beyond the Theoretical, Towards Concrete Evidence

In R. v. Cyr-Langlois,1 the Supreme Court of Canada offered clarification on the type of evidence that is required to rebut the presumptions of accuracy and identity applicable to breathalyzer test results under section 258(1)(c) of the Criminal Code ("Code").2 In doing so, Wagner C.J., writing for the majority, confirmed that the evidence must amount to more than conjecture or speculation. This case is significant for defence lawyers, as it demonstrates that an accused will likely need to adduce concrete factual evidence in order to rebut the breathalyzer presumptions.

Statutory Presumptions

Section 258(1)(c) of the Code contains two presumptions applicable to breathalyzer results: the presumptions of accuracy and identity. According to the presumption of accuracy, the certificate of the technician responsible for administering the breathalyzer test is presumed to provide an accurate determination of the person's blood alcohol level ("BAC") at the time that the breath samples were taken.3 According to the presumption of identity, a person's BAC as shown by the test results is presumed to be the same as his or her BAC at the time of the alleged offence.4 If an accused produces evidence that casts doubt on the reliability of the test results, the presumptions may be rebutted.

Facts and Case History

The accused, Marc Cyr-Langlois, was stopped by two police officers while driving. He was arrested at the scene and was taken to the police station. The accused received two breathalyzer tests at the police station. Both results were over the legal limit. The accused was then charged with operating a motor vehicle while impaired and operating a motor vehicle with a BAC exceeding 80 mg of alcohol in 100 ml of blood.

At trial before the Court of Québec, the accused argued that the qualified technician failed to observe him for a period of 15 or 20 minutes before administering each breathalyzer test. He submitted that this was a breach of the duty to operate the breathalyzer properly and that it was sufficient to rebut the presumptions of accuracy and identity applicable to breathalyzer results. The trial judge found that the fact that the procedure had not been followed was sufficient to raise a reasonable doubt as to the reliability of the results. The accused was therefore acquitted on the second charge, and the Crown had no evidence to adduce on the first charge.

The Crown appealed the trial judge's decision, and the Québec Superior Court set aside the acquittal and ordered a new trial. A majority of the Québec Court of Appeal restored the acquittal. The Court of Appeal characterized the analysis of the rebuttal evidence as a factual exercise and held that the Superior Court had erred in intervening absent an unreasonable assessment of the evidence by the trial judge.

The Crown appealed to the Supreme Court of Canada. On appeal, the Supreme Court was required to consider the nature and scope of the evidence that is needed to rebut the statutory presumptions of accuracy and identity.

Rebutting the Statutory Presumptions

Citing the case of R. v. St-Onge Lamoureux,5 Wagner C.J. confirmed that in order to rebut the presumptions in section 258(1)(c), an accused must adduce evidence tending to show that the malfunctioning or improper operation of the test instrument casts doubt on the reliability of the results.6 In particular, the evidence must relate directly to deficiencies in the maintenance of the instruments or the test process.7 To discharge the burden of rebutting the statutory presumptions, two conditions must be met:

  1. The accused must adduce evidence relating directly to the malfunctioning or improper operation of the test instrument, and;
  2. The accused must establish that this defect tends to cast doubt on the reliability of the results.8

Wagner C.J. also noted that while abstract evidence alone may raise a reasonable doubt as to the reliability of the results, it is more likely that evidence which relates more concretely to the facts in issue will be required.9 In order to raise a reasonable doubt as to the reliability of the results, Wagner C.J. confirmed that the evidence must extend be beyond the realm of conjecture or speculation.10

Application to the Case

In his analysis, Wagner C.J. focused on whether there was evidence that the improper operation of the test instrument tended to cast doubt on the reliability of the results. He concluded that although the qualified technician failed to adhere to the 15 to 20 minute observation period, there was no evidence that this improper operation raised a reasonable doubt as to the reliability of the results.11 In addition, he was not prepared to find that such a procedural defect could, in theory, compromise reliability so as to raise a reasonable doubt.12 He further stated that acceptance of theoretical evidence based on speculation would be a misrepresentation of the accused's burden.13 Given that there was no evidence which cast doubt on the reliability of the results, the Court allowed the appeal, set aside the acquittal, and ordered a new trial.


In her dissent, Côté J. stated that requiring an accused to adduce concrete evidence imposes a heightened obligation on them to cast doubt on the accuracy of the breathalyzer test results, which she explained was contrary to the reasoning in St-Onge.14 She indicated that where evidence tends to show that a defect increased the possibility of an inaccurate result, reliability is affected and the accused has met their burden.15 As such, she was of the view that to rebut the presumptions, it is sufficient for an accused to produce evidence showing that a recommended procedure was not followed and that the purpose of the procedure is to ensure the reliability of the results.16 Côté J., therefore, concluded that the trial judge had not erred and would have dismissed the appeal.

Key Takeaways

This case illustrates that defence efforts to rebut the breathalyzer presumptions in section 258(1)(c) will be more challenging. Judges will be looking for concrete factual evidence, as opposed to theoretical evidence, to raise a reasonable doubt as to the reliability of the test results. As a consequence, defence counsel will have less creative defences that can be relied on to rebut the statutory presumptions.

With the legalization of cannabis, it will be interesting to see whether a similar approach will be taken with respect to the evaluative procedures that will be implemented for drug-impaired driving.


  1. 2018 SCC 54 [Cyr-Langlois].
  2. Criminal Code, RSC 1985, c C-46.
  3. R v St-Onge Lamoureux, 2012 SCC 57 at para 6 [St-Onge].
  4. Ibid.
  5. St-Onge, supra note 3.
  6. Cyr-Langlois, supra note 1 at para 3.
  7. Ibid.
  8. Ibid at para 4.
  9. Ibid at para 14.
  10. Ibid at para 15.
  11. Ibid.
  12. Ibid.
  13. Ibid at para 19.
  14. Cyr-Langlois (dissent) at para 35.
  15. Ibid at para 37.
  16. Ibid.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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