Defending a Drinking and Driving Charge

By Ron Jourard, B.A., M.A., Ll.B.

The most common drinking and driving offence in Canada is Over 80 mgs. Also referred to as Excess Alcohol, this charge is laid if breath or blood tests show that the driver of a motor vehicle (or person in care or control) has a blood alcohol concentration of more than 80 mgs in 100 ml of blood.

(Care or control means being in charge of a motor vehicle. You are presumed to be in care or control if you are sitting – awake or asleep - in the driver’s seat, even if the engine is off.)

Police will demand breath samples

If you were arrested for drinking and driving, either because you blew a fail on a roadside screening device or displayed signs of alcohol impairment, police will demand you to undergo breath tests to determine the amount of alcohol in your blood. Police will take two breath samples; the lower test result is presumed to be your blood alcohol concentration (BAC) at the time of driving (or care or control).

To secure your conviction on a drinking and driving charge involving breath samples, the tests must be conducted with a breath instrument approved for use in Canada such as the Intoxilyzer 5000C or 8000C.

Breath instrument malfunction or operating error

According to a 2012 Supreme Court of Canada ruling, the only way you can raise a doubt about the reliability of breath test results taken within two hours of the offence, is by showing that the breath instrument malfunctioned or that police did not operate the device properly. If the tests are taken outside two hours, evidence that you consumed insufficient alcohol to result in breath readings exceeding 80 mg in 100 ml of blood at the time of the offence ostensibly can still raise a doubt about your guilt. Thus, if you provide evidence of alcohol consumption that is not rejected by the judge along with evidence of a forensic toxicologist calculating that the amount of alcohol in your blood at the time of driving (or care or control) was within the legal limit, you are entitled to an acquittal.

Forensic toxicologist required

To demonstrate at trial breath instrument malfunction or operator error you will likely need to retain the services of a forensic toxicologist with expertise on breath instruments. An expert on the body's absorption and elimination of alcohol, a forensic toxicologist can also calculate your BAC based on your evidence of alcohol consumption.

If you are charged with a drinking and driving offence in Canada and want to check whether your BAC may have been within the legal limit, use the BAC calculator on this website.

If you have not been tested to determine the rate at which alcohol eliminates from your blood, use a rate of 10 mg per 100 ml of blood per hour. Although your elimination rate is probably faster, it will help to raise a reasonable doubt in court (where such evidence is still deemed probative) as to your guilt if a calculation based on the slowest rate puts your BAC at the time of the alleged offence within the legal limit. See the Supreme Court of Canada's 2008 ruling in R. v. Gibson.

Mr. Jourard is a Toronto criminal lawyer specializing in defence of drinking and driving charges. For more information see his website.