Over 80mg is an offence under section 253(1)(b) of the Criminal Code. This section makes it an offence to operate or be in care and control of a motor vehicle with over 80mg of alcohol in 100mL of blood. This is what your breath test results are primarily used for, proving the “over 80” offence. This offence is far more technical in nature than the “impaired driving” offence. A person cannot tell the difference between when their blood alcohol concentration is 75mg of alcohol in 100mL of blood and when it is 85mg of alcohol in 100mL of blood, yet there is a big difference if you are considering taking a drive. In order to prove this offence, the prosecutor has to present admissible evidence of your blood alcohol concentration at the time of driving. This is somewhat challenging, as your blood alcohol concentration is not measured at the time of driving, but only later at the police station (or mobile RIDE unit). They show your blood alcohol concentration at the time of driving by relying on the “presumption of identity”, which allows the judge to conclude that your blood alcohol as measured at the station is accurate to the time of driving, provided that a number of preconditions are met.