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# Blood alcohol concentration (BAC)

A concentration expressed in mass of alcohol divided by volume of blood. Stated in the Criminal Code of Canada as "80 mg of alcohol in 100 mL of blood". It is expressed as a number and a reference and so the Weights and Measures Act of Canada applies. The reference is to both the SI unit gram(1/1000 kilogram) and the SI unit metre (1 litre is one cubic decilitre and 1 mL is 1/1000 litres.)

English section 320.14(1)(b) "a blood alcohol concentration that is equal to or exceeds 80 mg of alcohol in 100 mL of blood".
French section 320.14(1)(b) "une alcoolémie égale ou supérieure à quatre-vingts milligrammes d’alcool par cent millilitres de sang"

A "quantity" in metrological terminology. "Quantity" is extensively defined in the international literature. VIM 1.1 "property of a phenomenon, body, or substance, where the property has a magnitude that can be expressed as a number and a reference", VIM describes an example of a quantity: "amount-of-substance concentration of ethanol in wine sample". Note that Parliament has prohibited a concentration, not just a rough estimate: "a blood alcohol concentration that is equal to or exceeds 80 mg of alcohol in 100 mL of blood". Connect construction and application of the Criminal Code with another federal statute, the Weights and Measures Act. They need to be read together.

Many lawyers have difficulty separating the concept of blood alcohol concentration (BAC) from breath alcohol concentration. (BrAC). In Canada we criminally prohibit a blood alcohol concentration of 80 mg/100mLs and above, whether the evidence comes from a blood sample or from a breath sample. In other jurisdictions the criminal delict is described as a prohibited breath alcohol concentration. Since we usually, in Canada, for forensic purposes, measure for blood alcohol concentration using breath instruments, we need to convert the measured breath alcohol concentration. This is done by multiplying an assumed blood:breath ratio of 2100:1. Not all persons, at all times, have a ratio of 2100:1. 2100:1 is a convention based on an average. The average does not apply to all human beings. Some people who suffer from disabilities (e.g. being female, being from a racial minority, suffering from lung disease, being over age 55, or a combination thereof) may have BBRs less than 2100:1. Under the old pre -C-2 and pre-C-46 laws an individual with a disability (e.g. elevated body temperature (R. v. St‑Onge Lamoureux, 2012 SCC 57 (CanLII), [2012] 3 SCR 187, referencing R. v. Kasim, 2011 ABCA 336 para. 3-5) or low BBR (R. v. Phillips, 1988 CanLII 198 (ON CA))) could empirically establish pre-C-2 "evidence to the contrary" or pre-C-46 "evidence tending to show" to rebut the Criminal Code presumption of BAC at time of driving/care or control. Persons with a disabilitiy are now conclusively proven to have the same BBR as the average person, without the possibility of rebuttal through evidence contradicting the presumption.

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