BAC, Individual Factors and Driving Risk

What BAC Measures

Blood alcohol concentration (BAC) expresses the amount of alcohol in a given volume of blood. In the percentage convention used in SIR, a BAC of 0.08% means 0.08 grams per 100 mL of blood, or 80 milligrams per 100 mL. A BAC of 0.05% means 50 milligrams per 100 mL. These are concentration values, not percentages of the beverage consumed.

A beer marked 5% alcohol by volume (ABV) describes alcohol in the beer. It does not mean that drinking it produces a 5% BAC. Beverage volume and strength help determine dose; BAC depends on absorption, distribution and elimination within a particular person. Confusing ABV with BAC produces both arithmetic errors and dangerous decisions.

The official course identifies approved screening devices and blood tests as measurement methods. A server’s visual estimate is not a chemical measurement. Do not invent an exact BAC from slurring, eye colour or how confident the customer sounds.

Driving Rules Are Not Service Permissions

The course highlights the federal 0.08% threshold and BC’s 0.05% roadside range. Current federal law includes both impaired operation and the offence of having at least 80 mg per 100 mL within two hours after ceasing operation, subject to statutory exceptions. A person can also be impaired below 0.08%. The number is not permission to drive after drinking up to that point.

BC uses roadside measures under the Motor Vehicle Act, including the Immediate Roadside Prohibition system. A “Warn” at the relevant 0.05% range can result in a 3-, 7- or 30-day prohibition depending on the driver’s recent record. A “Fail” or qualifying refusal can result in a 90-day prohibition. These consequences do not mean a server should aim to keep customers just below a numerical threshold. Learner and novice drivers must meet zero-alcohol and drug restrictions.

For service, Act section 61 prohibits selling or serving to someone intoxicated or showing signs of intoxication. That rule does not wait for a blood test or a 0.08% estimate. If a patron is unwell or impaired by another substance, further alcohol can add risk even when the alcohol dose seems small.

Amount and Rate of Consumption

The amount of pure alcohol and the rate of intake are separate factors. Two large strong beers may deliver more alcohol than several light beers. Drinking the same total rapidly gives the body less time to process it than spreading it across a longer period. Standard-drink calculations are therefore useful, but a fixed count cannot identify a universal safe allowance.

Do not subtract exactly one drink every hour and declare the person sober. The SIR hourly processing estimate is approximate, absorption can continue after drinking ends and people differ. Continue to observe the patron and plan safe transport when needed.

Weight, Body Composition and Sex

All else being comparable, a smaller person will often experience a greater alcohol concentration from the same dose than a larger person. Body composition also matters: muscle contains more water than fat, and alcohol distributes mainly in body water. Two people of the same weight can respond differently.

The course discusses average sex-related differences in body water and alcohol processing. These averages do not justify predicting an individual’s BAC from their appearance or gender identity. Avoid guaranteed comparisons such as “every woman will become intoxicated first.” Monitor each guest rather than assign a larger service allowance to a group based on assumptions.

Food, Age and Health

Food can slow absorption; an empty stomach can permit quicker effects. Food is a preventive tool, not a cure for alcohol already in the blood. An older person or someone in poor health may respond differently from a younger, healthy person. A familiar customer may no longer respond as they did years ago. Medication can change impairment and safety even without changing the alcohol concentration in the expected way.

Mood, Environment, Fatigue and Tolerance

Loud music, crowding, seating arrangements and interactions can influence drinking pace and behaviour. An already angry guest may become more disruptive as inhibition drops; alcohol is not a reliable treatment for stress. Fatigue can worsen performance and make a person more vulnerable. Do not claim a particular amount of tiredness always equals a precise BAC increase.

Tolerance can mask early signs. Someone who says they “hold their liquor” still needs monitoring based on amount, rate and observed changes. A lack of obvious staggering does not establish safe driving, and a small local tab does not rule out prior consumption elsewhere.

Comparison Scenario

Two diners each order a large wine. One arrived after a meal; the other reports no dinner, a long shift and prior drinking at another venue. The server cannot calculate their exact BAC from those facts, but should recognize that equal orders do not imply equal risks. Talk with each person, consider consumption history, offer alternatives and involve a colleague when concerns arise. Stop alcohol at signs of intoxication and address medical or departure risks directly.

Sources checked October 9, 2026

Official SIR manual, pages 39–48; Criminal Code, section 320.14; BC impaired driving.