What is impairment?

Impairment is a state in which a person has reduced mental and/or physical functions and abilities. The Occupational Health and Safety Regulation (Part 4.19) approaches impairment in terms of how it impacts a worker’s ability to carry out their work without creating an undue risk to themselves, or anyone else.

Impairment can be caused by:

  • alcohol or drugs (including prescription, over-the-counter and illegal drugs)
  • fatigue
  • medical conditions
  • mental health issues (e.g., depression or anxiety)
  • temporary, situational stressors (e.g., grief and financial problems)

Impairment levels, driving and the law

Alcohol: Under BC law, a driver who provides a breath sample with a blood alcohol content (BAC) of 0.05 or more is legally impaired and subject to penalties.

Cannabis: Under the Criminal Code, there are two prohibited levels for tetrahydrocannabinol (THC), the primary psychoactive component of cannabis.

  • It is a less serious offence to have between 2 nanograms (ng) and 5 ng of THC per ml of blood.
  • It is a more serious offence to have 5 ng of THC or more per ml of blood.

Alcohol and cannabis: The prohibited levels of alcohol and cannabis, when found in combination, is 50 mg or more of alcohol per 100 ml blood (0.05 BAC) and 2.5 ng or more of THC per ml of blood.

Other drugs: Having any detectable amount of LSD, psilocybin, psilocin ("magic mushrooms"), ketamine, PCP, cocaine, methamphetamine or 6-mam (a metabolite of heroin) in your system within two hours of driving is also prohibited. Peace officers who suspect a driver is affected by drugs may impose immediate prohibitions.

BC’s Graduated Licence Program applies tight restrictions to drivers who hold a learner’s (L) or novice (N) licence. If they drive while they have any alcohol or drugs in their system, they face immediate consequences.

Fatigue: There is no universally accepted measure or threshold to determine impairment due to fatigue. However, studies show that after 17 to 19 hours without sleep human performance on some tests was equivalent or worse than that at a BAC of 0.05%. According to the National Sleep Foundation’s Sleep in America poll, 60% of Americans have driven while feeling sleepy and 37% admitted to falling asleep at the wheel in the past year.

Commercial vehicle drivers must comply with Hours of Service rules. The basic restrictions allow no more than 13 hours of driving a day and no driving after 14 hours of being on-duty. Although other drivers may not be subject to Hours of Service laws, they are every bit as prone to fatigue. Consider building similar restrictions into your fatigue management plan.

What this means:

  • A worker is impaired when their ability to drive is affected such that if they were to drive, they would create undue risks or endanger themselves, or others.
  • If a worker drives while they are impaired, the worker, their supervisor and their employer may be subject to liability and penalties under the Motor Vehicle Act, the Workers Compensation Act, civil law and criminal law.
Keep in mind that driving while impaired can invalidate insurance policies, exposing the driver and the vehicle owner to significant liability.

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What is impairment?

What's an employer to do?

 Develop and implement an impairment policy

 Educate employees about the policy

 Educate managers and supervisors



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