Marijuana in the Canadian Workplace

In Canada, Cannabis (Cannabis / Marijuana, Δ 9 -Tetrahydrocannabinol, THC) legalization is happening. The Federal Government has set November, 2016 as the date for putting forth a framework and is currently soliciting detailed feedback on a variety of topics from Canadians. This is of course, following in suit with some of our American Sister States (2012: Colorado & Washington became the first states to legalize the recreational use and sale of marijuana. Since then, 2 additional states plus the District of Columbia have jumped on the bandwagon, while 18 others have legalized Medical Marijuana), legalization is around the corner for Canada. This has caused concern for employers regarding workplace safety and how to manage drug testing.
As of July 2016, this Schedule II drug (Schedule I in the USA) is still considered Federally illegal in both the US & Canada under the Controlled Substances Act (although many states have already begun legalization). However, as employers it is a critical time for us to become more educated on impairment, risk, and drug testing methods in the workplace.
The California NORML has completed extensive research on drug testing detection, specifically aimed at Marijuana. Drug testing may be completed by analysis of urine (the most popular, cost effective test type), blood, hair and saliva. For now, we'll focus on the most productive method for THC Testing in the body - urine testing.
The California NORML Guide explains:
'The most popular kind of drug test is the urine test, which can detect marijuana for days or weeks after use. Note that urine tests do not detect the psychoactive component in marijuana, THC (delta-9-tetrahydrocannabinol), and therefore in no way measures impairment; rather, they detect the non-psychoactive marijuana metabolite THC-COOH, which can linger in the body for days and weeks with no impairing effects.'
Unlike urine tests, blood tests detect the active presence of THC in the bloodstream. In the case of smoked marijuana, THC peaks rapidly in the first few minutes after inhaling, often to levels above 100 ng/ml in blood plasma. It then declines quickly to single-digit levels within an hour.
High THC levels are therefore a good indication that the subject has smoked marijuana recently.
THC can remain at low but detectable levels of 1-2 ng/ml for 8 hours or more without any measurable signs of impairment in one-time users. In chronic users, detectable amounts of blood THC can persist for days. In one study of chronic users, residual THC was detected for 24 to 48 hours or longer at levels of 0.5 - 3.2 ng/ml in whole blood (1.0 - 6.4 ng/ml in serum)
This is ultimately going to make testing for impairment almost impossible to prove because of the variances in detected levels. Unlike alcohol where BAS levels are an accepted indicator of impairment levels, marijuana will likely be on the level of prescription drug detection, i.e. present but hard to tell their effects on impairment.
While your company is likely to update their drug and alcohol policies to specifically not allow smoking on the job or likely up to 24 hours before a job begins, proving impairment after an incident will be very difficult if not impossible.