Erring on the side of cannabis caution in safety-sensitive workplaces

Canada is not the only country to legalize recreational marijuana. We now join company with South Africa, Georgia and Uruguay.

I do not have a personal issue with the legalization of marijuana; I think the police have been appropriately turning a blind eye to small amounts for personal consumption for years. It is as natural to this province as red cedar, the Pacific dogwood or the Steller’s jay.

The issue for employers is how to manage the interface of recreational drug use on the weekend or in the evening of a workday with fitness to perform in the workplace the next day. There are the competing rights of the freedom to consume a legal commodity on an employee’s own time and the obligation to show up for work fit and prepared to work efficiently and safely.

When it comes to alcohol, society has determined that a blood alcohol content (BAC) over 0.08% will result in an impaired driving charge, but a lesser amount of 0.05% will also have adverse implications including an administrative suspension of your driver’s licence for up to 30 days for repeat offenders within a five-year period. Typically, the threshold for a positive alcohol test in a safety-sensitive workplace is 0.04% BAC. The threshold for safety-sensitive workers is not a measure of impairment; it seeks instead to measure whether someone is “influenced” by alcohol.

The federal government has set the Criminal Code driving limits for tetrahydrocannabinol (THC) at two nanograms per millilitre (ng/ml), with an increased sanction at five ng/ml. It is worth noting that these limits are from plasma tests and do not translate readily to urine or oral fluid swab tests. Employers are unlikely to be drawing blood to conduct testing in the foreseeable future. 

Instead, workplaces typically use urine tests, which reveal THC metabolites. In other words, urine tests reveal the aftermath of THC having been metabolized by the body. Typical thresholds in a drug and alcohol policy for urine analysis is 50 ng/ml for the initial immunoassay test and 15 ng/ml for a laboratory analysis or gas chromatography/mass spectrometry test.

Oral fluid swab tests check for THC in the mouth. As with urine testing, there is a two-step process to a positive result: an initial threshold of four ng/ml, and then a final threshold of two ng/ml using more sophisticated testing methods. Like the thresholds with alcohol, these thresholds do not measure impairment but rather seek to measure whether someone is “influenced” by THC.

The advantage of oral fluid testing is that it will reveal recent use. The window of detection for occasional users is 12 hours, while chronic users show positive results up to 24 hours after consumption. While THC dissipates more slowly in oral fluid than it does in blood, it decreases rapidly in both following peak concentrations. Studies have indicated that THC concentration in blood can decrease by as much as 90% in 90 minutes.

All of the above begs the question of what a safe level of THC is for an employee in a safety-sensitive workplace. The metabolization of THC for each individual is not as predictable as it is with alcohol. Cognitive and psychomotor impairment is a significant risk associated with marijuana use, and it appears to be related to THC ingested and levels measured in blood or oral fluids. Timing and duration of impairment is variable but can last for a long time depending on many factors. Accordingly, there is arguably no safe level of THC for those working in a safety-sensitive environment.

I understand that Air Canada and WestJet prohibit employees in safety-sensitive positions from using marijuana. Many police departments have imposed the same standard, while the RCMP has proclaimed a 28-day limit. Other first responders, including the West Vancouver Police Department and the military, have imposed a 24-hour ban on marijuana consumption prior to active service.

Impairment is a critical issue in a safety-sensitive environment because a minor performance flaw may result in serious injury or death.

It is also important to note that, unlike with alcohol, self-assessment of impairment from THC is unreliable. Cognitive effects will persist after the more obvious euphoric or tranquil effects of THC have subsided.

Measuring impairment from THC is a vexing problem because there are many variables such as the quality of the product, method of consumption and individual tolerances. But given the importance of safety in the workplace, adjudicators and society generally need to recognize that while the measurement of whether someone is “influenced” may not be precise in every case, it is the only available tool to manage a significant safety risk. Let’s all be responsible and be safe. •

Gregory J. Heywood is a founding partner at Roper Greyell, where he provides strategic and practical advice to employers on labour and employment issues in the workplace.