Tests showed worker had double the concentration limit permitted by workplace policy
“An arbitrator is going to need evidence of impairment to uphold termination for a failed post-incident drug test, so when incidents happen, the people observing must ask questions about whether there are any signs of impairment - and you may need expert evidence on impairment.”
So says Jackie Laviolette, a labour and employment lawyer at Mathews Dinsdale in Calgary, after an arbitrator overturned an Alberta worker’s termination for a post-incident drug test.
CST Canada Coal operates a coal mine near Grande Cache, Alta. The worker joined CST as a heavy equipment operator in November 2022, driving haul trucks - massive trucks capable of hauling up to 100 tons of coal and rock. The mine had many steep ramps upon which trucks had to travel.
Given the dangerous nature of the coal mine, CST had a drug and alcohol policy requiring employees to report fit to work and without an alcohol or drug level in their system above the concentration limits specified. For THC – the psychoactive element in cannabis - the policy set a cut-off limit of two nanograms per millilitre (ng/ml) in oral fluid drug tests. The policy stated that a positive drug or alcohol test “may be just cause for termination.”
The concentration limits were based upon the “Canadian Model for Providing a Safe Workplace,” and standards created by the Construction Owners Association of Alberta. It was reviewed with the worker during his orientation and annually during safety meetings, and the worker was also on the joint health and safety committee.
Cannabis consumption
On March 5, 2024, the worker had a day off. He ate two cannabis gummies, followed by sharing a marijuana joint with a friend around 6 or 7 p.m. Twelve hours later, at 6:15 a.m. on March 6, he reported for work.
There were no incidents that day, but the following day the worker was driving a haul truck down a steep ramp when the truck downshifted and the tires locked, causing it to skid down the ramp. The worker tried unsuccessfully to unlock the brakes and then steered into a berm on the side of the road to stop the truck, spinning it around.
Nobody was hurt and there was no damage, but a supervisor determined that there had been a high potential for injury and loss of life. He sent the worker for a post-incident drug and alcohol test involving an oral fluid sample. The worker was suspended with pay pending the results of the test, but he didn’t show any signs of impairment. A safety supervisor drove him home, during which the worker said he smoked marijuana on his days off but he didn’t think he would test positive.
The test results showed that the worker had four ng/ml of THC in his system, double the concentration limit allowed by the drug and alcohol policy. On March 20, CST terminated the worker’s employment for violating the policy by reporting for work with THC levels above the cut-off limit. At the termination meeting, the worker said he didn’t have a substance abuse problem but he used marijuana on his days off.
The union grieved, asserting that the worker wasn’t impaired at work so there wasn’t just cause for termination. It argued that the test didn’t prove impairment and there was no evidence of impairment, and the policy wasn’t clear enough to employees that they could be disciplined for consuming cannabis on their days off – the worker said he didn’t understand what the limits in the policy meant, as they were “just numbers to him.”
Fit for work
CST countered that its drug and alcohol policy, based on industry standards, was clear and consistently enforced, requiring employees to report “fit for work” and not exceed specified drug or alcohol levels. The company emphasized the policy’s importance in maintaining safety at the mine.
The arbitrator found that the worker breached the policy by attending work with THC levels exceeding the prescribed limits, but determined that termination wasn’t justified.
The arbitrator noted that it the jurisprudence had established that a positive test for THC doesn’t prove impairment, nor does a specific amount, such as four ng/ml in the worker’s case, prove anything without expert evidence. In addition, there were no observations at the time of the incident that the worker showed any signs of impairment, the arbitrator said in finding that CST hadn’t established that the worker was impaired.
“[CST] made the argument that [the worker] was over the limit in the policy and therefore the burden shifts to the union to claim that he wasn’t impaired, but [the arbitrator said] if you're going to claim termination for violation of the policy, you're going to need that impairment component,” says Laviolette. “With a lack of any evidence of impairment, [the arbitrator] found that termination was excessive - but he did say that had that evidence been there, he probably would have upheld the termination.”
The arbitrator also found that the policy established two distinct responsibilities for employees – they must be fit for work and not impaired when they report, and they must not report for work with an alcohol or drug level equal to or in excess of the stated concentration limits. Although the limits didn’t prove impairment, they indicated when there was a heightened risk of impairment and were therefore reasonable, said the arbitrator, adding that the policy was clear on the potential consequences of exceeding the limits in a test.
“You can put a limit in your policy, but the second question will be on how just beating the number isn’t going to be enough to get you all the way to termination without this piece around illustrating impairment,” says Laviolette. “It goes back to the purpose of the policy, which is to make sure that people are fit to be at work and are operating in a safe manner - without evidence around impairment, you essentially aren't illustrating that.”
Just cause for discipline
The arbitrator also agreed with CST that the worker was aware of the concentration limits and that his conduct in consuming cannabis so soon before a shift was “reckless.” As a result, discipline for breaching the policy was justified, the arbitrator said.
However, the arbitrator found that CST had a role as the employer to explain to employees what the concentration limits meant from a practical perspective. The Canadian Model for Providing a Safe Workplace – from which the limits were taken - states that “education and awareness are considered to be the principal methods of gaining commitment to and compliance with these guidelines,” said the arbitrator.
Although CST reinforced the policy annually to employees, broader education about what the limits meant in terms of practical consumption would both strengthen compliance and reduce safety risks, the arbitrator said, adding that a lack of employee education on the risks of off-duty cannabis use could inadvertently result in exceeding the policy’s limits. Combined with the fact that the worker was a good employee with no prior discipline, termination was excessive, the arbitrator said.
“The policy was valid and the employer met the KVP test [for a reasonable policy and the worker’s awareness of it], but this secondary step of educating them on, essentially, the use of cannabis goes a bit further than what would be required at law,” says Laviolette. “That being said, it would be good practice, because it takes away the argument that the worker didn’t know - it's a pretty common response when you get to arbitration.”
Reinstatement not appropriate
However, the arbitrator determined that reinstatement was inappropriate due to the breakdown of trust necessary in a safety-critical environment. Instead, the arbitrator ordered CST to provide compensation in lieu of reinstatement, directing the parties to discuss the appropriate amount.
In light of this decision, an employer would be smart to ensure that education on all the elements of a drug and alcohol policy is available, according to Laviolette.
“If you end up in a grievance over a failed drug and alcohol test - especially before this arbitrator - this case is going to be pulled out and they're going to say, ‘What did you do in relation to education?’” she says. “You'd be well-advised to do it, but do you legally have to? I'm not sure that you do.”
Despite the fact that the termination wasn’t upheld, the strength of CST’s policy and that it followed it contributed to a positive result for the employer, says Laviolette.
“Looking at how they wrote that policy and at the post-incident testing, that’s another win for employers being able to make that decision of who you want in your workplace,” she says. “They weren't successful in upholding the termination, but they took the action they thought was appropriate to protect their workforce and, ultimately, he's not in the workplace anymore imposing risk to anybody or the workplace itself - to me, that's a win [for the employer].”
See CST Canada Coal Ltd. and UMWA, Local 2009 (Blignault), Re, 2025 CarswellAlta 13.
