The Right to Be Wrong: Supreme Court of Canada Lowers the Causation Bar on Occupational Disease and Injury

22 juillet 2016 | Eric Ito

( Disponible en anglais seulement )

On June 24, 2016, the Supreme Court of Canada provided considerable latitude to decision makers regarding occupational disease and injury in British Columbia (Workers’ Compensation Appeal Tribunal) v. Fraser Health Authority (“Fraser Health”).

Fraser Health concerned three technicians at a hospital laboratory who were diagnosed with breast cancer. The workers made a claim under the B.C. Workers Compensation Act on the basis that their cancer was an occupational disease. During the process, WorkSafeBC considered three expert reports. One report was prepared by the Occupational Health and Safety Agency for Health Care in British Columbia regarding the incidence of cancer in the laboratory where the workers were employed. The other two reports were prepared by doctors specializing in occupational medicine.

Each of the reports’ conclusions were substantially similar: the experts were unable to conclude there was a definitive link between the technicians’ jobs and their disease. As a result, WorkSafeBC denied the claims.

The technicians appealed to the Workers’ Compensation Appeal Tribunal (“WCAT”) and were successful. WCAT found that while the expert reports could not conclusively link the  workers’ cancer to their jobs, this would not preclude a successful claim. Compensation for occupational diseases requires the application of a lower standard than scientific certainty: as long as there is some “positive evidence” to suggest a link between a worker’s disease and his or her employment, this is sufficient. Applying that principle to the facts, WCAT noted two kinds of positive evidence:

  • the disproportionate rate of cancer among the technicians (eight times the average of the general population); and
  • the closeness in time between the workers’ employment and the onset of their disease.

Taken together, WCAT held these facts were enough for it to draw a “common sense” inference that the workers’ employment caused the cancer. WCAT held that the technicians were eligible for compensation.

The Supreme Court of British Columbia reviewed the WCAT decision. The Court noted that in these instances, under the B.C. Administrative Tribunals Act, the standard of review to be applied is whether the WCAT decision was “patently unreasonable”. The Court found there was no evidence capable of supporting WCAT’s conclusion that the workers’ employment caused the cancer. WCAT ignored the expert evidence in favour of its own expertise and its decision was therefore patently unreasonable. The Court set aside the decision and remitted the matter back to WCAT.

The B.C. Court of Appeal denied the workers’ appeal and the matter came before the Supreme Court of Canada (“SCC”). The SCC focused on two major issues at the heart of the case. The first was the applicable standard of review: “patent unreasonableness.” This standard, the SCC held, means that a tribunal’s decision should be overturned only when there is no evidence capable of supporting it. In other words, as long as the decision falls within a range of possible outcomes, a court should let it stand.  

The second issue was whether WCAT’s decision was patently unreasonable. In order to make this determination, the SCC considered the standard of causation in occupational disease cases. In B.C., a worker’s employment need only be of some “causative significance” or “more than a trivial or insignificant aspect” in the development of the disease. In other words, the employment does not need to be the cause of the disease, but only a cause. Although the expert reports were inconclusive, they did not rule out the possibility of a link between the cancer and the employment. As WCAT noted, the cancer rate among the workers was statistically higher than the average, and the closeness in time between the workers’ employment and their diagnoses suggested it was possible that their employment caused the disease. The WCAT decision fell within a range of possible outcomes and thus the decision could not be considered patently unreasonable. The workers’ appeal was successful and the WCAT decision was restored.


In order to be compensable in B.C., a worker only needs to demonstrate that her or his employment was more than a trivial aspect of the injury or disease and where the evidence weighs evenly, the law requires WorkSafeBC to rule in favour of the worker. While this is not new, the SCC appears to have expanded that principle to allow WCAT to draw its own “common sense” inferences in the absence of scientific proof. This is surprising given the vital role that expert medical evidence has traditionally played in workers’ compensation decisions. This case also serves as an important reminder of the very high level of deference afforded to administrative tribunals by courts, which one judge described as “the right to be wrong.”   

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