The timing of psychological symptoms after a workplace incident can raise a serious question about causation, but timing alone won't answer it. In Decision No. 974/07, 2008 ONWSIAT 625, the Ontario Workplace Safety and Insurance Appeals Tribunal considered whether a worker's later psychological disability resulted from a chemical exposure at work.
The exposure caused short term physical changes. The worker subsequently experienced significant psychological symptoms and challenged the Board's decision denying compensation for psychotraumatic disability.
A medical assessor appointed for the Tribunal concluded that the worker was already developing a depressive illness around the time of the exposure. The panel accepted that opinion. It found the later severe symptoms were manifestations of the depressive illness rather than consequences of the chemical exposure, and that the illness would have developed in any event.
The appeal was dismissed. Importantly, the decision didn't deny that the worker experienced real psychological symptoms. The question was whether those symptoms met the required connection to the compensable workplace incident. The Tribunal resolved that issue against the worker on the medical evidence before it.
This is a narrow, evidence dependent result. It shouldn't be read as a general statement that psychological conditions arising near a workplace event are unrelated to work. It illustrates the need to distinguish the existence and seriousness of a condition from proof of the cause that makes it compensable.
Source note: This account uses the WSIAT's official published counsel summary. The full historical reasons weren't available through the tribunal's legacy PDF link.