In non-occupational asbestos exposure cases where the incremental risk above background exposure is negligible (relative risk of approximately 1.004 to 1.006), causation is not established on the balance of probabilities. The plaintiff bears the burden of proving that the specific exposures caused or materially contributed to the disease; the defendant is not required to prove that the exposures did not cause the disease. There is no rational basis for distinguishing between 'bystander' and 'handyman' exposure for duty of care purposes; the relevant distinction is between occupational and non-occupational exposure. Expert evidence that treats any increment in risk, however small, as causative is insufficient to discharge the plaintiff's burden of proof without an assessment of the relative magnitudes of the specific exposure risk and the background risk.
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