Number and risk of first-aid visits and serious incidents associated with using different substances individually.

For each substance, the risk of visiting a first aid station was calculated by dividing the number of first aid visits (FAVs) related to that substance by the number of FAVs for that cohort.CI = 95% confidence interval. Confidence interval for relative risk (RR) of a serious incident (SI) was calculated using Morris and Gardner's [46] formula.The category no substance is the reference category for the SI risk ratios.