Objectives In 2003 British Columbia’s occupational health and safety (OHS) regulator implemented a voluntary audit-based OHS recognition program in select industrial sectors. Firms achieving OHS certification received a rebate on workers’ compensation premiums. This study evaluated the effect of OHS certification on firm work-injury rates for the years 2004 to 2011.

Method A cohort of certified (intervention) and non-certified (control) firms was derived from workers’ compensation claims records from 2000 to 2011. Firms were drawn from the industrial sectors covered by the OHS program and had to have paid workers’ compensation premiums for at least three years during the study period. A difference-in-difference evaluation approach using random-effects Poisson regression was implemented that accounted for the difference in baseline injury risk and the change in injury risk over time between the intervention and control group. Estimates were adjusted for industrial sector, firm size, firm tenure and industrial sector average injury risk. Outcomes investigated were loss-time injuries and a subset of more serious work injuries.

Results The intervention group included 4392 firms who achieved OHS certification between 2003 and 2010. These firms had similar baseline loss-time (IRR: 1.04 95% CI: 1.00–1.08) and serious injury rates (IRR: 0.99 95% CI: 0.94–1.04) compared to controls. Safety certification was associated with a decline in the loss-time (IRR: 0.92 95% CI: 0.90–0.94) and serious injury rate (IRR: 0.88 95% CI: 0.85–0.92).

Conclusions Voluntary audit-based OHS certification was associated with a 8% and 12% reduction in loss-time and serious injuries British Columbia between 2004 and 2011.