It depends which regulator you're reporting to — the Ministry and WSIB run on different clocks, and an injury can trigger both at once.
Short answer
If the injury is critical, the employer must immediately notify the Ministry's Health and Safety Contact Centre, then deliver a written report within 48 hours to the Ministry, the joint health and safety committee or representative, and the union. Separately, for WSIB purposes, “we must receive your completed accident report within three business days after your reporting obligation begins,” which starts once a worker needs health-care treatment, loses time from work, earns less than regular pay, or requires modified work at regular pay for more than seven calendar days. The two obligations run independently, and a single serious injury can trigger both.
This clock only starts for injuries that meet the statutory definition of critical injury or a fatality. It's immediate notification by phone or the contact centre, then a written report inside 48 hours — there's no cost or duration threshold here, only the injury classification. A minor sprain never triggers this track no matter how much work time it costs.
This clock is about consequence, not classification. It's triggered by health-care treatment, time away from work, reduced earnings, or extended modified duty — specifically, “if your employee requires modified work for more than seven calendar days at regular pay, we must receive your Employer's report of injury (Form 7) within three business days of the eighth calendar day of modified work.” First aid alone, with no time off and no pay impact, doesn't start this clock at all. A badly sprained ankle that needed a walk-in clinic visit can trigger the WSIB track while never coming close to the critical-injury definition that triggers the Ministry track.
A worker fractures a wrist in a fall. Because a wrist fracture is treated as an arm fracture under the critical injury definition, the Ministry track starts immediately — contact centre notification now, written report within 48 hours. Separately, the worker needs treatment and is off work, so the reporting obligation to WSIB also begins, with Form 7 due within three business days of that obligation starting. Missing either deadline is a separate compliance failure; meeting one doesn't excuse the other.
WSIB and the Ministry's Health and Safety Contact Centre are Ontario-specific; WorkSafeBC and every other provincial workers' compensation board set their own claim-reporting deadlines under their own legislation. If you operate outside Ontario, confirm the specific day count with that province's board rather than assuming the three-business-day WSIB clock applies.
A 30-minute call is enough to tell you whether your incident-response checklist actually separates the two tracks.
