It's a closed list, not a judgment call you make on site. Ontario's O. Reg. 420/21 defines critical injury by naming exactly which outcomes qualify — nothing more, nothing less.
Short answer
A critical injury is one that “places life in jeopardy; produces unconsciousness; results in substantial loss of blood; involves the fracture of a leg or arm, but not a finger or toe; involves the amputation of a leg, arm, hand or foot but not a finger or toe; consists of burns to a major portion of the body; or causes the loss of sight in an eye.” If the injury matches one of these, the reporting and scene-preservation obligations apply immediately, regardless of how it happened.
The finger-and-toe carve-out is the one that trips people up: a broken forearm is critical, a broken finger on its own is not. But the Ministry's own interpretation widens the anatomy on the other side — “leg” includes the ankle or foot and “arm” includes the wrist or hand, and a fracture or amputation involving more than one finger or toe is treated as critical even though a single digit isn't. So a crushed hand with two broken fingers clears the bar; a single broken finger doesn't, on its own.
A critical injury or a fatality triggers the same response: immediate notification to the Ministry's Health and Safety Contact Centre, the joint health and safety committee or representative, and the union, followed by a written report within 48 hours, plus the scene-preservation duty covered in must you preserve the accident scene. An injury that's serious but doesn't match the list — a sprain, a laceration requiring stitches, a single fractured toe — still has to be logged and may still trigger a WSIB report, but it doesn't pull the same immediate-notification and scene-preservation machinery; see when you must report an injury for how the two tracks diverge.
Under-calling a critical injury — treating a two-finger fracture as routine because “it's just fingers” — means the Ministry, JHSC and union never get the immediate notification the Act requires, and the scene may already be disturbed by the time anyone realizes the mistake. Over-calling isn't free either: it triggers scene preservation and a Ministry response for an injury that doesn't meet the definition, which slows the site down for no regulatory reason. The fix is the same either way — check the injury against the actual list rather than against how serious it looks.
The definition itself only decides whether an incident is critical; it doesn't decide who's responsible for the notification or what happens to the scene in the meantime. See critical injury reporting for the fuller notification chain, and who counts as the constructor on your job for who actually carries the notification duty when more than one employer is on site.
A 30-minute call is enough to tell you whether your site supervisors could apply this list correctly under pressure.
