A critical injury means an injury of a serious nature that...

• places life in jeopardy,
• produces unconsciousness,
• results in substantial loss of blood,
• involves the fracture of an arm or a leg 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.

Source:
Occupational Health and Safety Act of Ontario, Regulation 834.