Some substances are more toxic than others. The toxicity of a substance is described by the types of effects it causes and its potency. 1  Types of Effects: Different chemicals cause different effects.
I think I remember reading that injured means bruises and lascerations, seriously injured meant hospital but not life threatening, critically injured meant hospital ICU time and fatally injured meant injuries leading to dying sometime later.
The definition of critical injury is any serious injury that places the person's life at risk, results in unconsciousness, results in significant loss of blood, results in the fracturing of a major bone, results in leg or arm amputation, results in permanent blindness, results in burns to over 50% of the body.