If a type of accident is usually going to cause horrible pain if it causes death, this creates a bigger incentive to avoid serious injury in the first place (which also helps avoid death from those injuries).
If suffering is taken into account for injury, also taking it into account for death avoids situations where it would be preferable for the perpetrator to cause death rather than have the victim survive in pain. There's no threshold because the fatality is considered in addition to rather than instead of the suffering.
If a type of accident is usually going to cause horrible pain if it causes death, this creates a bigger incentive to avoid serious injury in the first place (which also helps avoid death from those injuries).
If suffering is taken into account for injury, also taking it into account for death avoids situations where it would be preferable for the perpetrator to cause death rather than have the victim survive in pain. There's no threshold because the fatality is considered in addition to rather than instead of the suffering.