"A negative modifier can’t reduce damage below 0 if the attack does crushing damage, or below 1 if it does any other type of damage." 
Damage Types Based on Attack Edit
- Burning Attack (burn): fire damage, and more rarely, ice damage (without incendiary (inc) effect). If you're wondering if things catch fire, see Making Things Burn
- Corrosion Attack (cor): Acid and alkaline effects, capable of reducing DR over time.
- Crushing Attack (cr):
- Cutting Attack (cut):
- Fatigue Attack (fat):
- Impaling Attack (imp):
- Piercing Attack
- Small Piercing Attack (pi-); Normal Piercing Attack (pi); Large Piercing Attack (pi+); Huge Piercing Attack (pi++)
- Toxic Attack (tox): An attack that causes actual cellular damage,. Doesn't apply to most Unliving creatures, and in most cases is avoided with Resistance or Immunity to Metabolic Hazards.
Wounding Modifiers and InjuryEdit
Any damage that gets through DR is modified by type
- Small piercing (pi-): x0.5.
- Burning (burn), corrosion (cor), crushing (cr), fatigue (fat), piercing (pi), and toxic (tox): x1 (damage is unchanged).
- Cutting (cut) and large piercing (pi+): x1.5.
- Impaling (imp) and huge piercing (pi++): x2.
The damage after this multiplier determines the injury: the HP lost by the target. Round fractions down, but the minimum injury is 1 HP for any attack that penetrates DR at all. General description of each type of damage is provided under Innate Attack.
Damage Modifiers are a series of special enhancements and limitations on an attack. While they can be used for any attack form it is most common with Affliction as demonstrated by the utterly huge number of examples in the books.
Putting it togetherEdit
Here a few examples of how all this comes together, Other examples are under the relevant main damage type.
- Particle Beam (+300%): Burning Attack 2d+2 (Accurate +2, +10%; Armor Divisor (5), +150%; Increased 1/2D, x10, +15%; Increased Max, x2, +5%; Radiation (rad), +100%; Surge, +20%) 
- Pestilence (+1,560%): Fatigue Attack 1 point (Based on HT, +20%; Costs Fatigue, 6 FP, -30%; Cyclic, 1 hour, 72 cycles, Highly Contagious, +1,470%; Malediction 1, +100%; No Signature, +20%; Onset, 1 hour, -20%) 
- Rain of Stones (+100%): Crushing Attack 5d (Area Effect, 2 yards, +50%; Blockable, -5%; Bombardment, skill 10, -15%; Overhead, +30%; Persistent, +40%) 
- Tranquilizer Dart (-35%/+210%): Small Piercing Attack 1d (Accurate +1, +5%; Armor Divisor (0.2), -50%; Increased 1/2D, x5, +10%)  + Affliction 1 (HT; Follow-Up, Small Piercing Attack, +10%; Unconsciousness, +200%)  Total 
"You take half *damage.* Damage is the roll before DR. "Half injury" would be after DR." http://www.sjgames.com/gurps/faq/FAQ4-5.html
- Kromm http://forums.sjgames.com/showpost.php?p=75800&postcount=22 on damage bonuses from different combat skills not stacking