- Any injury arising from the application of mechanical energy. Other agents (heat, electricity, laser radiation, plasmas, etc.) have additional effects, which I will discuss in a later article in this series.
- When objects collide with each other, their kinetic energy is dissipated in several ways - sound waves, heat, and deformation or disruption of the objects' internal structure. It is this deformation which leads to tissue damage. The more dense the tissue, the greater resistance it offers and thus the damaged sustained is worse.
Example Tissue Densities
Tissue Density (g/cc) Lung 0.4 Fat 0.8 Muscle and solid organs 1.0 Skin 1.05 Bone 1.11 to 1.4
Ballistic and Penetrating Trauma
There are three primary mechanisms of injury caused by projectiles.
- Crushing/laceration - the missile track through the target.
- Cavitation - pressure waves generated by medium and high velocity missiles (see definition below) disrupt tissues remote from the projectile's path. The missile track can also be widened by tumbling bullets.
- Fragmentation - primary - pieces of missile ; secondary - anatomical structures that are shattered and displaced.
Different ammunition types have different energy transfer characteristics. Armour-piercing rounds transfer a lesser percentage of their energy to a target (blowthrough), while hollow points, fletchettes and shot are designed to transfer nearly all their kinetic energy into a target.
|Ammunition Type||Damage Multiplier|
|HEAP||0.5 * velocity component of energy|
|Damage is sustained only if armour is breached, unless armour is flexible ; see blunt trauma, below.|
|The speed of sound is about 1115ft/s (340.3m/s) at sea level at one atmosphere pressure and 15 degrees Celsius.|
|Low velocity||< 1000 ft/s
|Medium velocity||1000-2500 ft/s
(304.8 to 762 m/s)
|High Velocity||>2500 ft/s
|Cavitation and fragmentation effects
predominate at higher energies (medium to high velocity).
Hypervelocity missiles produce crater-like wounds. The differences between blast injuries and high velocity missile injury decrease with increased missile energy.
|Muzzle abrasion||point blank|
|Gases present in victim's clothing, etc||1 - 3 in. (2 - 7.6 cm)|
|Burned powder grains, soot||1 - 3 in. (2 - 7.6 cm)|
|Unburned powder grains||1 - 2 ft. (30 - 60 cm)|
|Tattooing and abrasions ensue from the above.|
|Metal fragments (bullet, primer)||< 6 ft. (1.8 m)|
Shotguns: As above, plus
|Single entry wound||< 79 in. (2 m)|
|Wound less than 1" in diameter||< 18 in. (45.7 cm)|
|Wadding in wound||79 - 236 in. (2 - 6 m)|
|Entry wounds will be clean holes beyond about 2 m, except with close range shotgun and hypervelocity missile wounds, which are almost indistinguishable from blast (massive tissue destruction). Exit wounds are usually irregular without an abraded perimeter.|
A blade is sharp because the edge (tip) has a very small surface area. The force applied in cutting may be small, but the pressure at the points of contact is enormous (pressure = force/area), so the surface being cut yields. (Note that while ballistic cloth will stop bullets, it doesn't stop blades without special reinforcement eg. mesh underlay or ceramic/metal inserts).
Forensic aside : Stab wounds (depth > width) or incisions (cuts, width > depth) look different from chopping wounds. All such injuries are well demarcated with sharp edges. Nerves and blood vessels may bridge a chop wound (higher tensile strength than skin) ; they will not be present in a stab wound or cut.
Consider the occupant of a motor vehicle. Energy transfer to vehicle occupants is enormous: At 55mph (88.5km/h or 24.6m/s), a 180lb (81.6kg) person has a kinetic energy (0.5 * mass * velocity^2) of (0.5 * 81.6 * (24.6)^2) or 24690J - more than the muzzle energy of a .50 machine gun round! This is dissipated very rapidly in a collision.
Injury is sustained because of the development of pressure waves radiating from the points of impact through the victim.
Some key structures (e.g., the aorta, portal vein, spinal cord, and oesophagus) will resonate and rupture, with enough energy. Bone shatters.
|Trauma and Lethality at Velocity|
|Velocity (m/s)||% blunt trauma/fracture||% lethality|
Assumes impact with a relatively rigid surface. (Real World data, TL 7-8)
Flexible armour offers some protection, but some energy will be transmitted to the target (e.g., the extensive bruising+ sustained when one is shot in a Kevlar-protected area). To simulate this effect in Traveller combat, treat roughly as per T4 : one point of damage per die penetrates flexible armour.
Forensic aspects : Lacerations occur when enough blunt force has been applied to disrupt the skin. They are typically irregular in outline with edge abrasions. Nerves and vessels may bridge wound. Abrasions are usually secondary to being dragged. Skin tags usually identify the direction of dragging. A yellowing bruise is at least two days old. Bruising must be differentiated from lividity (caused by dependent pooling of blood in the recently deceased) and marbling (which is due to bacterial action on blood pigments and doesn't appear for two to three days after death).
Explosion injuries can be considered to be a mixture of blunt (blast overpressure) and penetrating (fragment) trauma. Variables that influence blast damage include confinement (e.g., small room, strong walls) and the distance from the explosion (inversely as the square of the distance), in addition to the energy released. Air-containing tissues are quite susceptible to injury. Lung damage and eardrum rupture require relatively little overpressure to produce. The human body is surprisingly robust, however.
|Peak Overpressure (kPa)||Effects|
|3 to 7||Window glass shatters|
|10 to 38||Concrete shatters|
|20 to 60||Brick shears apart|
|> 69||Lung damage will occur|
|90 to 130||50% chance of eardrum rupture|
|160 to 230||1% chance of death|
|230 to 400||50% chance of death|
|400+||100% chance of death|
|One atmosphere = 101.3kPa, 7kPa ~1
kPa = kilopascal or 1000 pascals. One pascal is equal to one newton of force applied over an area of one square metre.