APPENDIX A: WEAPON EFFECTS

Military munitions and firearms produce injuries not commonly seen in civilian trauma. Weapon types can be roughly divided into two major subtypes: small arms fire and explosive munitions. Small arms fire is typically from hand guns and assault rifles.1

When a small arms projectile hits tissue, it produces two types of injuries: a permanent cavity and a temporary cavity. The permanent cavity is the tissue destroyed by the actual pathway of the projectile. Military rounds are designed to turn, or yaw, upon contacting tissue. As the bullet turns, the permanent cavity size increases. This is evidenced by small entry wounds and large exit wounds. A second, temporary cavity occurs from a pressure wave created by the high-velocity round. Elastic, and inelastic tissue, is put under stress which manifests as delayed necrosis and is one of the reasons we do not advocate for wound closure following the initial debridement. The degree of damage is proportional to a projectile’s kinetic energy and more specifically its velocity (Kinetic Energy = ½ (Mass) x Velocity). Particles distributed by blast explosions also create permanent and temporary cavities.

Explosive munitions injure through four major mechanisms. The number of mechanisms a person is exposed to depends on their distance from the explosion, with persons closer to blasts being exposed to more mechanisms of injury. (See Figure 2 below.) Primary blast injuries occur from a pressure wave known as a blast wave. The blast wave can sheer off tissue, damage solid organs, and damage hollow viscus injuries from pressure changes in the air contained within the organs. These injuries may manifest several days after the blast and are typically discovered on serial examinations of the injured patient. Secondary blast injuries are penetrating injuries which result from particles contained within the munition or from debris from the surrounding environment distributed by the blast. Tertiary blast injuries comprise two subtypes of injury. The first is a negative pressure wave called a blast wind which follows the positive pressure of a blast wave. Similar injuries are produced by both blast wind and blast waves. The second subtype of injury is blunt trauma resulting from large objects being projected into a body, or a person’s body being projected into the surrounding environment, like a wall or the ground. When a blast hits a vehicle, occupants are susceptible to being injured by sequential pressure waves as they reflect around the inside of the vehicle. Quaternary blast injuries also comprise two major subtypes. The first subtype is burn injuries, which are treated as outlined in the JTS Burn Care Clinical Practice Guideline. The second are CBRNE injuries (Chemical, Biological, Radiological, Nuclear, and Environmental Injuries) and are managed as outlined in CBRNE guidelines.

Virtually every organ is susceptible to injury from blast explosions and many of these injuries, particularly hollow viscus injuries and soft tissue necrosis, present in a delayed format, necessitating serial exams and clinical awareness.

Reference: Cubano, M.A., et. al. Chapter 1: Wespons Effects and War Wounds. Emergency War Surgery, 5th United States Revision. Fort Sam Houston, TX: Borden Institute, 2018.