Blast injuries result from explosive detonation and are classified into four categories based on mechanism. The NP must understand blast physics to anticipate injury patterns. Primary blast injury results from the blast overpressure wave (a supersonic pressure front traveling outward from the explosion). This wave causes tissue damage at air-fluid interfaces where impedance mismatch causes differential tissue acceleration: lungs (blast lung — the most common fatal primary blast injury), tympanic membranes (most sensitive indicator — ruptured TM suggests significant blast exposure), bowel (mesenteric hemorrhage, delayed perforation days after exposure), and eyes (globe rupture, retinal detachment). The overpressure wave causes alveolar hemorrhage, pneumothorax, and air embolism in the lungs through a mechanism of spalling (tissue fragmentation at density interfaces), implosion (gas-filled spaces collapse then rebound), and inertial shearing (tissues of different densities accelerate at different rates). Secondary blast injury results from projectile fragments (shrapnel, debris, glass, nails in improvised explosive devices) propelled by the blast. This is the most common cause of blast-related injury and death. Injuries mimic penetrating trauma: lacerations, fractures, foreign body embedment, vascular injury. Tertiary blast injury results...