The severity of injury inflicted by a missile is determined by the structure hit and retardation of the missile and thus the energy dissipated to the tissue. The injury to tissue depends on the kinetic energy and the construction of the missile, and the density and resilience of the tissue. Devastating, heavily contaminated wounds are inflicted by close-range shotguns and high-energy missiles, and thorough wound debridement and delayed primary closure are required after about four days. In general, it is not necessary to remove the missile unless this can be done easily. Explosions in air can cause burns, shrapnel wounds, acceleration and deceleration injuries. The shock wave dissipates energy on the border between air and fluid. This injuries primarily hollow organs such as lungs and intestines. Casualties from blasts may exhibit no external symptoms or signs of lung or intraabdominal injury. It is necessary to perform serial physical examinations, blood gas analyses, chest X-ray or CT scan.