Emergency War Surgery NATO Handbook: Part I: Types of Wounds and Injuries: Chapter V: Blast Injuries
United States Department of Defense
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Explosions inflict injury in a number of ways. Primary blast injury is due solely to the direct effect of the pressure wave on the body. Secondary blast injury results from penetrating or nonpenetrating damage caused by ordinance projectiles or secondary missiles, which are energized by the explosion and strike the victim. Tertiary blast injury results from whole body displacement and subsequent traumatic impact with environmental objects. Tertiary effects generally result from the bulk flow of gases away from an explosion and occur when the individual is in very close proximity to the explosion. Displacement may take place relatively far from the point of detonation if an individual is positioned in the path that gases must take to vent from a structure, such as in a hatch, in a doorway, or by a window. Thermal injury from radiation, hot gases, or fires started by the explosion are considered to be miscellaneous blast effects. Other indirect effects include crush injury from the collapse of structures and toxic effects from the inhalation of combustion gases.
The pressure wave close to the explosion moves outward at supersonic speed. As the wave spherically propagates, it decelerates and loses energy. In water, because of its incompressibility, the speed of wave propagation is much greater and the wave loses energy less quickly with distance. The lethal radius around an explosion in water is about three times the lethal radius of a similar explosion in air.
A typical pressure wave from an explosion in air is shown in Figure 17. Pressure rises almost instantaneously in the ambient environment and shell decays exponentially. The peak pressure and duration of the initial positive phase are a function of the size of the explosion and the distance from the detonation. In air, the peak pressure is proportional to the cube root of explosive weight and the inverse of the cube of the distance from detonation. If the pressure wave is in close apposition to a solid barrier, the pressure exerted at the reflecting surface may be many times that of the incident wave.
A blast wave that causes only modest primary injury in the open can be lethal if the casualty was caught near a reflecting surface such as a solid wall. The bulk flow of gases away from the explosion (blast wind) travels much slower than the shock wave, but may be of importance in causing displacement close to the point of explosion, especially with very large explosions.
For a sharp rising blast wave, damage to both inanimate and biological structures has been shown to be a function of the peak pressure and the duration of the initial positive phase (Figure 18). This figure illustrates the estimated blast levels necessary to cause a range of primary effects in man.
Figure 17
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