Explosives are materials that are rapidly converted into gases when detonated. Blast and blast injury are, respectively, general terms used to describe this gaseous decomposition and the damage occurring in an organism subjected to the pressure field produced by an explosion.
Blasts are characterized by the release of large quantities of energy in the form of pressure and heat, with the exact amount depending on the type and amount of explosive. If the explosion is confined within some sort of casing (e.g., a bomb), the pressure will rupture the housing and eject the resulting fragments at high velocity. The remaining energy is transmitted to the surrounding environment in the form of a blast wave, blast winds, ground shock, and fire.
The blast wave begins as a single pulse of increased pressure that rises to peak levels within a few milliseconds and then rapidly falls to a minimum pressure that is lower than the original atmospheric pressure (Fig 192-2). It is propagated outward radially from the explosion, with the sharply marginated periphery of the sphere becoming the blast, overpressure, or shock wave, as it has been variously called. The duration and level of the high-pressure peak depends on the nature of the explosive, the conducting medium, and the distance from the detonation point. This blast wave pressure peak determines the overpressure that an object in its path is subjected to and is the main determinant of primary blast injury. Conversely, the negative pressure wave, or suction of the blast wave, lasts several times longer than the high-pressure wave but can never be greater than -760 mmHg (-14.7 psi). Representative pressure effects are listed in Table 1...9.2.-.7.
FIG. 192-2. The general form of a blast wave. (From Stapczynski JS: Blast injuries, in Edlich RF, Spyker DA (eds): Current Emergency Therapy '85. Rockville, MD, Aspen Systems Corporation, 1985, p 294.)
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