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Brisance is the shattering capability of a high explosive, determined mainly by its detonation pressure. The term can be traced from the French verb "briser" (to break or shatter) ultimately derived from the Celtic word "brissim" (to break). Brisance is of practical importance for determining the effectiveness of an explosion in fragmenting shells, bomb casings, grenades, structures, and the like. The sand crush test and trauzl lead block test are commonly used to determine the relative brisance in comparison to TNT (which is considered a standard reference for many purposes).
Fragmentation occurs by the action of the transmitted shock wave, the strength of which depends on the detonation pressure of the explosive. Generally, the higher this pressure, the finer the fragments generated. High detonation pressure correlates with high detonation velocity, the speed at which the detonation wave propagates through the explosive, but not necessarily with the explosive's total energy (or work capacity), some of which may be released after passage of the detonation wave. A more brisant explosive, therefore, projects smaller fragments but not necessarily at a higher velocity than a less brisant one.
One of the most brisant of the conventional explosives is cyclotrimethylene trinitramine (also known as RDX or Hexogen). RDX is the explosive agent in the plastic explosive commonly known as C-4, comprising 91% of it by mass.