II.

Characteristics of Explosives

Explosives are grouped into two main classes, low explosives, which burn at rates of inches per second, and high explosives, which undergo detonation at rates of from 914 to 9140 m per sec (1000 to 10,000 yd per sec). Explosives vary in other important characteristics that influence their use in specific applications. Among these characteristics are the ease with which they can be detonated and their stability to conditions of heat, cold, and humidity. The shattering effect, or brisance, of an explosive depends upon the velocity of detonation. Some of the newer high explosives with a detonation rate of 9140 m per sec are extremely effective for military demolition and certain types of blasting. On the other hand, for quarrying and mining, when it is desirable to dislodge large pieces of rock or ore, explosives with a lower detonation velocity and lower brisance must be employed. Explosives used as propellants in rifles and cannon should burn still more slowly, as they are required to deliver a steadily increasing push to the projectile in the barrel of the gun rather than a sudden shock which, if strong enough, might break the gun. Special types of explosives that are sensitive to heat or shock and have a medium-high brisance are used to initiate the detonation of less sensitive high explosives. High explosives are often mixed with inert materials to reduce sensitivity and lower brisance, as in the case of dynamite.