[Ammonium nitrate] is a crystalline powder, varying in color from almost white to brown. In military use it is mixed (as an oxidizer or promoter of combustion) with TNT in the manufacturer of 'Amatol' which is used primarily as a bursting charge in demolition bombs. In peacetime use it is an excellent source of nitrogen for all crops, and it is one of the most concentrated forms of nitrogen fertilizer (35%N). Ammonium nitrate usually cannot be detonated by heat or friction, it is comparatively insensitive. However, it may be exploded under favorable conditions by severe mechanical shock or by sufficiently heavy initiation of an intermediate explosive agent (such as detonation with a fulminating cap used in exploding dynamite). Fertilizer piles containing this material should not be blasted. A shock may mechanically set up a chain of events which will result in the detonation of the entire mass of material. Shock waves propagated at a velocity of about 5,000 meters per second, or over, appear to be required. Incidents have been reported in laboratories when the material was heated rapidly, but larger quantities in wooden kegs and casks have been exposed to test fires without detonation. However, impure salts may be exploded by relatively high initiation. If ammonium nitrate is mixed with carbonaceous materials. it is exploded more readily. It is sensitized by the presence of explosive substances like nitrocellulose or aromatic nitro compounds, or of non-explosive combustible substances like sulphur, charcoal, flour, sugar, or oil and by incombustible substances such as zinc, cadmium, and copper. Ammonium nitrate is not very flammable at atmospheric temperatures, and is considered an incombustible salt. However, when undergoing decomposition it is accompanied by a series of thermal chemical changes involving heat-absorbing (endothermic, - 41,3000 calories) and subsequent heat evolving (exothermic, + 51,000 calories) reaction and when subjected to temperature of 350 F to 390 F rapid decomposition occurs with production of a whole series of toxic oxides-of-nitrogen gasses (N2O, NO2, N2O2, N2O3 and N2O4) evidenced by brown to orange-reddish fumes. The progressive acceleration of successive changes may result in the production of temperatures as high as 2700 F with pressures of 160,000 pounds per square inch. One initial reaction at more moderate temperatures results in the formation of oxygen, nitrogen and steam, promoting self sustained combustion (reducing the effectiveness of the smothering action of steam.)