If it has not been adequately purified during manufacture it can degrade over time to even more unstable forms. This makes nitroglycerin highly dangerous to transport or use. In its undiluted form, it is one of the worlds most powerful explosives, comparable to the more recently developed RDX and PETN. Early in its history,  liquid nitroglycerin was found to be  "desensitized" by freezing it at a temperature below 45 to 55 °F (7 to 13 °C) depending on its purity. Its sensitivity to shock while frozen is somewhat unpredictable: "It is more insensitive to the shock from a fulminate cap or a rifle ball when in that condition but on the other hand it appears to be more liable to explode on breaking, crushing, tamping, etc." Frozen nitroglycerine is much less energetic than liquid, and so must be thawed before use. Thawing it out can be extremely sensitizing, especially if impurities are present or the warming is too rapid. Ethylene glycol dinitrate or another polynitrate may be added to lower the melting point and thereby avoid the necessity of thawing frozen explosive.Chemically "desensitizing" nitroglycerin is possible to a point where it can be considered about as "safe" as modern high explosives, such as by the addition of ethanol, acetone, or dinitrotoluene. The nitroglycerin may have to be extracted from the desensitizer chemical to restore its effectiveness before use, for example by adding water to draw off ethanol used as a desensitizer. Detonation
Nitroglycerin and any diluents can deflagrate (burn).
The explosive power of nitroglycerin derives from detonation: energy from the initial decomposition causes a strong pressure wave that detonates the surrounding fuel. This is a self-sustained shock wave that propagates through the explosive medium at 30 times the speed of sound as a near-instantaneous pressure-induced decomposition of the fuel into a white-hot gas. Detonation of nitroglycerin generates gases that would occupy more than 1,200 times the original volume at ordinary room temperature and pressure. The heat liberated raises the temperature to about 5,000 °C (9,000 °F). This is entirely different from deflagration, which depends solely upon available fuel regardless of pressure or shock. The decomposition results in a much higher ratio of energy to gas moles released compared to other explosives, making it one of the hottest detonating high explosives. Manufacturing
Nitroglycerin can be produced by acid-catalyzed nitration of glycerol (glycerin). The industrial manufacturing process often reacts glycerol with a nearly 1:1 mixture of concentrated sulfuric acid and concentrated nitric acid. This can be produced by mixing white fuming nitric acid—a quite expensive pure nitric acid in which the oxides of nitrogen have been removed, as opposed to red fuming nitric acid, which contains nitrogen oxides—and concentrated sulfuric acid. More often, this mixture is attained by the cheaper method of mixing fuming sulfuric acid, also known as oleum—sulfuric acid containing excess sulfur trioxide—and azeotropic nitric acid (consisting of about 70% nitric acid, with the rest being water). The sulfuric acid produces protonated nitric acid species, which are attacked by glycerols nucleophilic oxygen atoms.