How a shock becomes an explosion
Nitroglycerin stores chemical energy in a compact liquid. A sufficiently strong disturbance can start its molecules decomposing—a rapid chemical change that releases heat and produces hot gases. The heat speeds further decomposition, while the gases expand sharply. In a confined or rapidly changing volume, that expansion creates the destructive pressure of an explosion.
The danger is not that every vibration automatically sets it off. Rather, nitroglycerin is unusually sensitive to impacts and other disturbances compared with many explosives. A shock can create a tiny region of intense compression and heating, allowing the reaction to begin there and then race through the surrounding material. The initial disturbance may be local; the energy released by the reaction is not.
Why handling it was a problem
A liquid is also difficult to keep safely in place: it can slosh, leak, or be exposed to knocks during transport. In the 19th century, Alfred Nobel helped address this problem by absorbing nitroglycerin into a porous material to make dynamite. The material made the explosive easier to handle and use, though it did not make it harmless.
That distinction explains nitroglycerin’s reputation. Its danger comes from how readily a small initiating event can unleash energy stored throughout the material. A jolt need not supply the force of the eventual blast; it only has to start the reaction.
