What happens when an explosive is detonated?

By David S. Moore

Los Alamos scientists are seeking a better understanding of how detonation works chemically. This open-air high-explosives detonation was conducted in 2003.

When an explosion goes off, we often think of the damage it does. We seldom think of explosions as constructive, but explosives have always been a critical component of industries such as mining, construction, transportation and even metal bonding.

Despite great advances in explosives since Alfred Nobel invented dynamite, the concept of detonation still baffles scientists. Although linked with the term “explosion,” detonation is quite a different matter. An explosion is defined as a sudden event that results in a loud noise and the fast, typically spectacular burst that breaks apart and sends pieces flying outward. One example of an explosion is a water heater whose pressure-relief vent for some reason plugs up. The pressure then builds in the water heater to the point that it finally bursts with so much force that the water heater rockets from the basement up into your house. Derived from the Latin word detonare, which means to thunder down, a detonation is what scientists call a supersonic burn-front. Picture someone lighting the fuse on a stick of dynamite. The point at which the material is burning is known as the burn-front — it is the location of the burn as it travels through the fuse material. If the velocity of this burn-front moves slower than the speed of sound (subsonic) along the material, the result is simple burning, also known as deflagration. If the velocity is faster than the speed of sound in a material, it is a supersonic burn-front. It builds a powerful shock wave, one whose incredible pressures can propel metal, break rocks and move earth. It is this type of supersonic burn-front that is known as detonation.

A detonation typically takes place in less than a millionth of a second. Moreover, the density of the materials during detonation is incredibly high and temperatures reach a few thousand degrees. Such a hostile and fast environment makes it extremely difficult to study detonation with the naked eye.

The mystery of detonation centers on the chemical reactions that take place right after the supersonic shock wave hits the material, a process that lasts only a billionth of a second. To unravel this mystery, scientists at Los Alamos National Laboratory combine computer simulations and innovative experiments that verify what the…