For the pyrotechnic initiator, see Shock tube detonator The shock tube is an instrument used to replicate and direct blast waves at a sensor or a model in order to simulate actual explosions and their effects, usually on a smaller scale. Shock tubes (and related impulse facilities such as shock tunnels, expansion tubes, and expansion tunnels) can also be used to study aerodynamic flow under a wide range of temperatures and pressures that are difficult to obtain in other types of testing facilities. Shock tubes are also used to investigate compressible flow phenomena and gas phase combustion reactions. More recently, shock tubes have been used in biomedical research to study how biological specimens are affected by blast waves. A shock wave inside a shock tube may be generated by a small explosion (blast-driven) or by the buildup of high pressures which cause diaphragm(s) to burst and a shock wave to propagate down the shock tube (compressed-gas driven). History An early study of compression driven shock tubes was published in 1899 by French scientist Paul Vieille, though the apparatus was not called a shock tube until the 1940s. In the 1940s, interest revived and shock tubes were increasingly used to study the flow of fast moving gases over objects, the chemistry and physical dynamics of gas phase combustion reactions. In 1966, Duff and Blackwell described a type of shock tube driven by high explosives. These ranged in diameter from 0.6 to 2 m and in length from 3 m to 15 m. The tubes themselves were constructed of low-cost materials and produced shock waves with peak dynamic pressures of 7 MPa to 200 MPa and durations of a few hundred microseconds to several milliseconds. Both compression-driven and blast-driven shock tubes are currently used for scientific as well as military applications. Compressed-gas driven shock tubes are more easily obtained and maintained in laboratory conditions; however, the shape of the pressure wave is different from a blast wave in some important respects and may not be suitable for some applications. Blast-driven shock tubes generate pressure waves that are more realistic to free-field blast waves. However, they require facilities and expert personnel for handling high explosives. Also, in addition to the initial pressure wave, a jet effect caused by the expansion of compressed gases (compression-driven) or production of rapidly expanding gases (blast-driven) follows and may transfer momentum to a sample after the blast wave