has passed. More recently, laboratory scale shock tubes driven by fuel-air mixtures have been developed that produce realistic blast waves and can be operated in more ordinary laboratory facilities. Because the molar volume of gas is much less, the jet effect is a fraction of that for compressed-gas driven shock tubes. To date, the smaller size and lower peak pressures generated by these shock tubes make them most useful for preliminary, nondestructive testing of materials, validation of measurement equipment such as high speed pressure transducers, and for biomedical research as well as military applications. Operation A simple shock tube is a tube, rectangular or circular in cross-section, usually constructed of metal, in which a gas at low pressure and a gas at high pressure are separated using some form of diaphragm. See, for instance, texts by Soloukhin, Gaydon and Hurle, and Bradley. The diaphragm suddenly bursts open under predetermined conditions to produce a wave propagating through the low pressure section. The shock that eventually forms increases the temperature and pressure of the test gas and induces a flow in the direction of the shock wave. Observations can be made in the flow behind the incident front or take advantage of the longer testing times and vastly enhanced pressures and temperatures behind the reflected wave. The low-pressure gas, referred to as the driven gas, is subjected to the shock wave. The high pressure gas is known as the driver gas. The corresponding sections of the tube are likewise called the driver and driven sections. The driver gas is usually chosen to have a low molecular weight, (e.g., helium or hydrogen) for safety reasons, with high speed of sound, but may be slightly diluted to 'tailor' interface conditions across the shock. To obtain the strongest shocks the pressure of the driven gas is well below atmospheric pressure (a partial vacuum is induced in the driven section before detonation). The test begins with the bursting of the diaphragm. Several methods are commonly used to burst the diaphragm. A mechanically-driven plunger is sometimes used to pierce it or an explosive charge may be used to burst it. Another method is to use diaphragms of plastic or metals to define specific bursting pressures. Plastics are used for the lowest burst pressures, aluminum and copper for somewhat higher levels and mild steel and stainless steel for the highest burst pressures. These diaphragms are frequently scored in