With the increasing popularity of combustion driving in strong shock tube experiments, the possibility of detonation must be considered seriously. In addition to the extreme and relatively well-known conditions associated with a detonation, there exists a phase during the transition from a flame to a detonation during which pressures and velocities of propagation can exist which are higher than those associated with the fully formed detonation. This has been discussed theoretically by Oppenheim (1952) and has been shown experimentally by several workers. A luminous front having a higher than detonation velocity has been observed by Bone, Fraser & Wheeler (1936) and others. J. B. Smith (1949), using calibrated burst diaphragms at the end of a pipe, has observed reflected pressures in fuel gas-air, acetylene-air, and hydrogen-air mixtures which were approximately four times greater than those associated with a reflected normal detonation. Turin & Huebler (1951), using quartz pressure transducers in the side of a tube, observed pressures during this transition process about three and a half times higher than those at a later time when detonation was fully developed. They worked with Toledo natural gas. Mooradian & Gordon (1951) also have clear indications of this phenomenon with hydrogen-air mixtures.