Studies of blast waves in the past have focused predominantly on the incident shock strength and the following expansion decay during the positive phase. The current experimental and numerical study extends this to include the negative phase with the associated second shock. It is shown that adjustment of the area of the driver section of a shock tube at the diaphragm station will result in the development of the second shock. A range of different driver profiles are examined. Good agreement of the positive phase pressure profile with the Friedlander profile is obtained over a shock Mach number range of 1.11–1.44. Variations in velocity and temperature in both the positive and negative phases are established. It is particularly noted that the propagating second shock is embedded in a flow moving in the opposite direction. A ninety degree corner is positioned at the end of the shock tube to enable high-speed schlieren examination of the diffraction. The distortion of the reflected sound wave from the corner is shown to be different to shock wave diffraction due to the continuously changing velocity and sound speed in the blast expansion wave. As this expansion diffracts at the corner a reflected compression wave develops due to the sudden increase in area. At the same time the trajectory of the shear layer continually changes.