Which phase of a blast involves air rushing back to fill a vacuum?

The phase of a blast that involves air rushing back to fill a vacuum is known as the negative phase. After the initial explosion creates a high-pressure wave that expands outward—referred to as the positive phase—there is a rapid decrease in pressure that follows. This decrease creates a vacuum that must be filled, causing surrounding air to rush back in towards the center of the explosion. This rushing air is characteristic of the negative phase and plays a crucial role in the overall dynamics of the blast wave.

Understanding this phase is important for fields such as explosive ordnance disposal and construction safety, where recognizing the impact of shock waves can influence operational decisions. The other phases mentioned relate to different aspects of a blast's effects: the positive phase is the initial outward wave, the explosion phase describes the overall event, and the fragmentation phase deals with the dispersal of debris, but it is the negative phase that specifically focuses on the vacuum effect.