What occurs during the positive phase of a blast?

During the positive phase of a blast, the blast wave propagates outward from the point of explosion. This wave increases in pressure and pushes the surrounding air ahead of it, creating a shock front that moves through the atmosphere. The intense pressure results in the air being compressed and forced away from the source of the explosion, which is why the correct answer highlights how the blast wave moves and pushes air out.

In contrast, the negative phase or the secondary phase of the blast occurs after this initial positive phase, when the pressure drops and air rushes back in to fill the resulting vacuum. Understanding the characteristics of these phases is crucial for analyzing the effects of blasts in various contexts, such as in military applications or demolitions. The other concepts, such as shrapnel ejection and debris settling, pertain to different aspects of the detonation and its aftermath, rather than the specific dynamics during the positive phase itself.