Which phases are identified in the blast effects of an explosion?

In the context of explosions, the blast effects are typically identified by their pressure phases, specifically the positive pressure phase and the negative pressure phase. The positive phase occurs when the explosion generates an initial shockwave that compresses the air and causes a rapid increase in pressure. This is followed by the negative phase, which occurs as the shockwave moves away, leading to a drop in pressure as the surrounding air rushes back to fill the void created by the explosion.

Understanding these phases is crucial for assessing the extent of damage and for forming effective responses to such incidents. The positive phase is responsible for the immediate impact that can cause injury or damage, while the negative phase can contribute to further destructive effects. This distinction is vital for training and preparation in handling scenarios involving explosions. The other options offered do not accurately classify the effects of an explosion in terms of pressure phases, thus making this identification essential for appropriate responses in emergency situations.