What does the secondary blast phase in blast injury refer to?

The secondary blast phase refers specifically to injuries caused by projectiles that are propelled into the air as a result of the explosion. During a blast, the force can displace various objects in the surrounding environment—these can be debris, fragments, or other materials that are thrown outward. This phase is crucial to understanding how blast injuries occur because these projectiles can cause significant trauma when they strike individuals nearby.

In contrast, the other types mentioned in the choices pertain to different mechanisms of injury from a blast. Injuries caused by the blast wave are associated with the primary blast phase, which involves the immediate effects of the overpressure wave. Injuries from heat and fire relate to the thermal effects that can occur during the explosion but do not classify under the secondary phase. Lastly, injuries from structural collapse relate to the physical collapse of buildings or structures due to the blast, which is also not classified as secondary injuries. Therefore, the focus on projectiles propelled by the explosion distinctly identifies the secondary blast injuries within the context of blast trauma.