Blast Effects on Humans
Blast damage is caused by the arrival of the shock wave created by the nuclear explosion. Humans are actually quite resistant to the direct effect of overpressure. Pressures of over 40 psi are required before lethal effects are noted.
The danger from overpressure comes from the collapse of buildings that are generally not as resistant. Urban areas contain many objects that can become airborne, and the destruction of buildings generates many more. The collapse of the structure above can crush or suffocate those caught inside. Serious injury or death can also occur from impact after being thrown through the air.
The blast also magnifies thermal radiation burn injuries by tearing away severely burned skin. This creates raw open wounds that readily become infected.