What causes the most casualties in a nuclear attack?

The initial blast and the heat of detonation are the primary causes of immediate casualties in a nuclear attack. When a nuclear weapon detonates, it releases an immense amount of energy almost instantaneously, resulting in a powerful shock wave that can obliterate buildings, infrastructure, and anything in its vicinity. This initial explosion produces a staggering heat pulse that can set fires and severely burn individuals within a significant radius of the blast.

The effectiveness and destructive capability of the blast are intensified by factors such as the weapon's yield, detonation height, and geographic location. High-yield nuclear weapons can lead to widespread devastation, resulting in a high number of immediate fatalities and injuries. While radiation exposure and panic following such an event contribute to casualties, they generally do not match the immediate lethality of the blast and thermal effects in the initial phase of a nuclear attack.