which the ionizing radiation from higher yield devices is of primary concern, is already well inside the hyper-lethal blast and flash burn areas. Delayed nuclear radiation, "fallout" Apart from the intrinsic "prompt effects" of nuclear detonations, that of thermal flash, blast and initial radiation releases, if any part of the fireball of the nuclear detonation contacts the ground, in what is known as a surface burst, another, comparatively slowly increasing, radiation hazard will also begin to form in the immediate area. Putting aside the possibility of the detonation occurring during an already established heavy rain-storm, the formation of this life-threatening "delayed nuclear radiation" manifests only when the altitude, or "height of burst" of the explosion, is such that both the fireball and the buoyant updrafts it creates, sufficiently heats and lifts the soil that was below it into the core of the mushroom cloud. Once there, the very hot radioactive isotope products of the nuclear reactions that produced the explosion, begin to coalesce with the cooler and denser soil. Upon cooling, this mixture begins to locally fall-out or precipitate-out of the mushroom cloud, falling back to the surface of the earth, near to the point of detonation, over the next few minutes and hours. While the duck and cover countermeasure, in its most basic form, offers a small to negligible protection against fallout, the technique assumes that after the effects of the blast and initial radiation subside, with the latter of which being no longer a threat after about "twenty seconds" to 1 minute post detonation, a person who ducks and covers will realize when it is wise to cease ducking and covering (after the blast and initial radiation danger has passed) and to then seek out a more sheltered area, like an established or improvised fallout shelter to protect themselves from the ensuing potential local fallout danger, as depicted in the film. After all, "Duck and Cover" is a first response countermeasure only, in much the same way that "Drop, Cover and Hold On" is during an earthquake, with the advice having served its purpose once the earthquake has passed, and possibly other dangers—like a tsunami or fallout—may be looming, which then require movement to high ground and radiation protection, respectively. However, if such a shelter is unavailable, the person should then be advised to follow the Shelter in Place protocol, or if given, emergency evacuation advice. Evacuation orders