Chapter 1 – Thermal Radiation (or Heat)

Thermal Radiation (or Heat)

An important effect of a nuclear detonation is the generation of an intense thermal pulse of energy (i.e., the nuclear flash). The thermal effect causes burns to people and may ignite certain flammable materials. The potential for fire ignition in modern cities from the nuclear thermal effect is poorly understood but remains a major concern. Fires may be started by theinitial thermal effect igniting flammable materials. Secondary fires may be started by theignition of gas from broken gas lines and ruptured fuel tanks.
Fires destroy infrastructure, pose a direct threat to survivors and responders, and may threaten  people taking shelter or attempting to evacuate. If fires are able to grow and coalesce, a firestorm10could develop that would be beyond the abilities of firefighters to control. However, experts suggest in the nature of modern US city design and constructionmay make a raging firestorm unlikely.
The SD zone is not expected to be conducive to fires because of the enormous wind that ensues and because flammable sources are buried in deep rubble; however, leaking gas lines may still ignite. The MD zone is more likely to sustain fires because
many buildings are expected to remain standing, but damage to infrastructure, such as blown out windows and broken gas lines and fuel tanks, is still extensive. Depending on the flammability of various materials and distance from ground zero, blast winds can either extinguish or fan the burning materials. The LD zone with minor infrastructure damage may also have fires, but these should be more easily contained and mitigated.
A nuclear detonation is accompanied by a thermal pulse. The thermal pulse intensity at any given point will depend on distance from the detonation, the height of burst, and on any shielding from structures. In general, the thermal hazard is greatest in the case of a low-altitude air burst. General thermal effects will be less for ground bursts resulting from less direct line-of-sight contact with the energy radiating from the detonation. Ground bursts result in a large part of the thermal energy being absorbed by the ground and any buildings around ground zero. Partial and sometimes complete shadowing of the thermal pulse and fireball may be provided to people inside or behind buildings and other structures. Terrain irregularities, moisture, and various aerosols in the air near the surface of the earth will tend to reduce the amount of thermal energy that is transported at distance.