Thermal Radiation Damage

Structures

Thermal radiation damage is a direct result of the fireball. The thermal radiation that the fireball creates strikes on exposed surfaces and is absorbed into the material. The intensity that a material receives is up to 1000Watts/cm^2; direct sunlight is 0.14Watts/cm^2 for comparison. Interestingly, the heat that is absorbed by the material is absorbed mostly by the first millimeter. This is because the absorption rate is far slower than the transfer of heat to the rest of the material. Material surfaces can easily reach 1000 degrees C and the longer the exposure, the more penetrating the heat becomes [1].

From the extreme heat exposure that materials experience, combustion of most substances occurs and thousands of fires begin. Some materials, such as dry leaves, grass, paper, fabrics, and like materials, simply incinerate within a certain radius of ground zero.  Here is where some the worst effects of a nuclear detonation come into play, the ensuing firestorm.

The ensuing firestorm is a culmination of a number of things.  These influences include, the intense thermal heat, the blast wave, and feeding or air by the mushroom cloud.  The blast wave contributes two major components that allows the thermal heat to escalate the situation, 1) it causes structures to collapse, exposing flammable materials and rupturing gas lines, and 2) creates high winds.  The high winds combined with the super hot thermal heat, causes super heated hurricane-force winds that generates massive fires for hundreds of square miles.  The severity of this only escalates as the mushroom clouds acts like a air pump, pumping the hot air up vertically and sucking in cooler outside air to replace it, therefore feeding an ever growing fire.  The firestorm has a number of effects of structures.  The ensuing fire burns so hot that asphalt on the streets melts and burns.  With that in mind, it is easy to see what can happen to structures as they melt [3], [4].
 

Human Injury

Damage as a result of thermal radiation is much more severe towards humans. The very intense heating from the fireball causes "flash burns," where the more thermal radiation absorbed, the worse the burn becomes.  Interestingly, anyone within 10 miles of the blast will become blind whether their eyes are open, or shut [3]Below is a chart showing the effects of burns on humans [1].
 
 
Severity Effects
Unit of Heat / Range
1st Degree burns Not serious, no tissue destruction. Painful and reddening of skin. Continues for minutes to hour.  3.2cal/cm^2 18km
2nd Degree burns Damage to dermal tissue, some killed. Pain and reddening with blisters. Regenerating ability, no scars. Possible infection. 6 cal/cm^2 14.4km
3rd Degree burns Tissue death throughout skin. No regeneration w/o grafting. Scarring, serious risk of infection, and serious fluid loss. 10 cal/cm^2 12km
4th & 5th Degree Destroys tissue below skin: muscle, connective tissue. Can cause exposed flesh to flash into steam, flaying exposed body area to the bone. 100 cal/cm^2 5km

Below are equations that expand on the destructive radius equations given before by having the constant value known for each type of burn [1].

Where the radius is in km, and Y is the yield of the bomb in kT.

Continuing on the firestorm, the humans effects are gruesome.  Two major effects are seen.  The first is that the high winds cause large amounts of poisonous gas that people inhale and die from.  The second is the burning of people due to the heat.  The air itself is so hot during a firestorm that a person who is on fire can jump into water, stop the burning, but then only arise out of the water to immediately catch fire as soon as they come into contact with the air [3].