The Effects of Nuclear War
Chapter 2
GENERAL DESCRIPTION OF EFFECTS
Thermal Radiation
Approximately 35 percent of the energy from a nuclear explosion is an intense burst of thermal radiation, i.e., heat. The effects are roughly analogous to the effect of a 2-second flash from an enormous sunlamp. Since the thermal radiation travels at the speed of light (actually a bit slower, since it is deflected by particles in the atmosphere), the flash of light and heat precedes the blast wave by several seconds, just as lightning is seen before the thunder is heard.
The visible light will produce “flashblindness” in people who are looking in the direction of the explosion. Flashblindness can last for several minutes, after which recovery is total. A 1-Mt explosion could cause flashblindness at distances as great as 13 miles [21 km] on a clear day, or 53 miles [85 km] on a clear night. If the flash is focused through the lens of the eye, a permanent retinal burn will result. At Hiroshima and Nagasaki, there were many cases of flashblindness, but only one case of retinal burn, among the survivors. On the other hand, anyone flashblinded while driving a car could easily cause permanent injury to himself and to others.
Skin burns result from higher intensities of light, and therefore take place closer to the point of explosion. A 1-Mt explosion can cause first-degree burns (equivalent to a bad sunburn) at distances of about 7 miles [11 km], second-degree burns (producing blisters that lead to infection if untreated, and permanent scars) at distances of about 6 miles [10 km], and third-degree burns (which destroy skin tissue) at distances of up to 5 miles [8 km]. Third-degree burns over 24 percent of the body, or second-degree burns over 30 percent of the body, will result in serious shock, and will probably prove fatal unless prompt, specialized medical care is available. The entire United States has facilities to treat 1,000 or 2,000 severe burn cases; a single nuclear weapon could produce more than 10,000.
The distance at which burns are dangerous depends heavily on weather conditions. Extensive moisture or a high concentration of particles in the air (smog) absorbs thermal radiation. Thermal radiation behaves like sunlight, so objects create shadows behind which the thermal radiation is indirect (reflected) and less intense. Some conditions, such as ice on the ground or low white clouds over clean air, can increase the range of dangerous thermal radiation.