A-4. Biological Effects of Thermal Radiation
The thermal radiation emitted by a nuclear detonation causes burns in two ways—by direct absorption of the thermal energy through exposed surfaces (flash burns); or by the indirect action of fires in the environment (flame burns). Indirect flame burns can easily outnumber all other types of injury.
a. Thermal radiation travels outward from the fireball in a straight line; therefore, the amount of energy available to cause flash burns decreases rapidly with distance. Close to the fireball all objects will be incinerated. The range for 100 percent lethality will vary with yield, height of burst, weather, environment, and immediacy of treatment. The critical factors determining the degree of burn injury are the flux (calories per square centimeter/second [cal/cm2/sec]) and the duration of the thermal pulse. The total amount of thermal radiation needed to cause a flash partial thickness burn on exposed skin will vary with the yield of the weapon and the nature of the pulse ([Table A-7]). Most burn patients will come from the zones where partial thickness burns occur. In areas where radiation, blast, and thermal intensity are highest, burn victims surviving long enough to reach medical care will be rare.
NOTE
The battle dress uniform (BDU), MOPP gear, or any other clothing will provide additional protection against flash burns. The airspace between the clothing significantly impedes heat transfer and may prevent or reduce the severity of burns, depending on the magnitude of the thermal flux.
Table A-7. Factors for Determining the Probability of Partial Thickness Burns
| YIELD OF WEAPON | 1 KT | 10 KT | 100 KT | 1 MT | 10 MT |
|---|---|---|---|---|---|
RANGE (km) FOR PRODUCTION OF PARTIAL THICKNESS BURNS ON EXPOSED SKIN | 0.78 | 2.1 | 4.8 | 9.1 | 14.5 |
DURATION OF THERMAL PULSE IN SECONDS | 0.12 | 0.32 | 0.9 | 2.4 | 6.4 |
Cal/cm2/sec REQUIRED TO PRODUCE PARTIAL THICKNESS BURNS ON EXPOSED SKIN | 4.0 | 4.5 | 5.3 | 6.3 | 7.0 |
b. Indirect (flame) burns result from exposure to fires caused by the thermal effects in the environment, particularly from ignition of clothing. The larger-yield weapons are more likely to cause firestorms over extensive areas. There are too many variables in the environment to predict either incidence or severity of casualties. Expect the burns to be far less uniform (in degree) and not limited to exposed surfaces. For example, the respiratory system may be exposed to the effects of hot gases produced by extensive fires. Respiratory system burns cause high morbidity and high mortality rates.
c. The initial pulse of radiation in the optical and thermal bands can cause injuries in the forms of flash blindness and retinal scarring. The initial brilliant flash of light produced by the nuclear detonation causes flash blindness. This flash swamps the retina, bleaching out the visual pigments and producing temporary blindness. During daylight hours, this temporary effect may last for about 2 minutes. At night, with the pupil dilated for dark adaptation, flash blindness will affect personnel at greater ranges and for greater durations. Partial recovery can be expected in 3 to 10 minutes, though it may require 15 to 35 minutes for full night adaptation recovery. Retinal scarring is the permanent damage from a retinal burn. It will occur only when the fireball is actually in the individual's field of view and should be a relatively uncommon injury. The location of the scar will determine the degree of interference with vision. Because night vision apparatus electronically amplifies an image, it cannot transmit the flash intensity and will not cause eye injury.