(a) The threshold level of overpressure for an unreinforced unreflected blast wave that can cause lung-damage is about 1.0 atmosphere.
(b) The threshold level for eardrum rupture is around 0.2 atmospheres; the overpressure associated with a 50 percent probability of eardrum rupture is about 1.1 atmospheres.
(3) Casualties requiring medical treatment from direct blast effects are produced by overpressure between 1.0 and 3.5 atmospheres. However, other effects (such as indirect blast injuries and thermal injuries) are so predominate that patients with only direct blast injuries make up a small part of the patient workload.
b. The drag forces (indirect blast) of the blast winds are proportional to the velocities and duration of the winds. The winds are relatively short in duration, but can reach velocities of several hundred km per hour. Injury can result from missiles impacting on the body or from the physical displacement of the body against objects and structures.
(1) The distance from the point of detonation at which severe indirect injury occurs is greater than that for equally serious direct blast injuries. A high probability of serious indirect injury can occur when the peak overpressure is about 0.2 atmospheres. This range will increase with the increased size of the weapon; for a 1 KT weapon, the range is 0.22 km, whereas for a 20 KT weapon, the range is 0.76 km. At greater ranges injuries will occur and casualties will be generated, but not consistently.
(2) The drag forces of the blast winds produced by a nuclear detonation are so great that almost any form of vegetation or structure will be broken up or fragmented into missiles. Thus, multiple, varied missile injuries will be common, increasing their overall severity and significance. [Table A-3] lists ranges at which significant missile injuries can be expected.
Table A-3. Ranges for Probabilities of Serious Injury from Small Missiles
| RANGES (km) | |||
|---|---|---|---|
| YIELD (KT) | 1% PROBABILITY OF SERIOUS INJURY | 50% PROBABILITY OF SERIOUS INJURY | 99% PROBABILITY OF SERIOUS INJURY |
| 1 | 0.28 | 0.22 | 0.17 |
| 10 | 0.73 | 0.57 | 0.44 |
| 20 | 0.98 | 0.76 | 0.58 |
| 50 | 1.4 | 1.1 | 0.84 |
| 100 | 1.9 | 1.5 | 1.1 |
| 200 | 2.5 | 1.9 | 1.5 |
| 500 | 3.6 | 2.7 | 2.1 |
| 1,000 | 4.8 | 3.6 | 2.7 |
| 1 | INCIDENCE OF INJURY BASED ON SKIN AND TISSUE PERFORATION. | ||
| 2 | MISSILES USED WERE 10 GRAM (gm) IN WEIGHT. | ||
(3) The velocity to which missiles are accelerated is the major factor in causing injury. The probability of a penetration injury increases with increasing velocity, particularly for small, sharp missiles such as glass fragments. Small, light objects are accelerated to speeds approaching the maximum (wind) velocity. [Table A-4] shows data for probability of penetration related to size and velocity of glass fragments.