APPENDIX D (Continued)
Lung damage, a serious injury usually requiring hospitalization, and eardrum rupture,
a minor injury often requiring no treatment at all, are two trauma points that are useful. The
threshold level of incident pressure that is estimated to cause lung damage is about 10 psi
(0.7 kgf/sq cm). The threshold value for eardrum rupture is around 3.2 psi (0.22 kgf/sq cm) and
that overpressure associated with a 50-percent probability of eardrum rupture ranges from 13 to
19 psi (0.91 to 1.33 kgf/sq cm). Casualties requiring medical treatment from direct blast effects
could theoretically be produced by overpressures greater than 10 psi (0.7 kgf/sq cm). However,
direct blast injuries will not occur by themselves; and in general, other effects, such as indirect
blast injuries, are so severe at the ranges associated with these overpressures that victims with
direct blast injuries will comprise a very small part of the total.
Injury From Drag Forces and Debris. Drag forces of the blast can be extremely
severe. Considerable injury can result at greater distances from being hit by debris or being
blown over. The distance at which the peak overpressure is about 3 psi (0.21 kgf/sq cm) is a
reasonable reference distance at which the probability of serious indirect injury is high. Injuries
can occur at greater ranges, and casualties will be generated at greater ranges, but not
The probability of injury from debris depends on a number of factors: the number of
projectiles available, the terrain, and the size and weight of the debris that will be low velocity in
nature. None will be high velocity, such as is produced by direct bomb fragments.
The weight of an object and the duration of the drag force winds determine how fast it
will go. Light objects will be accelerated rapidly up to the maximum possible velocity, whereas
heavy objects may not be. The velocity is important, because the probability of a penetrating
injury increases with increasing velocity, particularly for small, sharp missiles, such as glass
Heavy blunt missiles will not penetrate, but can result in significant injury,
particularly fractures. For example, a velocity of about 15 feet per second is a threshold velocity
for skull fracture for a 10-pound object.
The drag forces of the blast winds are strong enough to displace even large objects, such
as vehicles. These can result in very serious crush injuries. Humans themselves can become a
missile and be displaced significant distances. The resulting injuries sustained are termed
translational injuries. The probability and the severity of injury depend on the velocity of the
human body at the time of impact.