Numerous experiments on the nature and effects of
blast have been made in the United States and Great
Britain, and hundreds of thousands of soldiers and
civilians have personally experienced the effects of blast
by bombs, shells, and mines. The subject of blast is
treated in this section mainly for the benefit of soldiers
who have not experienced these effects. The facts and
observations set forth below are based largely on experiments
conducted in England, the results of which
appeared in The Bulldozer, a British military publication.
Before the war, the No. 1 bogey of the civilian population
was poison gas and the No. 2 bogey was blast. During
the earlier stages of the Japanese war against
the Chinese, and also during the Spanish Civil War,
stories were circulated on the streets to the effect that
persons in the war-torn areas were being found dead
in streets and houses, without any visible wounds. We
now know that these stories were largely untrue, and
that blast--as far as human lives are concerned--is
by no means the terror that some persons have imagined.
Nevertheless, we know that blast is destructive
to buildings and equipment, according to the circumstances,
and that its effects--rather than the actual
blast--are injurious or fatal to persons under certain conditions.
2. WHAT IS BLAST?
Generally speaking, blast is a violent disturbance of
the air, and is produced by any very sudden movement.
One characteristic of a blast wave is its sudden start.
The air pressure reaches its peak immediately and then
falls below normal. The pressure is below normal
longer than it is above normal. These periods are
known as the pressure and suction phases of blast. The
pressure wave travels outward at a speed a little faster
than that of ordinary sound, which is approximately
1,000 feet per second.
When a bomb bursts, the case swells like a balloon
to half again or more of its original size; then it cracks
into fragments, and the compressed gases from the explosion
come out fast--up to 10,000 feet per second
or faster. The surrounding air does not have time to
get out of the way, and something like a solid wall of
high pressure is formed. The gases, some few feet
outward from the bomb, cool off and lose speed, but
the push they give to the air still carries on as the
pressure wave. (Such waves can actually be photographed.) As
the wave moves on, its pressure spreads wider and
wider and gradually decreases until it becomes
an ordinary sound wave.
3. WHAT ARE THE EFFECTS OF BLAST?
As we hear it, a nearby explosion makes a cracking
sound while a distant one makes a booming sound.
When a blast wave hits an object, there are two different
effects: one caused by the pressure of the wave
and the other caused by the immediate forward movement
of the air behind the pressure wave. Therefore,
an object in the path of a blast is compressed and
pushed away from the explosion and then drawn
toward it--by suction.
In the case of large objects near the explosion, the
pressure phase is the most damaging. For example, the
walls of ordinary houses are pushed in by the pressure.
(It takes about 50 pounds per square inch to push in
a wall and about 10 pounds to push in a window.)
Large objects some distance from the explosion suffer
most from the suction phase. For example, pressure
from the explosion of a large bomb would not be great
enough to push in the walls of a house, but the suction
immediately following the pressure wave would suddenly
take away most of the normal atmospheric
pressure in front of the structure. Because of this
partial vacuum outside of the house, its walls would be
pushed outward by the normal pressure from inside.
Although the walls would be pushed out in all directions, the
main force of inside pressure would be
against the wall facing toward the explosion.
In the case of small objects, movement is more important
than pressure. Leaves and branches are torn
off trees. Clothes may be ripped off, and people flung
about. Actually, far more casualties are caused by
this flinging about by blast than by the direct blast
effect. Therefore, it is always best to lie down when
exposed to blast bombs, not to mention the protection
afforded against fragments.
In an area affected by blast, the amount of protection
available depends largely on the number and size
of obstacles behind which personnel can seek refuge.
The blast wave can be thought of as having a
high-frequency, short-wave pressure component and a
low-frequency, long-wave suction component. The pressure
component, like light but unlike sound, cannot get
around a medium-size obstacle. The suction component,
like ordinary sound, will get around most obstacles
smaller than a medium-size hill.
The result is that behind an obstacle the blast wave
is quite a different shape. The high-pressure part is
practically obliterated; the suction part remains.
Fortunately, it is the pressure part that is dangerous
to human beings, either because it knocks them about
or because it damages their ears and lungs; therefore,
a man behind a wall or rock is unlikely to be hurt,
even though he is quite close to a bomb--that is, as
long as the wall itself does not come down on top of
Several months ago two sailors were together when
a bomb hit nearby. One just managed to get around
the corner of a wall and was unhurt, while the other
did not make it and was never seen again.
In the same way, blast does not easily get into closed
spaces from the outside. Even comparatively fragile
underground shelters can furnish complete protection
against blast from air-burst bombs. Once a whole
shelter full of people were uninjured by a bomb falling
10 feet away.
But the results are very different when an explosion
occurs inside confined space, where reflections of blast
waves come from the walls and where the internal
pressure is much increased.
What is worse, blast waves from an inside explosion
will run along tunnels for great distances without
losing any of their strength, and they will even travel
No tunnel shelter is safe from bombs exploding just
inside, unless it is provided with baffle walls, sharp
turns, or blast traps. Fortunately, this lesson has been
well learned by now in military establishments.
We now know, largely from experiments, what blast
does to animals and men. It is really much less hazardous
than people used to think.
To summarize previous statements, all the damage
to buildings at close range is due to the pressure and
not to the suction component.
There is no time for the suction to draw the air
out of a lung, as some rumors have suggested.
The pressure phase affects chiefly those parts of the
body that have air hollows behind them. The most important
ones are the ears and the lungs. The effect
on the ear is simply to burst the delicate membrane
of the ear drum. This occurs at comparatively low
pressure--although this pressure is a great deal higher
than that accepted as safe for gunners. Fortunately,
burst ear drums usually cause only temporary casualties.
The ear drum re-forms and hearing is not permanently
The lung is a more serious concern, but only when
the victim is very near the explosion. A man can barely
survive a pressure of between 400 and 500 pounds per
square inch--the kind of thing that would completely
destroy any ordinary building.
Two instances illustrate this:
a. Three men in a small brick shed, in the middle
of which a 50-kilogram bomb burst, are alive and well
today, although the building itself was scattered over
many square yards.
b. A man, 25 feet from a bomb in the open but fortunately
lying down, not only remained fully conscious
but was able to get up immediately after the explosion
and assist other victims.
The effect of blast on the lungs is to push in the ribs
and press them against the lungs, bruising them or
rupturing the small blood vessels and lung spaces and
thereby leading to more or less extensive internal
bleeding. The immediate effect may not be noticed, but
it is similar to a severe case of pneumonia, since the
amount of lung space available for breathing is reduced.
The treatment is simply rest; obviously a man taking
violent exercise immediately after exposure to blast
is likely to injure himself fatally.
It is surprising how very few cases of true blast
deaths have occurred in all the bombing of this war--so
few, in fact, that the doctors have great difficulty
in getting good case histories. The reason is, of course,
that you have to be very close to a bomb to get blasted,
and if you are very close, you are far more likely to be
killed by splinters.
Most of the so-called mysterious deaths in dugouts
and shelters were certainly not due to blast, but most
often due to carbon monoxide poisoning resulting from
poor ventilation, and sometimes from explosive gases.
4. WHAT ARE THE EFFECTS OF SHOCK WAVES?
In combined operations, men have to face not only
blast in the air, but shock waves in water.
In principle, these shock waves are the same as blast,
but there are two big differences in scale. The shock
wave from an underwater explosion travels faster and
farther--about 6,000 feet per second instead of 1,000--and
it has a much higher pressure, measured in tons
per square inch instead of pounds. But it is, accordingly,
of much shorter duration.
Fortunately, the effect of the shock wave in water
is greatest on deeply submerged objects and least on
those on the surface. This is because the free surface
can yield to the wave, so on the actual surface itself
the effect is practically nil unless the intensity is such
that the surface is actually flung up into the air--as
in the spray dome above a mine.
Experiments and trials have shown that for a man
in the water, the safest position is floating on his back
and that the next safest is swimming. Treading water
or hanging vertically to some floating object exposes
the lungs and abdomen to a more severe shock.
5. WHAT ABOUT CONCUSSION?
There is one other condition which is sometimes confused
with blast--concussion. This usually refers to
supposed effects on personnel in gunrooms and magazines
due to large bombs or shells exploding in the
ground nearby. Experiments have shown that this is
not a serious danger.
Real concussion can be caused only by a hit on the
head--and such a blow must be caused by a really hard
object. Certainly no one in a room can be exposed to
concussion except from some flying object. Nevertheless,
the effect of shock is an alarming and distressing
experience; but if the explosion is not so close that it
actually breaks into the room and throws its contents
about, no one inside will sustain a concussion.
The research on blast and concussion has done something
to provide protection where protection is necessary. And
perhaps its real value lies even more in
debunking the many misconceptions about mysterious
There are enough real dangers in war to make
worrying about the others a waste of time.