62
7 Physical Effects of Radiological Weapons
7.1 Blast
We are, sadly, all too familiar with the effects of blast, be it from an improvised
explosive device, a belt or vest worn by a suicide bomber, a letter or package sent by
mail, or a vehicle filled with explosives. While explosions can form in solid, liquid,
or gas the most common form is a solid.
Explosives consist of a fuel mixed with an oxidizer. When the explosion is initiated
the fuel and oxidizer react, producing gas and releasing energy. One kilogram of TNT,
for example, will produce 825 L of explosion gases and produces 4.184 MJ of energy
when detonated [2]; when this gas is heated by the energy released by the chemical
reaction the volume expands even further. This is the origin of the blast from an
explosion [2–4].
If the chemical reaction passes through the explosive relatively slowly (lower than
the speed of sound) the material is called a low explosive; high explosive materials
are those in which the chemical reaction proceeds through the material at supersonic
speeds. Explosives in which the chemical reaction moves more rapidly and in which
more energy is released per chemical reaction tend to be more powerful; this can be
increased further by the addition of aluminum powder or other enhancing materials.
As the chemical reaction progresses the expanding hot gas creates a pressure wave
that expands into space. The sudden increase in pressure and temperature creates a
shock wave—a large and abrupt change in pressure in a very small distance—that
causes damage as it encounters objects in its path. If those objects are relatively strong
compared to the energy in the shock wave then they will be physically displaced; if
the objects are relatively weak compared to the strength of the shock wave then they
will be torn apart. The strength of the shock wave drops roughly as the inverse cube
of distance from the source of the explosion.
7.2 Damage to Structures
When the shock wave from an explosion impacts a structure, it will impart pressure
across the entire cross-sectional area of the structure. Due to the relatively large
cross-sectional area of even a small structure, this can exert a large amount of force;
a pressure of only 10 kPa (1.45 psi) applied to a wall three meters high and 10 m
in length (30 square meters) will exert a force of 300,000 N—more than 30 tons of
force—imparted over a fraction of a second. This is enough force to shatter glass
and to collapse many ordinary building materials.
As noted above, an explosion of any significant size can place a tremendous lateral
load on a structure. In addition to the damage caused to the walls and windows (to
be discussed below) this load can also weaken structural members and can cause
a building to collapse entirely or partially; it can also permit a building to remain
standing while being unstable and prone to collapse at a later time, during emergency response activities. Those responding to any bombing attack, regardless of the
7 Physical Effects of Radiological Weapons
7.1 Blast
We are, sadly, all too familiar with the effects of blast, be it from an improvised
explosive device, a belt or vest worn by a suicide bomber, a letter or package sent by
mail, or a vehicle filled with explosives. While explosions can form in solid, liquid,
or gas the most common form is a solid.
Explosives consist of a fuel mixed with an oxidizer. When the explosion is initiated
the fuel and oxidizer react, producing gas and releasing energy. One kilogram of TNT,
for example, will produce 825 L of explosion gases and produces 4.184 MJ of energy
when detonated [2]; when this gas is heated by the energy released by the chemical
reaction the volume expands even further. This is the origin of the blast from an
explosion [2–4].
If the chemical reaction passes through the explosive relatively slowly (lower than
the speed of sound) the material is called a low explosive; high explosive materials
are those in which the chemical reaction proceeds through the material at supersonic
speeds. Explosives in which the chemical reaction moves more rapidly and in which
more energy is released per chemical reaction tend to be more powerful; this can be
increased further by the addition of aluminum powder or other enhancing materials.
As the chemical reaction progresses the expanding hot gas creates a pressure wave
that expands into space. The sudden increase in pressure and temperature creates a
shock wave—a large and abrupt change in pressure in a very small distance—that
causes damage as it encounters objects in its path. If those objects are relatively strong
compared to the energy in the shock wave then they will be physically displaced; if
the objects are relatively weak compared to the strength of the shock wave then they
will be torn apart. The strength of the shock wave drops roughly as the inverse cube
of distance from the source of the explosion.
7.2 Damage to Structures
When the shock wave from an explosion impacts a structure, it will impart pressure
across the entire cross-sectional area of the structure. Due to the relatively large
cross-sectional area of even a small structure, this can exert a large amount of force;
a pressure of only 10 kPa (1.45 psi) applied to a wall three meters high and 10 m
in length (30 square meters) will exert a force of 300,000 N—more than 30 tons of
force—imparted over a fraction of a second. This is enough force to shatter glass
and to collapse many ordinary building materials.
As noted above, an explosion of any significant size can place a tremendous lateral
load on a structure. In addition to the damage caused to the walls and windows (to
be discussed below) this load can also weaken structural members and can cause
a building to collapse entirely or partially; it can also permit a building to remain
standing while being unstable and prone to collapse at a later time, during emergency response activities. Those responding to any bombing attack, regardless of the