Effects of a Nuclear Explosion

Damage caused by nuclear explosions can vary greatly, depending on the weapon's yield (measured in kilotons or megatons), the type of nuclear fuel used, the design of the device, whether it's exploded in the air or at earth's surface, the geography surrounding the target, whether it's winter or summer, hazy or clear, night or day, windy or calm. Whatever the factors, though, the explosion will release several distinct forms of energy. One form is the explosive blast. Other forms are direct nuclear radiation and thermal radiation. And then there's radioactive fallout -- not exactly energy released by the explosion, but still a destructive result.

Explosive Blast
Much of the damage inflicted by a nuclear explosion is the result of its shock wave. There are two components to a blast's shock wave. First, there's the wall of pressure that expands outward from the explosion. It is this pressure, measured in psi (pounds per square inch), that blows away the walls from buildings. A typical two-story house subjected to 5 psi would feel the force of 180 tons on the side facing the blast. (Download the Quicktime movie entitled house to see an example of a building subjected to this type of pressure.) Additionally, the blast creates a 160 mile-an-hour wind. And that's only at 5 psi. The wind speed following a 20 psi blast would be 500 mph!

Direct Nuclear Radiation
A nuclear detonation creates several forms of nuclear, or ionizing, radiation. The nuclear fission (atom splitting) and nuclear fusion (atom combining) that occur to produce the explosion release, either directly or indirectly, neutrons, gamma rays, beta particles, and alpha particles. Neutrons are heavy particles that are released from atoms' nuclei. These tiny "missiles" can easily penetrate solid objects. Another penetrating form of radiation is gamma rays, which are energetic photons. Both of these types of radiation can be deadly. Beta and alpha particles are less dangerous, having ranges of several meters and several centimeters, respectively. Alpha particles can cause harm only if they are ingested.

Thermal Radiation
You don't have to be close to ground zero to view the bright flash created by the exploding bomb. The flash from a bomb has been viewed from hundreds of miles away. In addition to being intensely bright, this radiation is intensely hot (hence the name "thermal"). If you're seven miles away from a one megaton explosion, the heat emanating from the fireball will cause a first-degree burn (equivalent to a bad sunburn ) to any exposed skin facing the light. If you're six miles away, it will cause second-degree burns. And if you're five miles away, the thermal radiation will cause third-degree burns -- a much more serious injury that would require prompt medical attention.

The intense heat would also ignite a "mass fire" -- i.e., a fire that could cause large areas to simultaneously burst into flames.

Fallout
You've seen the image: a mushroom cloud created by a nuclear explosion. Produced with a detonation at or near the earth's surface, this type of explosion results in far-ranging radioactive fallout. Earth and debris -- made radioactive by the nuclear explosion -- rises up, forming the mushroom cloud's stem. Much of this material falls directly back down close to ground zero within several minutes after the explosion, but some travels high into the atmosphere. This material will be dispersed over the earth during the following hours, days, months. In fact, some of the particles rising up through the mushroom will enter the stratosphere, where they could remain for tens of years.

Obviously, if a thermonuclear bomb exploded close to your home, you'd have little hope of surviving the blast. But what if one exploded 5 miles away, or 20 miles away? And what about radioactive fallout?

Learn about a nuclear weapon's "zones of destruction" -- choose between a relatively small detonation at earth's surface, which will produce substantial fallout, and an especially destructive large detonation at high altitude.

1 Megaton Surface Blast: Pressure Damage

The fission bomb detonated over Hiroshima had an explosive blast equivalent to 12,500 tons of TNT. A 1 megaton hydrogen bomb, hypothetically detonated on the earth's surface, has about 80 times the blast power of that 1945 explosion.

Radius of destructive circle: 1.7 miles
12 pounds per square inch

At the center lies a crater 200 feet deep and 1000 feet in diameter. The rim of this crater is 1,000 feet wide and is composed of highly radioactive soil and debris. Nothing recognizable remains within about 3,200 feet (0.6 miles) from the center, except, perhaps, the remains of some buildings' foundations. At 1.7 miles, only some of the strongest buildings -- those made of reinforced, poured concrete -- are still standing. Ninety-eight percent of the population in this area are dead.

Radius: 2.7 miles
5 psi

Virtually everything is destroyed between the 12 and 5 psi rings. The walls of typical multi-story buildings, including apartment buildings, have been completely blown out. The bare, structural skeletons of more and more buildings rise above the debris as you approach the 5 psi ring. Single-family residences within this this area have been completely blown away -- only their foundations remain. Fifty percent of the population between the 12 and 5 psi rings are dead. Forty percent are injured.

Radius: 4.7 miles
2 psi

Any single-family residences that have not been completely destroyed are heavily damaged. The windows of office buildings have been blown away, as have some of their walls. The contents of these buildings' upper floors, including the people who were working there, are scattered on the street. A substantial amount of debris clutters the entire area. Five percent of the population between the 5 and 2 psi rings are dead. Forty-five percent are injured.

Radius: 7.4 miles
1 psi

Residences are moderately damaged. Commercial buildings have sustained minimal damage. Twenty-five percent of the population between the 2 and 1 psi rings have been injured, mainly by flying glass and debris. Many others have been injured from thermal radiation -- the heat generated by the blast. The remaining seventy-five percent are unhurt.

1 Megaton Surface Blast: Fallout

One of the effects of nuclear weapons detonated on or near the earth's surface is the resulting radioactive fallout. Immediately after the detonation, a great deal of earth and debris, made radioactive by the blast, is carried high into the atmosphere, forming a mushroom cloud. The material drifts downwind and gradually falls back to earth, contaminating thousands of square miles. This page describes the fallout pattern over a seven-day period.

Assumptions
Wind speed: 15 mph
Wind direction: due east
Time frame: 7 days

3,000 Rem*
Distance: 30 miles
Much more than a lethal dose of radiation. Death can occur within hours of exposure. About 10 years will need to pass before levels of radioactivity in this area drop low enough to be considered safe, by U.S. peacetime standards.

900 Rem
Distance: 90 miles
A lethal dose of radiation. Death occurs from two to fourteen days.

300 Rem
Distance: 160 miles
Causes extensive internal damage, including harm to nerve cells and the cells that line the digestive tract, and results in a loss of white blood cells. Temporary hair loss is another result.

90 Rem
Distance: 250 miles
Causes a temporary decrease in white blood cells, although there are no immediate harmful effects. Two to three years will need to pass before radioactivity levels in this area drop low enough to be considered safe, by U.S. peacetime standards.

*Rem: Stands for "roentgen equivalent man." This is a measurement used to quantify the amount of radiation that will produce certain biological effects.

25 Megaton Air Blast: Pressure Damage

Radius of destructive circle: 6.5 miles
12 pounds per square inch

The remains of some buildings' foundations are visible. Some of the strongest buildings -- those made of reinforced, poured concrete -- are still standing. Ninety-eight percent of the population within this area are dead.

Radius: 10.7 miles
5 psi

Virtually everything is destroyed between the 12 and 5 psi rings. The walls of typical multi-story buildings, including apartment buildings, are completely blown out. As you move from the center toward the 5 psi ring there are more structural skeletons of buildings standing. Single-family residences within this this area have been completely blown away -- only their foundations remain. Fifty percent of the population between the 12 and 5 psi rings are dead. Forty percent are injured.

Radius: 20 miles
2 psi

Any single-family residences that are not completely destroyed are heavily damaged. The windows of office buildings have been blown away, as have some of their walls. The contents of these buildings' upper floors, including the people who were working there, are scattered on the street. A substantial amount of debris clutters the entire area. Five percent of the population between the 5 and 2 psi rings are dead. Forty-five percent are injured.

Radius: 30.4 miles
1 psi

Residences are moderately damaged. Commercial buildings have sustained minimal damage. Twenty-five percent of the population between the 2 and 1 psi rings are injured, mainly by flying glass and debris. Many others have been injured from thermal radiation -- the heat generated by the blast. The remaining seventy-five percent are unhurt.

NOTE: This information has been drawn mainly from "The Effects of Nuclear War" (Washington: Office of Technology Assessment, Congress of the United States, 1979) and the PBS Special "Race For The Superbomb"

The zones of destruction described on this page are broad generalizations and do not take into account factors such as weather and geography of the target.