Bomb Shelters, Part II
Give careful consideration to the following as you design your new bomb shelter:

Major cities and military installations are likely targets for a nuclear attack. The closer you are to ground zero, the stronger your bomb shelter needs to be. If you are near a potential target, your bomb shelter should be built underground and reinforced to protect you from the blast effect, the thermal radiation, and the nuclear radiation of a nuclear explosion. If you are far from a potential target, you may still need a bomb shelter to protect you from the radioactive fallout following a nuclear explosion. For a list of targets in your state, click here.

Half of the energy from a nuclear explosion is expended in the blast effect - a tremendous increase in air pressure radiating outward from the point of detonation in all directions. The blast of a one-megaton nuclear device detonating at surface level would destroy everything within a half mile, including underground bomb shelters. At three quarters of a mile, strong underground bomb shelters may withstand such a blast. Structures at the surface would be subjected to the following overpressure:

Distance from epicenter - pounds per square inch - wind velocity - effects

1.7 miles - 12 psi - 300+ mph - everything blown to pieces
2.7 miles - 5 psi - 165 mph - only the steel skeletons of buildings stand
4.7 miles - 2 psi - 70 mph - moderate commercial damage, severe residential damage
7.4 miles - 1 psi - 35 mph - mild commercial damage, moderate residential damage

The blast effect deteriorates quickly over time. At least ten feet of earth above underground bomb shelters will absorb and deflect much of the blast load. Concrete reinforced with compression steel is a good building material for bomb shelters because it has ductile properties - that is, it is more likely to bend rather than break under a blast load. At a minimum, bomb shelters should support a load of 40 pounds per square foot (this from the building code for public fallout shelters).

Thirty-five percent of the energy in a nuclear explosion appears as thermal radiation - visible, infrared, and UV light. This radiation heats a sphere of air around the detonation point into a luminous fireball typically measuring 20 - 100 million degrees Fahrenheit. The fireball is a thousand times brighter than the sun and can easily blind anyone looking at it. The intensity of the heat is such that, for a one-megaton detonation, any exposed person within five miles of the epicenter would likely die from his burns.

The pulse of thermal radiation lasts for no more than a few seconds. It emanates from the center of the fireball in a straight line until it strikes matter. If the matter absorbs more thermal energy than its burning point, it will combust. Obviously bomb shelters should be built with thick, flame-resistant walls, ceilings, and floors. The outside surfaces should be light-colored or shiny to reflect radiation.

Fifteen percent of the energy in a nuclear explosion goes into nuclear radiation, of which two-thirds is comprised of alpha and beta particles; the remaining one-third is gamma rays and neutrons. Alpha and beta particles can do serious damage if swallowed or inhaled, but they do not travel far in the open air and cannot pass through thin layers of solid material. Gamma rays are a graver threat because they can travel up to a mile in the open air and penetrate deep into solid objects. Once inside a human body gamma rays cause serious damage to tissues and the blood-forming cells.

The nuclear radiation produced by an atomic explosion of more than 50 kilotons has a much shorter range than the blast effect and the thermal radiation, so it is relatively insignificant. However, all material that is vaporized by the fireball (rock, earth, concrete, steel, whatever) is fused with fission products and thrown up into the atmosphere as an enormous mushroom cloud in the case of a ground detonation. This radioactive debris can be scattered over thousands of square miles by the winds, and once it has fallen to the ground it continues to emit radiation. This indirect nuclear radiation, or fallout, is very significant, as it can pose a hazard for days, weeks, months, even years.

Four feet of earth cover is sufficient to block gamma rays. Bomb shelters should contain a fallout meter to determine when the radiation outside has fallen to safe levels.

To be continued.

Back to Part I

Part III - served up by Oven @ 6:04 PM