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Nuclear Bomb Blast Effects - Northwest Shelter Systems
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Nuclear Bomb Blast Effects

Most city planners estimate that the largest nuclear weapon to be used against populations would be one megaton in size. References in this discussion are, therefore, made to these yields. The nuclear weapons effects of interest are electro magnetic pulse (EMP), radiation, blast, and thermal. We are also including information concerning chemical / biological warfare.

EMP Effect

Most experts agree that a full scale nuclear attack would be initiated by a high altitude (approximately 200 miles high) nuclear explosion, and that it would most probably be deployed from a satellite. A nuclear bomb detonated at that altitude will not damage living tissue, will not cause significant radiation fallout and is not a health threat to the population. The purpose of this explosion is to damage critical electrical circuitry in our retaliatory defense weapons and our military communications capabilities. This is accomplished by means of the electro magnetic pulse (EMP) associated with the explosion. One such explosion could affect an area of a thousand miles in diameter.

Terrorist nations can deploy EMP weapons from surface to air missiles detonated from a ship in our costal waters. Iran’s, Shahab-3 ballistic missile, if armed with a nuclear weapon, would have this capability. North Korea, an ally of Iran, boasts that they already have nuclear weapons with ballistic missiles capable of reaching these heights.

Collectors, such as long runs of cable, house wiring, conduit, large antennas, overhead power and telephone lines, railroad tracks, etc., gather this energy in the form of a strong current and voltage surge. All solid state electronics is vulnerable to this energy surge. The equipment does not have to be attached directly to the collector in order to be damaged. It’s possible for a collector to gather in the order of a joule of energy from a one megaton, high altitude explosion. The fact that a small fraction of a joule can cause permanent damage to electronic devices, shows that the EMP threat is a serious one. The damage to equipment could include automobile ignition systems, telephone and radio communications, airline communications, navigational aids, & computers. The power grid throughout the United States would most probably fail. It is estimated that about 95% of our radio stations would immediately loose transmission in an EMP attack.

If a power drop is detected, care should be taken to test telephones, radio stations, and other equipment for loss of function. Many radio stations have alternate power sources, but only about 5% of our radio stations have been hardened against the EMP. If, after checking a battery powered radio, you find that most of the radio stations are not functioning, you should take shelter immediately.

Immediately after the initial EMP explosion, SLBM’s and ICBM’s would probably be launched against targets in the United States. An ICBM from Russia would reach the center of the continental United States in about 25 minutes. A missile from a submarine could reach us in 8 minutes. However, we are not currently seeing Russian nuclear missile submarines in our coastal waters. The 25 minutes which the power failure alarm will give you could mean the difference between life and death.

If you are asleep, a simple power-drop alarm would awaken you when the power fails. This alarm should be constructed by a certified electrician. Our electrician used a motorcycle horn, a 12 volt battery, a relay switch, and a flasher. The negative line from the battery was connected to the 12 V DC horn. When the 110 V AC currant fails, the relay closes the circuit, which activates the horn. He added a switch to the positive line from the battery to the horn so the horn can be turned off after activation.


If the fireball of the weapon touches the ground, the blast is defined as a `ground burst’. In a ground burst, rock, soil, and other material in the area is vaporized and taken into the cloud. This debris is then uniformly fused with fission products and radioactive residues and becomes radioactive itself. It then falls to the ground as `radioactive fallout’. If the fire ball from the explosion does not reach the ground, the blast is said to be an `air burst’. Radiation (except for initial radiation) does not become a factor in an air burst.

Gamma rays from the fallout can easily be attenuated by incorporating a 90 degree turn in the small diameter entrance. Entrances should not exceed 48 inches in diameter and the total length of the vertical and horizontal run should be no less than 25 feet. Approximately 90% of the gamma radiation is directed into the ground from the vertical portion of the entrance. The other 10% is almost entirely attenuated by the horizontal portion of the entrance. We recommend that the horizontal portion of the entrance be about 10 feet long and that it penetrate the shelter body on the side or on the end plate.

The threat of exposure to initial nuclear radiation is confined to a radius of about one and one half miles from ground zero and would prove fatal to any unsheltered individuals. However, in hardened blast and radiation shelters, such as those that are being built by Utah Shelter Systems, people could survive all nuclear weapons effects, including initial radiation, within three quarter mile of ground zero. Shelters which may be within the initial radiation zone, must have at least 8 ft. of dirt cover and the entrances must be configured with the proper shielding and geometry.

Gamma radiation is a great health problem for a two week period. Everyone should stay sheltered in a good fallout shelter for two full weeks. If blast is not a consideration, 4 feet of earth cover is sufficient to shield from gamma radiation. However, the entrances must still each have the 25 feet with both horizontal and vertical runs.

Alpha and Beta radiation can be stopped by a few layers of paper. However , internal to the body, they are a great health hazard. We must be careful to wash the lids of dust before opening canned food, and wash and peel all exposed fruits and vegetables. Water purification, food preparation, and post war survival will be discussed in another section of this web site.

Blast Effect

In the detonation of a one megaton size weapon (which is roughly equivalent to 1 million tons of TNT), the fireball grows to 440 feet in just a fraction of a second. In 10 seconds, the fireball is over a mile wide. At the same time the fireball is forming and growing, a high-pressure wave develops and moves outward in all directions. This wave of air causes a huge increase in air pressure. At one quarter mile from the crater edge, the overpressures are about 200 psi. It is not expected that nuclear weapons with a greater yield than one megaton would be used against the civilian population. We are, therefore, limiting our discussion of blast effects to that yield.

At approximately 4 miles from the epicenter, the winds are 165 mph and the overpressure is approx. 5 psi. Most homes would be destroyed, but it is possible to survive the blast in a basement shelter at that distance. The radiation shielding from the home, however, may have been destroyed in the blast. At 6 and 7 miles from the epicenter, there would be moderate damage to residences and the likelihood of surviving in a basement is greater.

People housed in hardened blast and radiation shelters, such as are built by Utah Shelter Systems, would be expected to survive all NBC weapons effects at ground zero from an air burst (50 psi), and at one quarter mile from the crater edge from a one megaton yield ground burst. At that proximity, an 8 ft. diameter shelter must have at least 8 feet of dirt cover. A 10 foot diameter shelter must have at least 10 feet of dirt cover over head. Each person must have approximately 10 square feet of shelter space for short term survival (up to 2 weeks). Double this space requirement if the shelter is to be used as a permanent residence.

Thermal Effect

Within less than a millionth of a second of the detonation, large amounts of energy in the form of invisible x-rays are absorbed within just a few feet of the atmosphere. This leads to the formation of an extremely hot and luminous mass called the fireball. If we were standing 50 miles away, this fireball would appear to us to be many more times as brilliant as the noon day sun.

You should never look directly at the fireball of a nuclear explosion. Because of the focusing action of the lens of the eye, especially at night when our pupils are open, thermal radiation can cause temporary and even permanent blindness.
The thermal pulse travels at the speed of light and can last for a fraction of a second, up to several seconds. It also generally travels in straight lines, as does light. If there is no warning, you should drop and cover immediately. If you do have warning, you should take cover behind a large structure, or go to a basement or culvert. If unprotected you would receive third degree burns at 6 to 8 miles from the blast; second degree burns at a distance of 8 to 10 miles; and first degree burns at 10 to 12 miles from the blast. Burns would greatly complicate an otherwise survivable situation.

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