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The energy of a nuclear explosion is released in the form of a blast wave, thermal radiation (heat) and nuclear radiation. The distribution of energy in these three forms depends on the yield of the weapon. For nuclear weapons in the kiloton range, the energy is divided in various forms, roughly as 50% blast, 35% thermal and 15% nuclear radiation. Each one of these forms causes devastation on a scale that is unimaginable. Below these effects are discussed separately for a 15 kiloton bomb, which was the explosive power of the bomb detonated by the U.S. in Hiroshima during World War II. This is also the size of the weapons now possessed by India, Pakistan, North Korea and would likely be roughly the size weapon created by terrorists.
Because of the tremendous amount of energy released in a nuclear detonation, temperatures of tens of millions of degrees C develop in the immediate area of a nuclear detonation (contrast this with the few thousand degrees of a conventional explosion). This compares with the temperature inside the core of the Sun. At these temperatures, every thing near ground-zero vaporizes (from a few hundred meters in 15 kiloton weapons to more than a kilometer in multimegaton weapons). The remaining gases of the weapon, surrounding air and other material form a fireball.
The fireball begins to grow rapidly and rise like a balloon. As the fireball rises and subsequently expands as it cools, it gives the appearance of the familiar mushroom cloud. The vaporized debris, contaminated by radioactivity, falls over a vast area after the explosion subsides – creating a radioactive deadly fallout with long-term effects.
Figure 1 : Illustration of blast effects for a15 kiloton explosion. Zones 1 and 2 correspond to the "killing field" where the fatalities are universal.
Because of the very high temperatures and pressures at ground zero, the gaseous residues of the explosion move outward. The effect of these high pressures is to create a blast wave traveling several times faster than sound. A 15 kiloton weapon creates pressure created in excess of 10 Psi (pounds per square inch) with wind speeds in excess of 800 km per hour up to about a 1.2 km radius. Most buildings are demolished and there will be almost no survivors (much larger strategic nuclear weapons will greatly extend this radius of destruction).
Beyond this distance, and up to about 2.5 km the pressure gradually drops to 3 Psi and the wind speed comes down to about 150 km per hour as in a severe cyclonic storm. There will be injuries on a large scale and some fatalities. Beyond this zone of fatalities, the pressure drops to less than 1 Psi, enough to shatter windows and cause serious injuries. It is the high speed combined with high pressures which causes the most mechanical damage in a nuclear explosion. Human beings are quite resistant to pressure, but cannot withstand being thrown against hard objects nor to buildings falling upon them.
Blast effects are most carefully considered by military warplanners bent upon destroying specific targets. However, it is the thermal effects which hold the greatest potential for environmental damage and human destruction. This is because nuclear firestorms in urban areas can create millions of tons of smoke which will rise into the stratosphere and create massive global cooling by blocking sunlight. In any nuclear conflict, it is likely that this environmental catastrophe will cause more fatalities than would the initial immediate local effects of the nuclear detonation.
Figure 2 : Illustration of thermal effects for a 15 kiloton bomb. Regions 1, 2, 3 refer to the degree of burns sustained during the explosion. People who sustain third degree burns are unlikely to survive without immediate medical attention
The surface of the fireball also emits large amounts of infrared, visible and ultraviolet rays in the first few seconds. This thermal radiation travels outward at the speed of light. As a result this is by far the most widespread of all the effects in a nuclear explosion and occurs even at distances where blast effects are minimal.
The range of thermal effects increases markedly with weapon yield (thermal radiation decays only as the inverse square of the distance from the detonation). Large nuclear weapons (in the megaton class and above) can start fires and do other thermal damage at distances far beyond the distance at which they can cause blast damage.
Even with a 15 kiloton detonation, the intensity of the thermal radiation can exceed 1000 Watts per square cm. This is similar to getting burnt by an acetylene torch used for welding metals. For a 15 kiloton bomb, almost everyone within 2 km will suffer third degree burns (which damage the skin and tissues below it); for 550 kiloton bomb, third degree burns occur in a radius up to 9 km. There will be almost no survivors since no immediate medical attention will be available (the entire U.S. has specialized facilities to treat 1500 burn victims).
When studying the effects of a single weapon, it is important to remember that thousands of U.S. and Russian nuclear weapons with yields 8 to 50 times larger than 15 kilotons remain on high-alert, quick-launch status. In a U.S.-Russian nuclear war, these scenarios would occur thousands of times over in virtually every major city in the U.S., Russia, and NATO member states (and probably in China).
It is the cumulative effects of these firestorms – the creation of a stratospheric smoke layer resulting in deadly global climate change – which ultimately become the primary environmental consequence of nuclear war which threatens the continued human existence.
There basically are two kinds of ionizing radiation created by nuclear explosions, electromagnetic and particulate. Radiation emitted at the time of detonation is known as prompt or initial radiation, and it occurs within the first minute of detonation. Anyone close enough to the detonation to be killed by prompt radiation is likely to be killed by blast and thermal effects, so most concerns about the health effects of radiation focus upon the residual or delayed radiation, which is caused by the decay of radioactive isotopes and is commonly known as radioactive fallout.
If the fireball of the nuclear detonation touches the surface of the Earth, large amounts of soil, water, etc. will be vaporized and drawn up into the radioactive cloud. This material then also becomes highly radioactive; the smaller particles will rise into the stratosphere and be distributed globally while the larger particles will settle to Earth within about 24 hours as local fallout. Lethal levels of fallout can extend many hundreds of kilometers and miles from the blast area. Contaminated areas can remain uninhabitable for tens or hundreds of years.
Radiation injury has a long-term effect on survivors. Reactive chemicals released by ionization cause damage to DNA and disrupt cells by producing immediate effects on metabolic and replication processes. While cells can repair a great deal of the genetic damage, that takes time, and repeated injuries make it that much more difficult. Immediate treatment requires continual replacement of blood so that the damaged blood cells are replaced, and treatment of bone marrow and lymphatic tissues which are amongst the most sensitive to radiation. One must remember in this context that there are very few hospitals equipped to carry out such remedial procedures.
Radiation injury is measured in a unit called rem. Some authorities consider 5 rem/year tolerable for workers who are occupationally exposed to radiation —a typical value for exposure to medical X-rays is 0.08 rem. 1.5 rem/year is considered tolerable for pregnant women. It should be remembered that natural radiation is always present in the atmosphere over most places on the earth, but at lower levels. However, there is no threshold, universally agreed upon, at which a dose of radiation can be declared safe.
Things which get irradiated by “prompt” radiation themselves become radioactive. People in the area of a nuclear explosion, and those subject to radioactive fallout stand more risk of contracting cancer. A 1000 rem exposure for the whole body over a lifetime (which is entirely possible for those surviving a nuclear war) brings about an 80% chance of contracting cancer.
Cancer from radiation exposure will occur over the entire lifetime of exposed populations. For example, only one-half of the predicted numbers of cancer have occurred in the people exposed to the radiation produced by the atmospheric weapons tests and the explosions of the US atomic bombs in Hiroshima and Nagasaki that took place 50 to 60 years ago.
We have no idea what the long-term genetic consequences will be from the massive release of radioactive fallout on a world-wide basis.
Ionizing radiation from the fireball produces intense currents and electromagnetic fields, usually referred to as the electromagnetic pulse (EMP). This pulse is felt over very large distances. A single high-yield nuclear detonation will create destructive EMP over hundreds of thousands of square kilometers beneath where the explosion occurs.
EMP from high-yield nuclear detonations will subject electrical grids to voltage surges far exceeding those caused by lightning. Modern VLSI chips and microprocessors, present in most communication equipment. TVs, radios, computers and other electronic equipment are extremely sensitive to these surges and immediately get burnt out. Thus all possible communication links to the outside world are cut off. Restoring these facilities will be an arduous (and expensive) task assuming that the infrastructure required to complete this task would still exist following a nuclear war.
Warplanners consider the EMP from the detonation of a high-yield warhead as capable of disrupting the entire communication system of their nation, and in this way a single missile launch could begin a nuclear war.
Massive absorption of warming sunlight by a global smoke layer would cause Ice Age temperatures on Earth. NASA computer models predict 40% of the smoke would stay in the stratosphere for 10 years. There the smoke would also destroy much of the protective ozone layer and allow dangerous amounts of UV light to reach the Earth's surface.
Half of 1% of the explosive power of the deployed nuclear arsenal can create nuclear darkness. 100 Hiroshima-size weapons exploded in the large cities of India and Pakistan would put 5 million tons of smoke in the stratosphere and drop average global temperatures to Little Ice Age levels. Shortened growing seasons could cause up to 1 billion people to starve to death.
A large nuclear war could put 150 million tons of smoke in the stratosphere and make global temperatures colder than they were 18,000 years ago during the coldest part of the last Ice Age. Killing frosts would occur every day for 1-3 years in the large agricultural regions of the Northern Hemisphere. Average global precipitation would be reduced by 45%. Earth’s ozone layer would be decimated. Growing seasons would be eliminated.
A large nuclear war would utterly devastate the environment and cause most people to starve to death. Already stressed ecosystems would collapse. Deadly climate change, radioactive fallout and toxic pollution would cause a mass extinction event, eliminating humans and most complex forms of life on Earth.
The U.S. and Russia keep hundreds of missiles armed with thousands of nuclear warheads on high-alert, 24 hours a day.
They can be launched with only a few minutes warning and reach their targets in less than 30 minutes. We must end this madness.