Are They Useless? VI (of XIV). Heat
So far, we have been addressing only the uselessness that comes from the immense size of the “bang” (as J. Robert Oppenheimer put it) that nuclear weapons make.
When the yield of a nuclear weapon is given, the size of the bang is usually the only effect specified. That size is usually expressed in terms of how much TNT would make a bang that was as big. Expressed not in pounds, as with our conventional bombs, but, given the size of the yields of nuclear weapons, in tons of TNT.
The yields of nuclear weapons are not just bigger than those of conventional weapons however. They are different in crucial respects.
Conventional (also known as “chemical”) bombs do release heat, heat that can start fires. Nuclear weapons also release heat (called “thermal radiation” by the experts), but it is a heat that is so much greater than the heat released by chemical bombs that it seems right to consider it something different not just in quantity but in quality.
“Inside an exploding nuclear weapon,” said our great weapons designer Ted Taylor, “are pressures that are over a thousand million—a billion—atmospheres…. And there are temperatures of 100 million degrees Centigrade.” Not many people could claim to know this kind of thing but Ted Taylor could. 1
The pressures of over a billion atmospheres are what cause the very big bang.
A heat of “100 million degrees Centigrade” is greater than the heat at the center of the sun.
What does heat like that do? Here’s what.
For a distance from the center of the detonation that will vary with the yield of the bomb and the altitude of the detonation--within what is called “the fireball”--the heat will not set fires to materials encountered only because it will vaporize them.
Beyond the fireball, the heat will set on fire, not just some things, but anything that will burn, in all directions. The fires started will grow and contribute in a major way to the damage done by the prompt thermal radiation and blast. At Hiroshima, these secondary fires coalesced into firestorms, tornados of fire, that killed more people and probably destroyed more structures than the blast of the bomb had.
The prompt thermal radiation, the heat, will cause third degree burns to exposed flesh a long way from ground zero. Third degree burns are the worst kind. They may not hurt because the burn has gone so deep that the nerves in the skin have been destroyed.
Official witnesses to actual nuclear tests are of course always stationed far enough away from the detonation that they are not harmed, unless maybe they were looking at the detonation and were blinded, or if radioactive fallout unexpectedly happened to blow their way. Even at these distances, witnesses often report the heat as the most startling and alarming aspect of the experience. Most of us have seen photographs of nuclear detonations. Photographs don’t convey heat.
With nuclear detonations, dangerous heat—heat great enough to cause third degree burns on unprotected flesh and to start fires in any flammable materials—usually extends a good distance beyond the circle where severe blast damage will be caused.
Pictures of the aftermath in Hiroshima show devastation extending as far as the eye can see. Most of this devastation was caused not by blast but by the fires that were started by the thermal radiation from the bomb. Fires that became firestorms. As in some of the Japanese cities firebombed by General LeMay. Pictures of the aftermath in those cities look the same.
Here, from Wikipedia, is a well-known photograph of the back of a boy injured in Hiroshima not by the blast or the fires that followed but by the immediate thermal radiation of the bomb. No one thought the boy would survive, but he did.
The higher the “yield” of the weapon, the farther beyond the severe blast damage will damaging heat reach. During the Cold War, the Soviets built a twenty megaton (20,000,000 ton) warhead for their ICBMs. The detonation of that warhead in an airburst would create the kind of heat we’ve been talking about thirty miles out, twice as far as the severe blast damage would extend.
Among actual witnesses of above-ground nuclear detonations, Harold Agnew must have been unique. On December 2, 1942, as a recent college graduate, he had been present under the football stands at the University of Chicago when the first ever nuclear chain reaction—a controlled nuclear chain reaction in this case—was achieved in Enrico Fermi’s Pile-1, which Agnew had helped build. He then went on to work in the Manhattan Project, and three years later witnessed the first test on earth of an atomic bomb, at Trinity. Less than a month after that, in The Great Artiste, the B-29 that flew with the Enola Gay to Hiroshima, Agnew took the movies of the mushroom cloud over the city that are the only pictures we have from the air of the event. Three days later, at our base on Tinian Island, he helped assemble Fat Man, the bomb that would be dropped on Nagasaki. You may have seen the photograph of him at the base on Tinian carrying in one hand the small reinforced metal box that contained the orange-sized plutonium core for the Nagasaki bomb that yielded the equivalent of twenty-two thousand tons of TNT.
By today’s standards, the Hiroshima bomb, Little Boy, and the Nagasaki bomb, Fat Man, were small bombs. In the 1950’s, however, Agnew also witnessed most of the major hydrogen bomb tests conducted at our Pacific Proving Ground, including the biggest one we ever conducted, Castle Bravo, in 1954. Yield fifteen megatons.
As far as I know, he is the only person who witnessed all that.
From July 1970 to 1979, Agnew served as the third director (following J. Robert Oppenheimer and Norris Bradbury) of the Los Alamos National Laboratory in New Mexico. Los Alamos was where our first atomic bombs were designed, and then the place where most of our nuclear weapons were designed over the years.
In a hearing before the Senate Foreign Relations Committee on September 8, 1977, Agnew testified
…I firmly believe that if every five years the world’s major political leaders were required to witness the in-air detonation of a multimegaton warhead, progress on meaningful arms control measures would be speeded up appreciably.
In 1984, according to an article in the Los Angeles Times, Agnew added that every leader should be in his underwear for the experience “so he feels the heat and understands just what he’s screwing around with….”2
Next: Are They Useless? Another Elided Effect.
Interview with Ted Taylor, October 13, 1986, in Robert del Tredici, At Work in the Fields of the Bomb, Harper & Row, 1987, p. 166
These last few paragraphs about Harold Agnew’s experience appeared in a You Might Want to Know posting in April 2021 that asked “Has Any of Our Presidents Ever Witnessed a Nuclear Detonation?”