No More HIROSHIMA - The Testament of the Atomic Bomb Victims of Hiroshima
The Darkness Immediately after the Explosion -- Why did it get pitch-dark?
Tsutomu IGARASHI
In Chiyoko KUWABARA’s testimony, she mentioned that “it got pitch-dark” right after the explosion. In others’ atomic-bomb testimonies on record, we often find descriptions of “a shroud of darkness”. What’s the cause of it? I would like to infer the cause based on “Genshibakudan Saigai Chousa Houkokushu (Collection of Investigation Reports on Atomic Bomb Disaster)”published by the Japan Society for the Promotion of Science, 1953.
Could only dust cause that darkness? What caused the light to be completely blocked for as long a few dozen minutes? I think this can relate how tremendous the atomic-bombing was. Considering that not only the people indoors but the people outdoors like Chiyoko KUWABARA were also shrouded in darkness, it seems that some more complicated and fierce mechanism was hidden in this phenomenon of darkness.
At the point of atomic-bomb explosion above ground zero, “the temperature rose up to the extreme heat of a few million degrees Celsius and a fireball of several hundred thousand atmospheric pressures was created”, the Report says. It continues that “following that explosion the bomb blast (a shock wave and the blast wind), heat rays (infrared rays and visible rays) and initial radiation (gamma ray and neutron) were emitted.” (all information is by courtesy of Kunio NAGATA, teacher at Hiroshima Municipal Ujina Junior High School)
What happened at first was that, by the creation of a fireball, heat rays were emitted and everything was incinerated in a split second. Even on the ground in the hypocenter vicinity, temperatures reached several thousand degrees Celsius. Melted roof tiles and glass can verify that. Heat rays burned out everything. But it only lasted a moment. It says “The fireball blazed for ten seconds”, but I presume in fact it blazed for a second or two and lost its intense heat rapidly. So we can suppose that everything was ignited at that moment due to the heat of several thousand degrees Celsius.
Every organism exposed directly to the heat rays was burned. Trees, grass, houses, and walls, anything burnable was charred when they were exposed to the heat rays and their surfaces also became rough and were bubbled by the intense heat.
There are two things we tend to overlook: First are particles in the air. Numerous fine particles like dust and specks are suspended in the air. Those particles would be charred in a moment.
Related to this, U. S. bombers like the Enola Gay were strictly prohibited to bomb with radar; bombing by sight was always required. After studying the long term records of weather, they intentionally chose a fine clear day. The U.S. Forces really emphasized bombing by sight.
This was because bombing by sight was more accurate. But a more important reason was, if there were clouds, heat rays and radiation would be blocked by the particles in the clouds, and the effects halved. Absorbing the heat rays and the blast, clouds reduce the effects of bombing. If it is raining on the ground, the effects are much more reduced, not only by the particles in clouds but also by the water drops from them. Observation of the explosion also can be disturbed.
That was why they desperately needed a fine clear day for the world’s first atomic bombing. In other words, they chose a clear day not for bombing by sight but more to maximize the effects. As a result, bombing by sight required fine weather to target accurately, and bombing with radar was banned for that purpose.
I guess the U.S. already knew about the phenomenon of particles in the air burning and had its data. Charred particles were one of the factors causing the darkness we can’t overlook.
What also burned was the skin of animals and people’s clothes, as Kunio NAGATA, teacher at Hiroshima Municipal Ujina junior high school, mentioned.
When hibakusha were badly damaged by the atomic bombing, they were almost naked. Where were their clothes? At the first stage of the explosion the clothes exposed to the heat got charred and tattered instantaneously. And the heat rays penetrated the clothes, more heat absorbed at the dark parts of clothes, and then burned the skin. The skin also got burned and was hanging like rags. Naturally some parts of their hair got burned, too.
At the second stage, the blast came with the velocity of several hundred meters per second, sweeping away those charred organic materials. So what was left were people whose clothes and burnt skin had been swept away. People were naked or had their flesh exposed without skin. At the same time dirt and burned objects rushed back to them, made their faces filthy, terribly distorting their appearances. The blast wind would carry away some parts of the tissue-damaged skin. There were many people with the remnants of their torn skin hanging from their bodies.
We can see the fierceness of the shock wave from the Atomic-bomb Dome which was almost directly under the explosion. With that super high pressure hitting the ground it is not hard to imagine that the shock wave scooped out the soil and produced tremendous dust. Dust, houses, debris, concrete, and broken roof tiles were all swirled up and then blown away outwards.
And the shock wave hit not only once but twice. First the shock wave generated by the explosion traveled outward with a force several hundred thousand times normal atmospheric pressure. Then, because of the extremely low pressure at the center area, it became a vacuum; and then air rushed back in from the area around it with tremendous speed. That means people were stripped naked by the two blast winds in a few seconds.
The air that rushed in contained all sorts of burnt objects you can think of, including soot, dirt, dust, and the wreckage of buildings, blowing back towards the point of detonation 580 meters above the ground. Inorganic matter didn’t change color much but organic matter got charred and rushed back in. Trees, grass, particles in the air, skins of creatures, clothes, charred human skin and hair, all were absorbed and concentrated. Those which heated to a higher temperature went up further from the central point, forming a huge umbrella which was the lower part of the mushroom cloud. The reason that the lower part of the cloud was dark was that it contained incinerated objects. It was not just due to dirt or debris. We should assume that only incinerated objects which have lighter mass could go that high up.
Those objects went up to the sky and immediately formed a kind of a dome. Directly below it objects had already ignited and were flaming up. With this heat some parts kept rising up forming cumulonimbus cloud. The dome with a 1 kilometer- radius containing these incinerated substances was formed in the sky over ground zero, light was blocked and the ground was shrouded in darkness. This was what happened in just dozens of seconds.
The top of mushroom cloud reached about 9000meters high 8 minutes after the explosion.
Just then the wind was blowing from south-east. The rising cumulonimbus cloud drifted to the north-west as time went by, then was exposed to cold air and became rain that fell on the ground. This is “black rain”. The black rain contained charred organisms, namely burned human skins, hair and burned up clothes. This black rain also contained a great deal of radioactive substances.
The dozens of minutes of darkness generated by the atomic bombing symbolizes the tremendous power and its realities of it. It can be said that the fact that people were stripped naked in a split second led to this dome of darkness. We can also say the dome contained very small amount of burnt skin and clothes and blocked light.
Try to imagine the awful destructive power.
Hiroshima Blue Sky Society