http://www.johnstonsarchive.net/nuclear/nukergv.html which is copyrighted by Robert Johnston, pasted as fair use in my printed, comb-bound John's Technical Interests Growing Up in the Cold War and Space Race at p. 23. Johnston's article is a remarkable piece. It is set in South Texas, so Texans can really relate to the real malls and schools. It talks calmly about violence done to human bodies and leaves the human suffering to other literature.
Reference
Nanoseconds are very short, light travels about a foot in a nanosecond. 1000 nanoseconds = 1000 ns = 1 μs. 1000 μs = 1 ms. 1000 ms = 1 second. Example: 14.7 s means 14.7 seconds
Richard Rhodes The Making of the Atomic Bomb, Dark Sun
How this information can be unclassified: The Smyth Report, 246 pages, was released to the public just days after the Hiroshima and Nagasaki bombings. It contained technical information that was pretty obvious to physicists. It served to guide the people doing classified work, letting them know what they could talk about. Los Alamos Technical Report 1, LA-1, written in 1943, was declassified in 1965 and in classified form informed workers coming into Los Alamos national laboratory of some basics of bomb work. When John & Margaret visited Los Alamos and the Las Vegas Atomic Testing Museum in 2010, we found a lot of books and displays that showed what used to be secret; an entire hydrogen bomb, disassembled, is open to view, though enclosed by ropes.
Using Johnston's work, which is a fiction piece, derive a timeline for the fusion explosion, detonated at 1.3 mile altitude. The weapon is a 1980s Russian MIRV.
Timeline
Zero time high-voltage charges dump onto the detonator wires from energy-storage capacitors, through a krytron or similar tube. 32 to 132 detonators must explode at the same time, so cables conducting current from krytrons to detonators have to be matched in length; most of the cables droop.
3 ns detonators start the high-explosive (HE) shock waves. 3 ns is from the speed of light in the cables, which is about a foot per nanosecond. 3 ns is a short amount of time, though modern microprocessors have several logic pulses during even one nanosecond.
10 μs shock waves reach the first sphere of metal in the small primary (fission) bomb, having exploded through the fast and slow explosives. Since a microsecond is 1000 times slower than a nanosecond, one can see that the chemistry of the explosion is a comparatively slow thing.
13 μs 5" diameter, enriched-uranium sphere starts symmetric compression. At 5" diameter, the uranium does not constitute a critical mass.
19 μs 5" diam becomes 2" diam, super-critical. This is 16x density. Neutrons fire in from a source to start the fission chain reaction.
For readers not knowledgeable about compression, compression of a solid or a liquid is a Herculean thing to bring about. If you hit a nail with a hammer, there is a tiny shrinkage of the length of the nail for 10 microseconds, maybe one part in 100,000. Another example: the vertical steel columns of a 50-story, steel-framed building compress a little due to all the weight on them. If the weight could be relieved, the compression would relax and the building would get only about 1/4" taller. Another example: if the weight on the ocean above a deep trench didn't compress the water, the water would be only about 1/2" higher.
The compression accomplished in an atomic bomb implosion is a large compression of strong metal, uranium or plutonium, making the volume 15% less or even 96% less. It is a transient effect, the volume regains normal size after the implosion, but really it doesn't because compressing something so much is applying a tremendous force through a distance, which is work or Joules as one learns in high-school physics. The Joules is so much that the temperature of the metal is raised way above its vaporization temperature. Yes, the uranium or plutonium vaporizes in about 3 microseconds during the implosion, and yet the implosion is so finely tuned that the vaporized metal keeps a spherical shape as it is squeezed down.
The force to do these amazing compressions is available from "high explosives," HE, which includes cordite and plastic explosive. Regular TNT is powerful but no where near as powerful as HE. Most HE is manufactured as a hot slurry and poured into molds. Imagine working around heated high explosive chemicals! If you want to learn more about this, look up shaped charge, which is what anti-tank explosives are, able to punch through military armor plate.
19.1 μs Aided by deuterium and intensely radioactive tritium, 80 generations of chain reaction take place in .1 μs. 20 million °C. Even so, most of the uranium does not fission, and comes out of the explosion as dangerous contamination. The chain reaction is stimulated by neutrons, which make the nuclei very unstable.
19.103 μs gamma-ray pulse reaches weapon case, though there may be a short delay getting to the secondary. All the atoms of the weapon are (or will shortly be) now ionized, gaseous plasma but are heavy enough that they don't move very far, yet; inertial confinement. Note just 3ns from the previous time-line point. It is so short because gamma rays are electromagnetic energy traveling at the speed of light; gamma rays are not chemistry. (The speed of light can be much slower in dense materials than in a vacuum or air.)
So far, it has been fission. Now, the fusion starts up.
19.2 μs In the secondary, the 10" diam. Lithium Deuteride (LiD) cylinder compresses to 2" diam. This is 25x density. Also, neutrons from the primary fission get into the central uranium rod, fissioning it and compressing the LiD cylinder from the inside, too. There is fusion for 1 μs until the LiD expands and halts fusion for lack of density.
The only other place fusion is happening is the centers of stars, where temperature and density produce continuous fusion, but at a slow rate; stellar fusion of nuclei produces less energy per volume than the chemical metabolism of a human body. There is also transient fusion in research devices like tokamaks.
20 μs Temperature is 300 million °C. The U238 tamper, initially 1" thick, over the LiD cylinder, fissions for .1μs to double the energy. Total yield is 900 kton, 900 thousand tons of TNT, a smallish hydrogen bomb.
Gamma pulse has reached to 400 meters radius as it flashes out at the speed of light. Some gamma is absorbed by air and re-radiates as hard X-rays. Ionized air contributes to the growing fireball but is conductive and bottles up (reflects) radiation like a mirror. The surface of the fireball emits the first visible flash to be seen by people, before radiation, even gamma, is temporarily bottled up.
700 μs fireball is 65 m radius. This is an important point when one thinks about underground nuclear tests used for "nuclear effects" testing; the explosion is enclosed by rock and there are steel gates or doors that are open to the first flash of radiation (which flashes down a tunnel, irradiating test materials), then the gates are shut and latched by explosions to keep ionized material from destroying the tunnel, though there must be a mighty shock wave. A time like 700 μs is enough time for the doors to close and latch. It is likely that the doors contain water or something else to provide some cooling, so they don't melt from the explosion; the rock around the chamber is definitely melting.
80 ms blast wave separates from fireball, travels initially at mach 10. Fireball is .6 mile diam., surface is cooling with expansion through ultraviolet radiation toward visible radiation. Note that we have graduated from nanoseconds to microseconds to milliseconds. Seconds is the next phase.
Thermal radiation, to miles around, starts as ionization of air reduces and the bottling ends. This becomes an abundant effect at 1.07 s.
Blast wave enters the ground and starts a shock wave in the ground, kicking up thousands of tons of dirt and debris, much of which vaporizes. Debris has initially been pushed out by shock wave, but the motion rapidly reverses. Debris is now sucked toward ground zero by hurricane-force wind as the hot, buoyant fireball, practically a vacuum, starts to lift like a giant helium balloon.
1.07 s fireball 1.1 mi. diam. The second visible flash is released.
1.9 s from any water at the surface, up to 8" of it flashes to steam, a steam explosion. The water in the surface of concrete flashes to steam and explodes the surface of concrete. (Spalling)
8 s fireball stops expanding at 1.3 mi. diam. and reaches ground level. 90% of thermal energy has been released.
Debris sucked into rising fireball is irradiated and some of it becomes radioactive, this will add to fallout. Dusty debris becomes condensation centers for the uranium that remains unfissioned and all the other radioactive vapors, another component of fallout. Much fallout will stay up in the air until it is rained out, up to thousands of miles away, and then there will be concentrations of fallout on the ground and in lakes and rivers.
2.5 miles from ground zero, a very few people who are inside buildings will survive the gamma radiation and blast, which arrives at 7.2 s.
Radiation sickness will kill most at this distance, but with treatment some can survive. The trouble is that with hundreds of thousands of victims in an urban setting, and with communications and transportation wiped out, rescue teams have a hard time getting in. If there is general war with nuclear bombs, like a World War III, there are so few rescuers and so many victims that there won't be any help to come in. If Los Angeles is hit, they have a specially hard time since LA is surrounded by mountains and isolated by deserts.
2.9 miles 1% of people survive, most die as buildings are crushed
4.3 miles people who are outside find their skin burning upon a second or two of exposure to the heat radiating from the fireball. Clothing, paint, and plants burn. Blast arrives at 14.7 s due to the speed of sound. Skin burns because subcutaneous fat instantly liquifies, leaks out through charring skin, and catches fire from the bomb's heat.
9 miles black auto tires ignite, clothing ignites when it is exposed for 5 seconds, skin is burned to second or third degree
23 miles at 1 min 43 s, glass windows blow in and lacerate people, fatally for people who have run to windows in curiosity after seeing the flash or feeling building foundations tremor at 23 seconds
40 miles glass windows blow in. Half a million people are dead in a mixed rural/urban setting, many trapped by fires and unable to crawl out. Large urban zones experience conflagration.
400 miles blast is heard after 31 minutes. Most people at this distance will have learned through radio, TV, or Internet that an attack is underway. Whether they hear the blast depends on how much nearby noise there is, as some places will have vehicle congestion as people flee in panic. Fallout takes hours to arrive, if at all depending on wind direction at various levels in the atmosphere.