This was a relatively low yield air burst. I can't make a reasonable estimate of the yield and some of the visuals seem contradictory. After all, it was a movie.
The shot tower appeared to be much taller, several times the 100 ft height of the tower used for Trinity some eight years earlier. This would suggest that they planned a higher yield. However, the car took only a minute or two to drive at low speed, less than twenty miles per hour from within a hundred yards of the shot tower back to the ghost town. The fireball appears not to have reached the ground, so it must have been in the lower tens of kilotons, at most. The shock wave was strong enough to flatten wooden buildings and roll an automobile multiple times, but the photoflash did not appear to ignite the wooden structures, and it certainly should have at least scorched them. The strength of the shock wave suggests several tens of kilotons, unless you consider that they may well have been within a few hundred yards of the hypo center, less that 1/4 mile or 400 meters from the center of the blast. In that case, then the yield may have been even smaller than Fat Man. That is, less than 20 kT.
The horizontal mine shaft appeared to be at a right angle to the expanding shock wave. If the people were only a few feet within the mine shaft it certainly would have protected them from the flash burns, immediate gamma-ray and high energy beta radiation, and probably any residual neutrons that would have been well spread out by that point. The effect of the supersonic blast wave passing the open end of the mine shaft is harder to predict. There would be a sharp increase in pressure that would send a shock wave into the shaft, but it would be greatly blunted by the sharp edge and the rapid passage. Then the low pressure behind the wave front would tend to "pull" air out of the shaft. But this wouldn't last long before return wave went back the other way. The people in the mine shaft might very well survive with little additional trauma, additional to what they had suffered from the criminals.
"Fallout" would not be an issue for at least hours, if not days. That is, the bomb components and material lifted by hot gasses into the atmosphere would come back down gradually over an extended period of time and most of them would be downwind. There would be an increase in local radioactivity due to neutron activation of the materials in the environment. But this would not be a huge increase. Provided that they were recovered by service personnel within a few hours and taken to a decontamination facility where they could strip, shower and scrub, perhaps multiple times, and then receive non-contaminated clothes, they might come out of this in pretty good shape.
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Flickers-4
8 years ago
Great description of survivability. Pressure inside the cave never occurred to me, but I figured the cave opening was at an angle where the blastwave couldn't enter. This scene stuck with me since I was five years old...driving up to the tower and the car being thrown about and my memory of a real looking car with people in it on fire, of course when I saw it after these many years, it's a model.
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