This is the best place to hide from a nuclear explosion

[July 13, 2023: Ashley Piccone, American Institute of Physics]

There is no good place to be when a nuclear bomb goes off. Anything too close is instantly vaporized, and radiation can pose a serious health threat even at a distance. In between, there is another danger: the blast wave generated by the explosion, which can produce airspeeds strong enough to lift people into the air and cause serious injury.

The shock waves and thermal and ionizing radiation will cause destruction. Moreover, radioactive fallout will impact for years. The shock waves will cause most of the damage through fast changes in air pressure that will destroy people, trees, and manufactured structures. The destruction will depend on the magnitude of the explosion, and the greater the distance one wants to achieve, the greater the burst height should be. Air bursts will result in higher overpressures at longer distances. In contrast, surface explosions will lead to higher overpressures at closer distances.

Although estimating the various effects at different distances is complicated, a general assessment based on past nuclear tests and engineering projections suggests that overpressures at and above 20 pounds per square inch (psi) will partially or entirely demolish heavy concrete buildings.

At 10 psi, most people will die, and severe damage will occur. At 5 psi, severe injuries and fatalities to humans will be widespread and significant damage to heavy structures will occur. Finally, at longer distances featuring 3 psi, overpressure will result in severe human injuries, and the destruction of smaller built-in structures. For the range of overpressures below 5 psi, humans outdoors will be exposed to the absolute risk of severe injury or death. The blast waves, debris from structures, radiation, and nuclear fallout will cause the above.

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Several studies in the past have simulated the dispersion and deposition of radioactive fallout from nuclear tests or terrorist nuclear detonations and modeled the radioactive fallout from stabilized nuclear clouds and atomic weapon tests. Obviously, near the nuclear bomb detonation, the devastation would be widespread, and the fatality rate would be practically 100%. However, outside of the severe damage zone (SDZ), the effect of the blast reduces and survivability increases.

Severe injuries can be reduced at distances corresponding to overpressures below 5 psi, particularly for people inside concrete buildings within the moderate damage zone (MDZ). In this case, the primary danger to human survivability in indoor spaces becomes the extreme high-speed winds that enter through the various openings in the building, e.g., windows. In addition, the propagation of shock waves indoors will interact with walls and deflect around corners, doors, and obstacles. These interactions may induce higher pressures due to channeling effects, thus increasing the injury risk.

The problem is multiparametric, as indoor spaces vary depending on obstacles and architectural layout. Thus, the details of the phenomena will be dependent on indoor arrangement. Despite that, significant conclusions can be drawn from the induced forces, which can help minimize the effect of blast impact. This study shows that in the range of nuclear explosion far-field overpressures below 5 psi, the injury for people indoors can vary and be reduced depending on the position of humans in the building.

Tactical nuclear weapons range between 5 and 15 kilotons (kT). In the present study, however, we have chosen a 750 kT atomic warhead as this corresponds to an extreme scenario of an upper range value of a multiple independently targetable reentry vehicle (MIRV), for example, the RS-28 Sarmat (Satan II).

Of course, this scenario is unthinkable, but it represents a catastrophic scenario due to the existence of such a warhead and the increasing geopolitical tensions. Therefore, we aim to alert the world through rigorous scientific simulations of the impact of such a scenario, particularly in MDZ. To the best of our knowledge, no previous studies have examined the risk to humans caused by high-speed winds from nuclear blasts entering buildings within the MDZ.

In Physics of Fluids, by AIP Publishing, researchers from the University of Nicosia simulated an atomic bomb explosion from a typical intercontinental ballistic missile and the resulting blast wave to see how it would affect people sheltering indoors.

In the moderate damage zone, the blast wave is enough to topple some buildings and injure people caught outdoors. However, sturdier buildings, such as concrete structures, can remain standing.

The team used advanced computer modeling to study how a nuclear blast wave speeds through a standing structure. Their simulated structure featured rooms, windows, doorways, and corridors and allowed them to calculate the speed of the air following the blast wave and determine the best and worst places to be.

"Before our study, the danger to people inside a concrete-reinforced building that withstands the blast wave was unclear," said author Dimitris Drikakis. "Our study shows that high airspeeds remain a considerable hazard and can still result in severe injuries or even fatalities."

According to their results, simply being in a sturdy building is not enough to avoid risk. The tight spaces can increase airspeed, and the involvement of the blast wave causes air to reflect off walls and bend around corners. In the worst cases, this can produce a force equivalent to 18 times a human's body weight.

"The most dangerous critical indoor locations to avoid are the windows, the corridors, and the doors," said author Ioannis Kokkinakis. "People should stay away from these locations and immediately take shelter. Even in the front room facing the explosion, one can be safe from the high airspeeds if positioned at the corners of the wall facing the blast."

The authors stress that the time between the explosion and the arrival of the blast wave is only a few seconds, so quickly getting to a safe place is critical.

"Additionally, there will be increased radiation levels, unsafe buildings, damaged power and gas lines, and fires," said Drikakis. "People should be concerned about all the above and seek immediate emergency assistance."

While the authors hope that their advice will never need to be followed, they believe that understanding the effects of a nuclear explosion can help prevent injuries and guide rescue efforts.

The article "Nuclear explosion impact on humans indoors" is authored by Ioannis William Kokkinakis and Dimitris Drikakis.

Note: Materials provided above by American Institute of Physics. Content may be edited for style and length.

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