The reach of a nuclear blast in a densely populated area like New York City depends on the weapon’s size and detonation altitude. Destructive effects radiate outward in zones defined by three forces: the crushing blast wave, the scorching thermal flash, and penetrating radiation. To assess the potential reach, the destructive radii are calculated based on a specific, modern scenario.
Defining the Nuclear Device and Detonation
The power of a nuclear weapon is measured by its “yield,” expressed in kilotons (kT) or megatons (MT) of TNT equivalent. For this hypothetical scenario, the effects are based on a 150-kiloton thermonuclear airburst detonated high above Midtown Manhattan. This yield is representative of modern, high-end warheads and is approximately ten times more powerful than the bomb dropped on Hiroshima.
The method of detonation is equally important. An airburst means the fireball does not touch the ground, maximizing the blast and thermal damage radii over the widest possible area. This maximizes immediate destruction but significantly reduces local, short-term radioactive fallout compared to a ground burst, where soil and debris are irradiated and lofted into the atmosphere.
Mapping the Blast and Thermal Damage Zones
The immediate physical destruction is determined by the blast wave and thermal radiation. The blast wave is measured by overpressure, or the pressure exceeding normal atmospheric levels, which diminishes rapidly with distance from the explosion. The most severe destruction occurs at 20 pounds per square inch (psi) of overpressure, where heavily built, reinforced concrete buildings are severely damaged or demolished.
The most widespread destruction zone, where most residential structures collapse, occurs at 5 psi. For a 150-kiloton airburst, this destructive ring reaches approximately 4.64 miles (7.5 kilometers) from the detonation point. This radius extends damage from Midtown well into the outer boroughs, across the Hudson River into parts of New Jersey, and deep into Brooklyn and Queens. Even a modest overpressure of 1 psi, which can shatter window glass, extends the damage radius to over 10 miles.
Thermal Effects
Thermal radiation, an intense burst of light and heat, often covers a wider area than the damaging blast wave. This energy causes flash burns on exposed skin and ignites flammable materials, accounting for about 35% of the weapon’s total energy release. For the 150-kiloton scenario, the thermal flash capable of causing third-degree burns on exposed skin extends out to about 6.54 miles (10.5 kilometers).
Within this thermal radius, anyone directly exposed to the fireball would sustain catastrophic burns. The heat at this distance is sufficient to start numerous secondary fires, which can coalesce into a massive firestorm, further compounding the physical destruction.
The Extent of Immediate Radiation Danger
Separate from the blast and thermal effects is the threat of prompt, or immediate, ionizing radiation, which is emitted within the first minute of the explosion. This invisible danger consists primarily of gamma rays and neutrons, which penetrate structures and cause acute radiation sickness. The lethal effect is measured in radiation dose, often in Grays (Gy) or Sieverts (Sv).
A dose of 5 to 6 Gy is considered a lethal dose for half of the exposed population, resulting in death within weeks without medical intervention. For the assumed 150-kiloton airburst, the radius where this immediate radiation dose is lethal to 50% of the population is contained within a much smaller circle, extending about 1.24 miles (2 kilometers) from the blast center.
This immediate radiation danger zone is largely contained within the area of total physical destruction caused by the blast and fire. For modern, high-yield airbursts, the blast and thermal effects are so extensive that they encompass the area where the immediate radiation dose is life-threatening. Therefore, most people within the lethal prompt radiation zone would have already perished from the overwhelming physical forces of the explosion.
Understanding the Reach of Radioactive Fallout
The geographical reach of radioactive fallout extends far beyond the immediate zones of destruction, as it is determined by wind and atmospheric conditions rather than the weapon’s yield alone. Fallout is composed of pulverized, radioactive weapon debris and, in the case of a ground burst, irradiated soil that is lofted into the atmosphere. The 150-kiloton airburst scenario produces a relatively small amount of local fallout, as the fireball does not interact directly with the ground.
However, the radioactive plume will still travel downwind in an elliptical pattern, creating a contamination zone that can stretch for tens or even hundreds of miles. If prevailing winds are moving westward, the fallout plume could contaminate areas of Long Island, Connecticut, or New Jersey, creating dangerous “hot spots” far removed from the initial blast site.
The danger from fallout is delayed, with the particles settling over hours or days, and it represents a widespread environmental contamination threat to survivors. The speed and direction of the wind, the time of day, and precipitation all determine the exact path and concentration of the radioactive material. While the physical destruction is contained to the metropolitan area, the environmental reach of radioactive fallout can affect regions hundreds of miles away.