Nuclear Blast Radius: Damage Zones From Federal Planning Guidance

The area damaged by a nuclear explosion depends on its size, its height and the place it hits. US federal planners use three damage zones. The figures below come from their guidance, and are planning approximations for a ground-level explosion in a city, not predictions.

Damage zones by size of explosion

These distances are from Table 1.2 of the federal planning guidance.

Planners use 10 kilotons as a reference case for a ground-level attack on a city. The table does not cover larger weapons, whose zones would extend farther.

What each zone looks like

• Severe damage. FEMA says few buildings will be structurally sound or standing and very few people are expected to survive. Streets are impassable and there are probably dangerous radiation levels outdoors. Some people inside large structures, such as underground parking garages or subway tunnels, may survive.
• Moderate damage. Substantial building damage, winds briefly above 100 mph, overturned cars, downed utility lines, some collapsed buildings and fires.
• Light damage. Most windows break, many with enough force to cause injuries from flying glass. Beyond this zone, windows facing the blast may still break for many miles. The earlier edition of the guidance says some may break more than 10 miles away.

The blast is not the only danger

Fallout can be dangerous far beyond the damage zones, with lethal levels possible tens of miles from ground zero in the first few hours. Outside the damage zones, what you do next matters most.

What to do

Ready.gov gives these steps:

1. If you have warning, take cover from the blast behind anything that might offer protection. If you are outside, lie face down to protect exposed skin from the heat and flying debris.
2. After the shockwave passes, go inside the nearest building as quickly as possible.
3. You will have 10 minutes or more before fallout arrives. If a multi-story building or basement can be safely reached within a few minutes, go there immediately.
4. Stay in the basement or the center of a large building for the first 24 hours, unless there is an immediate hazard or authorities say it is safe to leave.

Being outdoors in the first minute after a detonation may result in death, severe burns and other injuries from blast and heat, and the risk rises the closer you are. FEMA says seeking shelter before a detonation, in an attack warning, can significantly reduce blast, heat and radiation effects.

See what counts as adequate shelter and what fallout maps can tell you.