Chapter 15 · Nuclear and radiological emergency
15.2 What happens in a nuclear detonation
A detonation produces several effects in sequence. Knowing the order tells you what to do at each moment.
| Effect | When | What it does | How you protect yourself |
|---|---|---|---|
| Flash | Instant | Extremely bright light. Temporary blindness: in daytime it can affect people more than 10 miles (16 km) away and lasts seconds; at night it can last 5 to 10 minutes. It can burn the retina several miles away (twice as far at night). | Do not look toward the light. Close your eyes and cover up. |
| Heat (thermal pulse) | Instant, lasts seconds | Burns on exposed skin; fires. | Any shadow or solid barrier helps. Face down, skin covered. |
| Initial radiation | First minute | High dose very close to ground zero; according to FEMA, casualties from initial radiation are minimal beyond 1 mile (1.6 km) in a 10-kiloton detonation. | Mass and distance. |
| Blast wave | Seconds after the flash; several miles out it travels about 1 mile every 5 seconds | Violent winds, collapses, broken glass turned into projectiles miles away. | Get on the ground, behind something solid, away from windows. Wait for it to pass. |
| Electromagnetic pulse (EMP) | Instant | Damages electronic devices several miles away; blackouts that can last hours to days and extend tens of miles beyond the damaged area. | Have a battery-powered or hand-crank radio. Expect cell phone, internet, and power failures. |
| Radioactive fallout (fallout) | Starts falling within minutes; in distant areas, an hour or more | Radioactive particles that fall from the sky in the direction of the wind. It is the greatest danger for most survivors. | Solid building, center or basement, at least 24 hours. |
Damage zones
FEMA describes damage zones for a reference 10-kiloton ground-level detonation in a city. A larger weapon produces larger zones; use them only to understand the logic, not as an exact map.
| Zone (FEMA) | Approximate distance (10 kt) | What to expect |
|---|---|---|
| Fireball | About ¼ mile (400 m) in diameter | Total destruction. |
| Severe damage zone | Up to 0.5 miles (0.8 km) | Few buildings remain standing. Underground areas can protect from radiation. |
| Moderate damage zone | 0.5 to 1 mile (0.8–1.6 km) | Winds over 100 mph (160 km/h), fires likely, many wood-frame houses destroyed. Evacuation priority when it is safe. |
| Light damage zone | 1 to 3 miles (1.6–4.8 km) | Most windows break; glass injuries. There are 10 minutes or more to take shelter before the fallout arrives. |
| Dangerous radiation zone | Can extend tens of miles downwind | Levels of 10 R/h or more outdoors. Peaks in the first hours and then shrinks quickly: it can go from tens of miles to one or two in a day. |
| Hot zone | Can extend hundreds of miles | Measurable contamination (0.01 to 10 R/h). Begins to shrink within the first 24 hours. |
The practical bottom line: most people affected by a detonation would be outside the destruction zones, in the fallout area. For them, sheltering well makes the difference between a dangerous dose and a minimal one. FEMA says the initial "get inside, stay inside" message should be given to everyone within 50 miles (80 km) until the danger zones are identified.
