What distance from a 1 megaton airburst is required to avoid fatal blast overpressure?

1. What “fatal blast overpressure” usually means — and why single numbers mislead

Blast overpressure is the peak pressure above normal atmospheric pressure carried by the shock wave; specific overpressure values are associated with approximate outcomes (e.g., building collapse, life‑threatening injuries). However, survivability depends on more than peak overpressure: wind speed, debris, building type, firestorms, and duration of the pressure impulse matter ^{[4] [1]}. Because different authors use different thresholds (e.g., 5 psi for destructive damage vs. 20 psi for near‑complete structural collapse), quoting a single “safe” distance without stating which effect you mean is misleading ^{[5] [4]}.

2. Direct blast-only ranges reported in technical references

Published blast‑effect studies and compilations give ballpark radii for destructive overpressures. For example, a commonly used “destructive” radius defined by >5 psi is about 4.4 miles (≈7.1 km) for a 1‑megaton airburst in one visualization ^[5]. Glasstone & Dolan describe large overpressures concentrated nearer ground zero and give specific timings and radii for the Mach front and high overpressure regions for a 1‑Mt airburst at particular heights (e.g., a 1.3‑mile radius for a Mach effect region in one scenario) — showing that severe overpressure is concentrated within a few miles ^[4].

3. Fire, thermal radiation and conflagration expand the lethal zone

Analyses that include thermal ignition and ensuing firestorms project substantially larger fatality radii than blast‑only calculations. The NCBI/Medical Implications of Nuclear War report notes conflagration radii for a 1‑Mt airburst could range from about 4 to 14 km depending on atmosphere and building types, and that including fire effects can increase fatalities by factors of two to four relative to blast‑only models ^{[2] [3]}. Britannica similarly states that “Within 8 km (5 miles) few people in the open or in ordinary buildings will likely be able to survive,” emphasizing thermal and debris hazards as well as blast ^[6].

4. Public summaries and visual tools — useful but simplified

Public‑facing graphics and simulators (e.g., Radical Statistics / Statista chart, NUKEMAP, various blast simulators) typically translate peak overpressure contours into colored radii: severe damage within a few miles, moderate damage further out, burns and fires extending tens of miles in some depictions ^{[7] [8] [9]}. These tools are useful for intuition but simplify complex physics like burst altitude, atmospheric conditions and urban geometry, which strongly affect outcomes ^{[8] [10]}.

5. Altitude, terrain and urban form matter — context changes distances

Many authoritative figures (Glasstone & Dolan and follow‑on analyses) compute radii for specific burst heights because optimum air‑bursting maximizes blast range; changing altitude, local atmosphere, and whether the burst is over a dense urban area versus open ground alters the lethal zones significantly ^{[4] [11]}. The NCBI work uses a 2‑km burst scenario to show how predicted fatality radii shift with assumptions ^[2].

6. Practical takeaway for readers seeking a simple guidance

If you mean “avoid almost‑certain immediate fatality from blast and collapse,” contemporary technical sources cluster around a few kilometers (several miles) as the worst‑case lethal blast region for a 1‑Mt airburst; if you include fires and thermal ignition the radius of likely fatalities increases, with credible midrange estimates from roughly 4 km up to 12 km or more under some conditions ^{[1] [2] [3]}. Public tools and popular summaries often state severe damage within ~4 miles (≈6–7 km) and significant effects out to 10+ miles for other hazards ^{[9] [5] [7]}.

Limitations and disagreements: the sources differ because they use different definitions (blast overpressure threshold vs. conflagration or thermal injury), burst heights, and urban assumptions; available sources do not provide a single authoritative “safe” distance that applies to every situation ^{[4] [2] [10]}. Where precise planning or emergency guidance is required, official civil‑defense documents and blast calculators that allow you to set yield, burst altitude, and terrain give the needed specificity ^{[8] [11]}.

If you want, I can: (a) convert the cited radii into maps for a specific city using an online simulator, or (b) extract the overpressure thresholds and corresponding distances from Glasstone & Dolan and present them in a compact reference table (using only the cited sources). Which would you prefer?