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... and potential deaths from superfires.

U.S. government estimates of urban-fire casualties that might be triggered by the detonation of a 1 megaton (MT) nuclear bomb have been based on the assumption that the casualty rate for any given peak shock wave pressure, or "overpressure," would be similar to that experienced in Nagasaki and Hiroshima. But research by Theodore Postol, a senior analyst at Stanford university's Center for International Security and Arms Control, calls that assumption into question. His calculations indicate that the 15 million deaths this scaling rule suggests might result from 100 1-MT bombs dropped on cities would underestimate -- by a factor of two to foure -- the likely fire deaths.

The thermal energy delivered to regions experiencing similar peak overpressures varies with bomb yield. for example, the 5 pounds per square inch (psi) overpressure zone for a 1-MT bomb would likely experience at least 3.5 times more heat than the 5-psi overpressure zone associated with the 0.15-MT Hiroshima bomb. The zone in which blast-initiated fires develop also scales up with bomb yield. For example, Postol's data indicate that the fire-zone radius associated with a 1-MT blast could be eight miles, and that the 5-psi overpressure zone might be as far as three miles inside this fire zone's perimeter. If true, that might give blast survivors only 10 to 30 minutes (or less) to escape before small fires coalesced into a giant "suprfire" -- with gale force winds circulating poisonous combustion gases and with ground-level temperatures above the boiling point of water. This prospect does not support the earlier speculation that even 30 percent might escape the 5-psi zone relatively unharmed or that only about 30 percent would die outright.

Finally, Postol's data indicate that cities don't have to be as dense -- and hence, fuel-rich -- as Dresden during the 1940s to support a superfire. The higher winds that would accompany the 1-MT bomb's larger fire zones might be able to whip up even a lightly built-up, burning city into a firestorm, he says.
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Title Annotation:likely fire deaths from nuclear bomb
Publication:Science News
Date:Oct 12, 1985
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