This past Friday night, in conversation with a couple of our friends, the subject of high school fears of annihilation came up. Ferrett said he’d done a class project showing how, if New York City got hit with a nuclear warhead, his home town of Norwalk, CT would be destroyed as well.
“Wait a minute, that can’t be right,” I said. “How far is it from Manhattan to Norwalk?”
Still, I felt confident in asserting that no way would Norwalk be destroyed. Not even with a 20-megaton warhead, which was what he remembered using in his example. A few windows might get shattered, and of course if the wind were from the southwest they’d be getting a whole lot of fallout. But flattened? No. I was pretty sure not.
“Hold on,” I said, “I’ll be right back.”
I ran up to the library and went straight to the “military and arms control” shelf, where I pulled out my copy of “The Effects of Nuclear Weapons”, 3rd Edition (1977). In the back, it has this handy “Nuclear Bomb Effects Computer”, a circular slide-rule type of affair. You can fiddle with an online version of the calculator from the 2nd Edition (1962) of the same book, and the complete text of the 3rd Edition is also available online. I went back downstairs and pulled out the calculator.
Humming to myself, I slipped and swished the dials until I came up with the answer a bit more severe than expected, but not terribly far off. At a range of 45 miles, the maximum overpressure for an optimum-altitude air burst with a 20MT yield would be somewhere around 0.8psi. The calculator actually doesn’t show overpressure figures below 1psi for optimum-altitude bursts, though it goes down to 0.1psi for ground bursts. It also doesn’t go any higher than a 20MT yield. A 0.8psi overpressure would shatter most windows, particularly those facing the shock wave, and might cause light damage to some residential homes. The direct thermal radiation, even assuming line-of-sight to the fireball, would be less than 1 cal/cm2, which isn’t enough to cause any damage. Otherwise, there would be a brief pulse of 30-mile-per-hour wind as the shock wave passed, and of course there would be EMP effects. And, you know, fallout.
So it’s not like things would be all peaches and cream for the folks in Norwalk, but the town would still be standing.
At this point, I wondered if there were perhaps a tool online that would show this sort of information more visually. I Googled a bit more, and came up with the Nuclear Weapon Effects Calculator, which lets you pick from a short list of cities, dial up the yield of your explosion, and click on the image to change the detonation point. Guess where they got their data for the thermal ring, as well as the 5psi and 2psi thresholds? Yep: “The Effects of Nuclear Weapons”, 3rd Edition.
That’s when my inner geek kicked into overdrive. I’d been meaning to dig into the Google Maps API anyway, so I signed up for a key and developed my own version. I call it HYDESim, which stands for “High-Yield Detonation Effects Simulator”. You can pick from a list of cities or input any latitude/longitude coordinates Google Maps covers, set the yield you find most interesting, and see what the effects might be. Each successive ring marks a successive overpressure threshold: 15psi, 5psi, 2psi, 1psi. I included 0.25psi in the list because it’s the point at which even windows wouldn’t be damaged, but left it off the map because it was too huge. (I thought about adding a way to switch psi rings on and off, and in the end didn’t feel like doing the necessary hackery.) 15psi is the point at which reinforced-concrete structures might be able to survive with severe damage; 5psi is where homes might start to survive with severe damage; and 2psi is where home damage drops to light. Roughly speaking.
I didn’t include rings for thermal effects or electromagnetic pulses: this is strictly about blast wave damage. It’s also “idealized”, which means that there’s no effort made to account for terrain changes, urban density, ground type, and so on. The script just uses the formulae and information in the book to calculate maximum-overpressure distances for arbitrary yields, and plops down circles as appropriate. So the “Simulator” part of the name is probably exceedingly grandiose. Then again, you never know what a future spate of hacking might bring.
Also: apologies to New Yorkers that your city is the default target, but its destruction and the follow-on physical effects in Norwalk are what got me started on this… and, let’s face it, in any wide-scale nuclear conflict, you’d have been the top city on the target list.
Doing this was an interesting exercise in both Google Maps programming and lightweight AJAX, which I’d also been meaning to investigate; the city list is built from an XML file that sits outside the XHTML document and its scripts. I’ll have some observations about the Google Maps API in another post— specifically, what I found to be major limitations given what I was trying to do— but for now, here’s your chance to get a slightly more concrete idea of what had us all so scared during the Cold War. As the simulator demonstrates, even a 1MT (1000KT) device could do a whole lot of damage.