Wednesday, October 12, 2005

Big Explosions

I originally put this together in July, 2004. All the links are still good as of this posting.


I just finished reading John MacPhee's The Curve of Binding Energy, which is about nuclear weapon designer and Orion inventor Ted Taylor. I got curious about the largest conventional explosions and the smallest nuclear explosions. I present you with the results of my research.


Big explosions are measured in terms of tons, kilotons (kt), and megatons (Mt) of TNT equivalent. For comparison, the largest oil tankers approach a million tons in displacement. Imagine detonating an equivalent mass of TNT. That's a 1Mt explosion.

Some explosions of varying sizes, listed from smallest to largest:
- Oklahoma City bombing: ammonium nitrate fertlizer bomb, equivalent to 2.5-5 tons of TNT
- MOAB, the largest conventional weapon in the US arsenal: 18,000 lbs of high explosive, or 0.009kt. The "Grand Slam" bomb used by the UK in WWII was of approximately equal yield.
- Hiroshima bomb "Little Boy": 13kt (1/77 of a Mt)
- Nagasaki bomb "Fat Man": 20kt
- Castle Bravo, largest US nuke test: 15Mt (750 x Fat Man)
- Mt. Saint Helens inital explosion: 24Mt (7 by blast, the rest as heat)
- Tunguska blast: 40Mt
- Largest Soviet nuke test, and largest human-generated explosion of all time: 57Mt (2850 x Fat Man)
- Krakatoa: 100-200Mt, depending on who you ask
- The collision of the largest fragment of comet Shoemaker-Levy 9 (fragment G, two miles in diameter) with Jupiter is estimated at about 6 million Mt.


"The largest single conventional explosive detonation was for the demolition of the German fortifications at Helgoland on April 18, 1947. A charge of 4061 tonnes (8,952,961 lb) was detonated by Commissioned Gunner E.C. Jellis of the Royal Navy demolition team headed by Lt. F.T. Woosnam aboard HMS Lasso lying 14.5 km. (nine miles) out to sea."

In 1944, an ammo dump in the British Midlands blew. About 4000 tons of ammo went off. I assume that the resulting explosion was probably well short of 4kt because the total weight of munitions included the metal jackets, projectiles and bullets, and some smoke rounds.

In 1947, two liberty ships full of ammonium nitrate fertilizer blew up in Texas City on the Houston ship channel. One ship held 2300 tons of fertilizer, and the other 1000 tons. The 2300-ton lot blew first, but according to reports the subsequent detonation of the 1000-ton lot was more violent.

"The largest conventional explosion test conducted in the US invovled 4.36x10^9 g of explosive and produced a crater 88.4 m in diameter." That's 4360 metric tons of whammy kablammy, or 4807 US (short) tons, or 4430 avoirdupois (long) tons, or 9,592,000 pounds.


If that last source is right, then Guinness is wrong. The folks at Guinness may be aware of the 4.36kt test shot but not be able to authenticate it for military security reasons. In any case, at least two deliberate conventional explosions have been in the 4kt range--a third of Hiroshima, a quarter of Nagasaki--which is a-freakin-mazing.


Here's an eye-opener for you. The smallest nuclear weapon ever deployed by the US was the Davy Crockett unguided rocket, which had a maximum range (for the 120 mm version) of 1.24 _miles_ and a predicted yield of only 10 tons (comparable to Grand Slam or MOAB, in other words). It could be fired from a jeep. Between 1956 and 1963, 2100 were built. Actual tests of the W54 warhead at the Nevada Test Site in 1962 yielded 18 and 22 tons.

This site lists names, dates, locations, and yields of every US nuclear weapon test, and has pictures of many of the test shots. It is worth reading the details on the Pascal A and Pascal B shots from the Plumbob series. Both were safety tests with zero predicted yield. They actually yielded 55 and 300 tons, respectively, much to the surprise of the assembled observers. According to the site, one of the test shots that "fizzled" (Lassen, also from Plumbob series) had a yield of only 0.5 tons. However, the smallest nuclear explosion was the Able shot from Operation Buster, which had a yield of less than one pound. From the site: "The device achieved supercriticality and produced detectable nuclear output, but the energy produced was negligible compared to the high explosive used."


Fizzles aside, it is clearly possible to design nuclear weapons with predictable yields in the 10-20 ton range, and has been since the 1950s. How small can a nuke get? At some point, the energy released by the high explosive required to achieve supercriticality will be greater than the energy released by nuclear fission. I'm not sure where that point is, and I'm sure it's classified.


If we discount the Buster Able and Plumbob Lassen fizzles, the smallest 'real' nuclear explosion is the W54 test that yielded 18 tons. That's .004 times the size of the LCE listed above. So the LCE and SNE overlap by a factor of about 250.


The Halifax explosion, possibly the largest ever when it happened in 1917, but only about 200 tons of whammy kablammy.

Meteor Crater in Arizona, estimated at 20 Mt.

More on MOAB and other large conventional bombs. Incidentally, the 15,000 lb "daisy-cutters" used by the US to create instant helicopter landing sites in Vietnam and Afghanistan used an ammonium nitrate slurry. Fertilizer, in other words.

Low-yield earth-penetrating nuclear weapons.

Indian and Pakistani nukes may have fizzled.


A page with way too much stuff on war in space, and some pretty cool covers from old pulps and comics:


Dr. Vector

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Anonymous Anonymous said...

I think, if you check your sources, you will find that the 1917 Halifax explosion was larger than you credit it by an order of ten. Having checked several sources, I find that the Halifax explosion is generally rated at approximately 2.9 kilotons, not the 200 tons figure you quote. I have been unable to find reference to a human caused explosive disaster on such a scale. The Heligoland and Minor Scale explosions were controlled detonations, the former to demolish a fortress, the latter to test the effects of truly large explosions by the American military. The Halifax explosion was caused by a collision and fire aboard a freighter loaded with explosives for use in the Great War.

10:26 PM  

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