Understanding the Mother of All Bombs

This bomb discussion will end with an interesting insight into the politics of Afghanistan. In between, there will be blast tables provided by the BATF.

Foreign policy lives at the intersection of national interests, personalities, and the physical world. In the past few days, there has been a tremendous amount written about the MOAB, making it sound controversial, when it really is no more than a very jumbo fire cracker.

There is no reason to doubt General Nicholson’s statement (Reuters). Quoting:

“This was the first time that we encountered an extensive obstacle to our progress,” he said of a joint Afghan-U.S. operation that has been targeting Islamic State since March.

“It was the right time to use it tactically against the right target on the battlefield.”

Afghan and U.S. forces were at the scene of the strike and reported that the “weapon achieved its intended purpose,”, Nicholson said.

Some of the smaller websites have published outlandish statements on the destructiveness of the MOAB. It has even become political capital, as a symbol of unstoppable power, and a novel evil.  The former president of Afghanistan,  Hamid Karzai tweeted (Al Jazeera),

“This is not the war on terror but the inhuman and most brutal misuse of our country as testing ground for new and dangerous weapons.”…

“I vehemently and in strongest words condemn the dropping of the latest weapon, the largest non-nuclear , on Afghanistan by US…1/2″

Some students of international relations, a quintessential liberal arts major, may have slept through their “physics for poets” course. This is for them. It’s also for the reporter or digger who wants to understand whether a currently circulating attitude is the result of propaganda, political posturing, or a media-frenzy feedback loop. At this point, the words-in-print this past week about the MOAB could be as much as 10% of that devoted to  the sarin gas attack. But the two events are in no way commensurate.

Let us compare. The MK-84 2000 pound bomb has a 1000 pound case. On detonation, the case turns into shrapnel with a 400 yard lethal radius. The blast radius is much smaller than the shrapnel radius.

The MOAB contains 18,700 pounds of high explosive. It has a thin skin of aluminum. On detonation, the skin vaporizes. With possible exception of a few fragments of tail and bits of fin, there is no shrapnel. While high explosives differ in detail, they are more similar than different. The Bureau of Alcohol, Tobacco, Firearms, and Explosives finds no need to distinguish between the varieties of high explosive. The MOAB is not a fuel-air or thermobaric bomb, which would alter the discussion.

Now consult the BATF table, which provides safe storage distances for high explosives based on weight. Consult the column for a highway with more than 3000 cars per day, in straight line of sight of the explosive (unbarricaded.)

  • If the 2000 pound bomb, containing 1000 pounds of explosive, does not have a case that turns into shrapnel, the safe storage distance  is 636 feet.
  • For the MOAB, which contains 18,700 pounds of HE, the safe storage distance is about 1650 feet.

Note that 18,700 pounds of explosive increases the safe distance by only a factor of 2.5. But what is the lethal distance? Clearly, it must be a fraction of the safe distance. A bomb creates a brief pulse of overpressure. (CDC, pdf) Explosions and Refuge Chambers, Table 1 shows no direct damage to the human body by overpressure of 2 pounds/square inch.

At what distance is the overpressure greater than than 2 PSI?  From FEMA (Chapter 4, pdf)  EXPLOSIVE BLAST 4, figure 4.6,

  • 2000 lb bomb with 1000 lb of explosive:  less than 260 feet.
  • MOAB: less than 700 feet.

Somewhere inside the above circles, lethal effects occur. But the 2000 lb bomb has a lethal shrapnel radius of 1200 feet. The MOAB produces little or no shrapnel. We have the surprising conclusion that the MOAB is less likely, in many circumstances, to produce collateral casualties than the ubiquitous MK-84 bomb!

This is not a pleasant subject. Students of IR may prefer to contemplate Metternich or Bismarck. But there is actually an interesting takeaway. Hamid Karzai is still an important political figure in Afghanistan. His polarized comments on the Big Firecracker (I’m giving the MOAB my own name) indicate he is hedging his bets on the future of Afghanistan. As the situation in Afghanistan continues to evolve, he is a man to watch.

But this newly released footage of the MOAB in action could change my mind. What do you think?





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